35 results on '"Andrew J Studer"'
Search Results
2. Austenite formation kinetics from multicomponent cementite-ferrite aggregates
- Author
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Andrew J Studer, Christopher Hutchinson, W.W. Sun, Y.X. Wu, A. Arlazarov, Lingyu Wang, Mark J. Styles, and Y. Bréchet
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010302 applied physics ,Austenite ,Materials science ,Polymers and Plastics ,Cementite ,Diffusion ,Kinetics ,Metals and Alloys ,Thermodynamics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Metastability ,Ferrite (iron) ,0103 physical sciences ,Ceramics and Composites ,0210 nano-technology ,Dissolution - Abstract
Metastable austenite strongly influences the mechanical properties of many advanced high strength steels (AHSS) and its formation kinetics during intercritical annealing strongly depend on the initial microstructure. In this contribution, we have performed detailed kinetic studies of austenite formation from cementite-ferrite aggregate in a range of Fe-C-Mn and Fe-C-Mn-Si/Al alloys via in situ neutron powder diffraction. Depending on the relative contribution of cementite dissolution in respect to migrating interface of austenite/ferrite, the incomplete dissolution of enveloped cementite limited by slow diffusion in austenite could result in austenite plateauing below equilibrium, while fast dissolution of matrix cementite could result in austenite plateau above equilibrium. Both contributions need to be considered and modelled to describe the austenite formation kinetics.
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- 2020
3. Structure-Driven, Ferroelectric Wake-Up Effect for Electrical Fatigue Relief
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Andrew J Studer, Li Jin, Qian Li, Teng Lu, Xiaoyong Wei, Zhuo Xu, Raymond Withers, Yun Liu, Ye Tian, and Dehong Yu
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Materials science ,Condensed matter physics ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,Wake ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,0104 chemical sciences ,Materials Chemistry ,Antiferroelectricity ,Crystallite ,0210 nano-technology ,Polarization (electrochemistry) - Abstract
In this work, we report the first observation of a structure-driven ferroelectric (FE) wake-up effect in polycrystalline AgNbO3-based antiferroelectric (AFE) materials, by which polarization gradua...
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- 2020
4. Symmetry-mode analysis for intuitive observation of structure–property relationships in the lead-free antiferroelectric (1−x)AgNbO3–xLiTaO3
- Author
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Y. Mendez-González, Ye Tian, Teng Lu, Zhuo Xu, Garry J. McIntyre, Xiaoyong Wei, Narendirakumar Narayanan, Li Jin, Raymond Withers, Yun Liu, Andrew J Studer, Dehong Yu, Haixue Yan, Qian Li, and Aimé Peláiz-Barranco
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Phase transition ,Materials science ,symmetry-mode analysis ,Field (physics) ,materials science ,inorganic materials ,02 engineering and technology ,Dielectric ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Condensed Matter::Materials Science ,Antiferroelectricity ,General Materials Science ,Ceramic ,lcsh:Science ,Condensed matter physics ,General Chemistry ,inorganic chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Ferroelectricity ,Research Papers ,Symmetry (physics) ,0104 chemical sciences ,phase transitions ,Hysteresis ,crystal engineering ,visual_art ,visual_art.visual_art_medium ,lcsh:Q ,anti-ferroelectricity ,0210 nano-technology - Abstract
Symmetry-mode analysis has been used to construct the direct linkage between structure and properties for (anti)ferroelectric materials., Functional materials are of critical importance to electronic and smart devices. A deep understanding of the structure–property relationship is essential for designing new materials. In this work, instead of utilizing conventional atomic coordinates, a symmetry-mode approach is successfully used to conduct structure refinement of the neutron powder diffraction data of (1−x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics. This provides rich structural information that not only clarifies the controversial symmetry assigned to pure AgNbO3 but also explains well the detailed structural evolution of (1−x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics, and builds a comprehensive and straightforward relationship between structural distortion and electrical properties. It is concluded that there are four relatively large-amplitude major modes that dominate the distorted Pmc21 structure of pure AgNbO3, namely a Λ3 antiferroelectric mode, a T4+ a − a − c 0 octahedral tilting mode, an H2 a 0 a 0 c +/a 0 a 0 c − octahedral tilting mode and a Γ4− ferroelectric mode. The H2 and Λ3 modes become progressively inactive with increasing x and their destabilization is the driving force behind the composition-driven phase transition between the Pmc21 and R3c phases. This structural variation is consistent with the trend observed in the measured temperature-dependent dielectric properties and polarization–electric field (P-E) hysteresis loops. The mode crystallography applied in this study provides a strategy for optimizing related properties by tuning the amplitudes of the corresponding modes in these novel AgNbO3-based (anti)ferroelectric materials.
- Published
- 2019
5. Negative Thermal Expansion of Ni-Doped MnCoGe at Room-Temperature Magnetic Tuning
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Wayne D. Hutchison, Jianli Wang, Haidong Zhou, Andrew J Studer, Guohua Wang, Jie Ma, Stewart J Campbell, and Qingyong Ren
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Materials science ,Condensed matter physics ,020502 materials ,Doping ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Physical property ,Magnetic field ,0205 materials engineering ,Negative thermal expansion ,Clausius–Clapeyron relation ,Diffusionless transformation ,Lattice (order) ,General Materials Science ,0210 nano-technology ,Magnetic manipulation - Abstract
Compounds that exhibit the unique behavior of negative thermal expansion (NTE)-the physical property of contraction of the lattice parameters on warming-can be applied widely in modern technologies. Consequently, the search for and design of an NTE material with operational and controllable qualities at room temperature are important topics in both physics and materials science. In this work, we demonstrate a new route to achieve magnetic manipulation of a giant NTE in (Mn0.95Ni0.05)CoGe via strong magnetostructural (MS) coupling around room temperature (∼275 to ∼345 K). The MS coupling is realized through the weak bonding between the nonmagnetic CoGe-network and the magnetic Mn-sublattice. Application of a magnetic field changes the NTE in (Mn0.95Ni0.05)CoGe significantly: in particular, a change of Δ L/ L along the a axis of absolute value 15290(60) × 10-6-equivalent to a -31% reduction in NTE-is obtained at 295 K in response to a magnetic field of 8 T.
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- 2019
6. Enhanced antiferroelectric phase stability in La-doped AgNbO3: perspectives from the microstructure to energy storage properties
- Author
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Shujun Zhang, Jing Gao, Qing Liu, Jing-Feng Li, Lei Zhao, Andrew J Studer, Manuel Hinterstein, Kai-Yang Lee, and Yichi Zhang
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Materials science ,Renewable Energy, Sustainability and the Environment ,Neutron diffraction ,Doping ,02 engineering and technology ,General Chemistry ,Dielectric ,021001 nanoscience & nanotechnology ,Microstructure ,Energy storage ,Ion ,Condensed Matter::Materials Science ,Chemical physics ,visual_art ,visual_art.visual_art_medium ,Antiferroelectricity ,General Materials Science ,Ceramic ,0210 nano-technology - Abstract
La-doped AgNbO3 lead-free ceramics were fabricated by conventional solid-state reaction, and the phase stability and energy storage properties were investigated. The temperature- and electric field-dependent dielectric constants show that the antiferroelectric (AFE) phase stability is enhanced via the La doping. Neutron diffraction was performed to obtain insights into the structural evolution with composition and temperature, where the local structural variation is found to involve subtle ion displacement as well as oxygen octahedral tilting, leading to the disruption of the long-range interactions, which is responsible for the enhanced AFE phase stability. As expected, the enhanced AFE phase stability, together with the improved breakdown strength, gives rise to a high energy density of 4.4 J cm−3 and an improved efficiency of 70%, which are achieved in 2 mol% La-doped AgNbO3 ceramics. Our research opens a new way to tailor the macroscopic properties by tuning the microstructure of AgNbO3-based materials.
- Published
- 2019
7. Lead-free (Ag,K)NbO 3 materials for high-performance explosive energy conversion
- Author
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Teng Lu, Fei Xue, Narendirakumar Narayanan, Hengchang Nie, Xianlin Dong, Yun Liu, Long Qing Chen, Dehong Yu, Felipe Kremer, Zhen Liu, Genshui Wang, Andrew J Studer, and Raymond Withers
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Phase transition ,Work (thermodynamics) ,Multidisciplinary ,Materials science ,Explosive material ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,Energy storage ,0104 chemical sciences ,Microsecond ,Lead (geology) ,Chemical physics ,Energy transformation ,0210 nano-technology ,Energy (signal processing) - Abstract
Explosive energy conversion materials with extremely rapid response times have broad and growing applications in energy, medical, defense, and mining areas. Research into the underlying mechanisms and the search for new candidate materials in this field are so limited that environment-unfriendly Pb(Zr,Ti)O3 still dominates after half a century. Here, we report the discovery of a previously undiscovered, lead-free (Ag0.935K0.065)NbO3 material, which possesses a record-high energy storage density of 5.401 J/g, enabling a pulse current ~ 22 A within 1.8 microseconds. It also exhibits excellent temperature stability up to 150°C. Various in situ experimental and theoretical investigations reveal the mechanism underlying this explosive energy conversion can be attributed to a pressure-induced octahedral tilt change from a−a−c+ to a−a−c−/a−a−c+, in accordance with an irreversible pressure-driven ferroelectric-antiferroelectric phase transition. This work provides a high performance alternative to Pb(Zr,Ti)O3 and also guidance for the further development of new materials and devices for explosive energy conversion.
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- 2020
8. Practical high-performance lead-free piezoelectrics: Structural flexibility beyond utilizing multiphase coexistence
- Author
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Jing Gao, Ke Wang, Jing-Feng Li, Longtu Li, Zhen Zhou, Xiaowen Zhang, Dong Yang, Qing Liu, Kai-Yang Lee, Manuel Hinterstein, Yichi Zhang, and Andrew J Studer
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Piezoelectric coefficient ,Materials science ,AcademicSubjects/SCI00010 ,Materials Science ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Distortion ,Lattice (order) ,Ceramic ,Engineering & allied operations ,lead-free ,Flexibility (engineering) ,Multidisciplinary ,piezoelectricity ,structural flexibility ,potassium–sodium niobite ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Engineering physics ,Piezoelectricity ,0104 chemical sciences ,temperature stability ,visual_art ,visual_art.visual_art_medium ,Curie temperature ,ddc:620 ,AcademicSubjects/MED00010 ,0210 nano-technology ,Research Article - Abstract
Due to growing concern for the environment and human health, searching for high-performance lead-free piezoceramics has been a hot topic of scientific and industrial research. Despite the significant progress achieved toward enhancing piezoelectricity, further efforts should be devoted to the synergistic improvement of piezoelectricity and its thermal stability. This study provides new insight into these topics. A new KNN-based lead-free ceramic material is presented, which features a large piezoelectric coefficient (d33) exceeding 500 pC/N and a high Curie temperature (Tc) of ∼200°C. The superior piezoelectric response strongly relies on the increased composition-induced structural flexibility due to lattice softening and decreased unit cell distortion. In contrast to piezoelectricity anomalies induced via polymorphic transition, this piezoelectricity enhancement is effective within a broad temperature range rather than a specific small range. In particular, a hierarchical domain architecture composed of nano-sized domains along the submicron domains was detected in this material system, which further contributes to the high piezoelectricity.
- Published
- 2020
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9. Magnetic and Structural Transitions Tuned through Valence Electron Concentration in Magnetocaloric Mn(Co1–xNix)Ge
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Stewart J Campbell, Wayne D. Hutchison, Jianli Wang, Andrew J Studer, and Qing Yon Ren
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Materials science ,Condensed matter physics ,Magnetism ,General Chemical Engineering ,Fermi surface ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferromagnetism ,0103 physical sciences ,Materials Chemistry ,Magnetic refrigeration ,Density of states ,Antiferromagnetism ,Orthorhombic crystal system ,010306 general physics ,0210 nano-technology ,Valence electron - Abstract
The structural and magnetic properties of magnetocaloric Mn(Co1–xNix)Ge compounds have been studied. Two responses to the increase of valence electron concentration on substitution of Ni (3d84s2) for Co (3d74s2) in the orthorhombic phase (Pnma) are proposed: expansion of unit-cell volume and redistribution of valence electrons. We present experimental evidence for electronic redistribution associated with the competition between magnetism and bonding. This competition in turn leads to complex dependences of the reverse martensitic transformation temperature TM (orthorhombic to hexagonal (P63/mmc)) and the magnetic structures on the Ni concentration. Magnetic transitions from ferromagnetic structures below x = 0.50 to noncollinear spiral antiferromagnetic structures above x = 0.55 at low temperature (e.g., 5 K) are induced by modification of the density of states at the Fermi surface due to the redistribution of valence electrons. TM is found to decrease initially with increasing Ni content and then increa...
- Published
- 2018
10. Controllable isotropic thermal expansion in series of designed magnetocaloric materials HoCo2Mn (x = 0–1.0)
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Chun Sheng Fang, Wei Wang, Andrew J Studer, Qinfen Gu, Jianli Wang, Wayne D. Hutchison, and Jinkui Zhao
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Materials science ,Condensed matter physics ,Mechanical Engineering ,Doping ,Neutron diffraction ,Isotropy ,Metals and Alloys ,chemistry.chemical_element ,02 engineering and technology ,Manganese ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Thermal expansion ,0104 chemical sciences ,chemistry ,Negative thermal expansion ,Mechanics of Materials ,Materials Chemistry ,Magnetic refrigeration ,Curie temperature ,0210 nano-technology - Abstract
We detected a crossover from negative to positive thermal expansion with increasing Mn in HoCo2Mnx below the Curie temperature through high quality neutron diffraction measurements from 5 K to 400 K. Almost isotropic zero thermal expansion with coefficient of thermal expansion αl = −4.894 × 10−7/K was achieved over a large range of temperature from 5 K to TC = 225 K in the compound HoCo2Mn0.5. While the addition of manganese was shown to change the temperature dependence of the lattice, it was also noted that the Curie temperature rose significantly from 88 K in HoCo2 to 253 K in HoCo2Mn providing a hope for a room temperature transition in similar doping series materials.
- Published
- 2021
11. First-order magneto-structural transition and magnetocaloric effect in Mn(Co0.96Fe0.04)Ge
- Author
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Wayne D. Hutchison, Jianli Wang, Qing Yon Ren, Stewart J Campbell, and Andrew J Studer
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010302 applied physics ,Materials science ,Magnetic structure ,Condensed matter physics ,Mechanical Engineering ,Neutron diffraction ,Metals and Alloys ,Analytical chemistry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Paramagnetism ,Magnetization ,Ferromagnetism ,Mechanics of Materials ,0103 physical sciences ,Materials Chemistry ,Magnetic refrigeration ,Curie temperature ,Orthorhombic crystal system ,0210 nano-technology - Abstract
The magnetic properties and magnetic structure of an as-prepared Mn(Co0.96Fe0.04)Ge sample has been investigated by powder neutron diffraction as well as X-ray diffraction and magnetisation measurements. The sample has a ferromagnetic structure in the low-temperature orthorhombic phase and a magneto-structural transition at 299 (1) K to the high-temperature paramagnetic hexagonal phase. This transition occurs at a higher temperature than for as-prepared (Mn0.96Fe0.04)CoGe (TM = 239 (1) K). Increased occupancy by Fe of the Co (4c) site rather than the Mn (4c) site results in this smaller suppression of the structural transition temperature away from that of undoped MnCoGe. It was found that chemical pressure increased the Curie temperature T C orth in the orthorhombic phase from 355 (5) K in Mn(Co0.96Fe0.04)Ge to 379 (6) K in MnCoGe. Mn(Co0.96Fe0.04)Ge exhibits a large magnetocaloric effect around the magneto-structural transition, − Δ S m peak = 11 (2) J kg−1 K−1 and RC = 187 (30) J kg−1 with μ0ΔH = 5 T. The magneto-structural transition is a first order transition as demonstrated by master curve analysis.
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- 2017
12. High-Temperature Phase Equilibria of Duplex Stainless Steels Assessed with a Novel In-Situ Neutron Scattering Approach
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Sten Wessman, Andrew J Studer, Niklas Pettersson, and Staffan Hertzman
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010302 applied physics ,In situ ,Austenite ,Materials science ,Metallurgy ,Metals and Alloys ,Solid-state ,02 engineering and technology ,Neutron scattering ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Mechanics of Materials ,Duplex (building) ,Ferrite (iron) ,0103 physical sciences ,0210 nano-technology - Abstract
Duplex stainless steels are designed to solidify with ferrite as the parent phase, with subsequent austenite formation occurring in the solid state, implying that, thermodynamically, a fully ferrit ...
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- 2017
13. Reversibility of spin-induced electric polarization in multiferroic hexaferrites
- Author
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Young Sun, Congli He, Shouguo Wang, Shipeng Shen, Xinzhi Liu, Andrew J Studer, and Yisheng Chai
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Materials science ,Condensed matter physics ,Neutron diffraction ,02 engineering and technology ,Spin current ,021001 nanoscience & nanotechnology ,Rotation ,01 natural sciences ,Magnetic field ,Polarization density ,0103 physical sciences ,Multiferroics ,010306 general physics ,0210 nano-technology ,Spin (physics) - Abstract
Hexaferrites with noncollinear conical magnetic structures are among the most interesting and promising single-phase multiferroics. One puzzle remaining unsolved is why the spin-induced electric polarization can be either reversible or nonreversible by applying magnetic fields. We have unraveled a solution to this puzzle by a systematic study in the multiferroic hexaferrite ${\mathrm{Ba}}_{0.3}{\mathrm{Sr}}_{1.7}{\mathrm{Co}}_{2}{\mathrm{Fe}}_{11}{\mathrm{AlO}}_{22}$ where the electric polarization is reversible at low temperatures but nonreversible at high temperatures. Neutron diffraction results reveal that the rotation of spin cones with applied $ab$-plane magnetic field takes distinct paths at 150 and 305 K: in-plane and out-of-plane rotation, respectively. A theoretical analysis based on the spin current model confirms that the reversal of electric polarization is caused by the in-plane rotation. Our study clarifies the mechanism underlying the reversibility of spin-induced electric polarization in multiferroic hexaferrites.
- Published
- 2019
14. Simultaneous tuning of magnetocrystalline anisotropy and spin reorientation transition via Cu substitution in Mn-Ni-Ga magnets for nanoscale biskyrmion formation
- Author
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Yurong You, Jiaxuan Tang, Zhenxiang Cheng, Jianli Wang, Andrew J Studer, Hang Li, Yuanyuan Gong, Feng Xu, Guizhou Xu, Wenhong Wang, Xuefei Miao, Hongguo Zhang, and Zhipeng Hou
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Materials science ,Condensed matter physics ,Magnetic structure ,Skyrmion ,Exchange interaction ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Magnetocrystalline anisotropy ,01 natural sciences ,Helicity ,Condensed Matter::Materials Science ,Transmission electron microscopy ,0103 physical sciences ,Curie temperature ,010306 general physics ,0210 nano-technology ,Anisotropy - Abstract
Skyrmions with multiple helicity or topology in centrosymmetric crystals are intriguing magnetic-domain objects due to their diverse dynamics under external stimuli. Here we illustrate how the two key gradients of magnetocrystalline anisotropy (MCA) and spin reorientation transition (SRT) affect the skyrmion formation and topology by Cu substitution in the biskyrmion-host MnNiGa alloy. The MCA and SRT are simultaneously tuned in a large scope, while the original high Curie temperature (${T}_{C}$) is retained. Detailed neutron-scattering studies revealed the construction of a noncollinear canted magnetic structure below the SRT temperature (${T}_{\mathrm{SR}}$), which effectively correlates the SRT with the evolution of the MCA, as well as the exchange interaction. The Cu substitution raises the ${T}_{\mathrm{SR}}$ to merge with the ${T}_{\mathrm{C}}$, and meanwhile, reduces the $c$-axis anisotropy. Lorentz transmission electron microscopy revealed the formation of stacked biskyrmions from above room temperature to lower temperatures in $\mathrm{MnN}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{u}}_{x}\mathrm{Ga}\phantom{\rule{0.28em}{0ex}}(x=0--0.3)$ in the presence of proper MCA. Micromagnetic simulations further confirmed the great effect of uniaxial anisotropy on the stabilization of biskyrmions. Our work has helped clarify the evolution of magnetic structures and their correlation to the SRT, providing an account of the effect of MCA and exchange interaction on the biskyrmion formation.
- Published
- 2019
15. Determining fundamental properties from diffraction: Electric field induced strain and piezoelectric coefficient
- Author
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Sophia Esslinger, Julia Glaum, Andrew J Studer, Kai-Yang Lee, Manuel Hinterstein, Mark Hoffman, and Michael J. Hoffmann
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Diffraction ,Materials science ,Piezoelectric coefficient ,Condensed matter physics ,Strain (chemistry) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,Condensed Matter::Materials Science ,Phase (matter) ,Electric field ,0103 physical sciences ,Crystallite ,010306 general physics ,0210 nano-technology ,Actuator - Abstract
Neutron powder diffraction was used in operando to determine the macroscopic strain and piezoelectric coefficient as a function of applied electric field in a technically relevant actuator material. We were able to individually investigate the two coexisting phases in the material and reveal the origin of maximized strain at phase boundaries. Insight into the strain mechanisms gives evidence that, on average, the classic inverse piezoelectric effect does not apply for polycrystalline materials.
- Published
- 2019
16. Magnetic phase diagram of the frustrated spin chain compound linarite PbCuSO4(OH)2 as seen by neutron diffraction and H1 -NMR
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Satoshi Nishimoto, Stefan-Ludwig Drechsler, Fabrice Bert, G. Bastien, L. Heinze, E. Kermarrec, H. Rosner, J.-U. Hoffmann, B. Ouladdiaf, Stefan Süllow, B. Ryll, Andrew J Studer, U. K. Rößler, Bernd Büchner, A. U. B. Wolter, Kirrily C. Rule, Philippe Mendels, and Manfred Reehuis
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Physics ,Magnetic moment ,Condensed matter physics ,media_common.quotation_subject ,Neutron diffraction ,Frustration ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,Exchange bias ,Ferromagnetism ,0103 physical sciences ,engineering ,Linarite ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,media_common ,Phase diagram - Abstract
We report on a detailed neutron diffraction and $^{1}\mathrm{H}$-NMR study on the frustrated spin-1/2 chain material linarite, ${\mathrm{PbCuSO}}_{4}{(\mathrm{OH})}_{2}$, where competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions lead to frustration. From the magnetic Bragg peak intensity studied down to 60 mK, the magnetic moment per Cu atom is obtained within the whole magnetic phase diagram for $H\ensuremath{\parallel}b$ axis. Further, we establish the detailed configurations of the shift of the SDW propagation vector in phase V with field and temperature. Finally, combining our neutron diffraction results with those from a low-temperature/high-field NMR study, we find an even more complex phase diagram close to the quasisaturation field suggesting that bound two-magnon excitations are the lowest energy excitations close to and in the quasisaturation regime. Qualitatively and semiquantitatively, we relate such behavior to $XYZ$ exchange anisotropy and contributions from the Dzyaloshinsky-Moriya interaction to affect the magnetic properties of linarite.
- Published
- 2019
17. Evolution of the magnetic structure of TbRu2Al10 in applied field
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Andrew J Studer, R. White, Wayne D. Hutchison, and Toshio Mizushima
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Materials science ,Magnetic moment ,Condensed matter physics ,Magnetic structure ,Field (physics) ,Mechanical Engineering ,Metals and Alloys ,02 engineering and technology ,Square wave ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,Mechanics of Materials ,Duty cycle ,0103 physical sciences ,Materials Chemistry ,Pulse wave ,010306 general physics ,0210 nano-technology ,Single crystal - Abstract
TbRu 2 Al 10 is found to undergo two magnetic phase transitions as a function of temperature and three as a function of applied field at low temperature. The Tb 3+ magnetic moments order antiferromagnetically along the c -axis at 15.0(3) K, with an incommensurate sinusoidally modulated structure with a propagation vector of k = (0, 0.759(1), 0). At 6.5(3) K the structure switches to square wave order. Analysis of single crystal TbRu 2 Al 10 has revealed that this square wave structure is altered to a ‘pulse wave’ on application of a 1.30 T magnetic field along the c -axis, with two in fifty of the magnetic moments across the structure changing direction to be aligned parallel with the direction of the field. At 1.85 T a further three moments flip, leading to a duty cycle of 60% and resulting in a total change of one in ten moments from the starting square wave structure.
- Published
- 2016
18. Extreme compressibility in LnFe(CN)6 coordination framework materials via molecular gears and torsion springs
- Author
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Gordon J. Kearley, Cameron J. Kepert, Andrew J Studer, Vanessa K. Peterson, and Samuel G. Duyker
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chemistry.chemical_classification ,Flexibility (anatomy) ,Chemistry ,General Chemical Engineering ,Thermodynamics ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Crystal engineering ,01 natural sciences ,Torsion spring ,0104 chemical sciences ,Coordination complex ,Mechanism (engineering) ,medicine.anatomical_structure ,Deformation mechanism ,Compressibility ,medicine ,Metal-organic framework ,0210 nano-technology - Abstract
The mechanical flexibility of coordination frameworks can lead to a range of highly anomalous structural behaviours. Here, we demonstrate the extreme compressibility of the LnFe(CN)6 frameworks (Ln = Ho, Lu or Y), which reversibly compress by 20% in volume under the relatively low pressure of 1 GPa, one of the largest known pressure responses for any crystalline material. We delineate in detail the mechanism for this high compressibility, where the LnN6 units act like torsion springs synchronized by rigid Fe(CN)6 units performing the role of gears. The materials also show significant negative linear compressibility via a cam-like effect. The torsional mechanism is fundamentally distinct from the deformation mechanisms prevalent in other flexible solids and relies on competition between locally unstable metal coordination geometries and the constraints of the framework connectivity, a discovery that has implications for the strategic design of new materials with exceptional mechanical properties.
- Published
- 2016
19. Non-zero spontaneous magnetic moment along crystalline b-axis for rare earth orthoferrites
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Alison J. Edwards, Christopher Richardson, Josip Horvat, Mohanad Hazim Mohammed, Shixun Cao, Andrew J Studer, Zhenxiang Cheng, and Kirrily C. Rule
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010302 applied physics ,Materials science ,Magnetic moment ,Magnetic structure ,Spintronics ,Condensed matter physics ,Spins ,Magnetometer ,Neutron diffraction ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,Multiferroics ,0210 nano-technology ,Spin (physics) - Abstract
Rare earth orthoferrites demonstrate great application potentials in spintronics and optical devices due to their multiferroic and magnetooptical properties. In RFeO3, magnetic R3+ undergo a spontaneous spin reorientation in a temperature range determined by R (rare earth), where the magnetic structure changes from Γ2 to Γ4. The b-axis component of their magnetic moment, Mb, is reported in numerous neutron diffraction studies to remain zero at all temperatures. More sensitive magnetometer measurements reveal a small non-zero Mb, which is minute above ∼200 K. Mb increases with cooling and reaches values of ∼10–3 μB/f.u. at temperatures within or below the spin reorientation temperatures. Our results can be explained by assuming the Fe3+ spins as the origin of non-zero Mb, while R3+ spins suppress Mb. The representation analysis of point groups shows that non-zero Mb is associated with a small admixture of the Γ3 phase to Γ2 or Γ4. Such a mixing of the three magnetic phases requires at least a fourth order of the spin Hamiltonian for RFeO3 to describe the non-zero Mb.
- Published
- 2020
20. Spin dynamics and magnetoelectric coupling mechanism of Co4Nb2O9
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Wei Ren, Garry J. McIntyre, Jason Gardner, Michel Kenzelmann, Yiming Cao, Paolo Imperia, G. Davidson, Nicolas Gauthier, Andrew J Studer, Guochu Deng, Clemens Ulrich, Kirrily C. Rule, and Shixun Cao
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Neutron powder diffraction ,Physics ,Spin dynamics ,Magnetic structure ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Inelastic neutron scattering ,Crystallography ,Coupling effect ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Spin (physics) ,Anisotropy - Abstract
Neutron powder diffraction experiments reveal that $\mathrm{C}{\mathrm{o}}_{4}\mathrm{N}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ forms a noncollinear in-plane magnetic structure with $\mathrm{C}{\mathrm{o}}^{2+}$ moments lying in the $ab$ plane. The spin-wave excitations of this magnet were measured by using inelastic neutron scattering and soundly simulated by a dynamic model involving nearest- and next-nearest-neighbor exchange interactions, in-plane anisotropy, and the Dzyaloshinskii-Moriya interaction. The in-plane magnetic structure of $\mathrm{C}{\mathrm{o}}_{4}\mathrm{N}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ is attributed to the large in-plane anisotropy, while the noncollinearity of the spin configuration is attributed to the Dzyaloshinskii-Moriya interaction. The high magnetoelectric coupling effect of $\mathrm{C}{\mathrm{o}}_{4}\mathrm{N}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ in fields can be explained by its special in-plane magnetic structure.
- Published
- 2018
21. Critical role of the coupling between the octahedral rotation andA-site ionic displacements inPbZrO3-based antiferroelectric materials investigated byin situneutron diffraction
- Author
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Zhuo Xu, Yun Liu, Teng Lu, Hua Chen, Dehong Yu, S. S. Islam, Andrew J Studer, Yujun Feng, and Raymond Withers
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Phase transition ,Materials science ,Neutron diffraction ,Ionic bonding ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Ferroelectricity ,Orientation (vector space) ,Crystallography ,Octahedron ,Phase (matter) ,0103 physical sciences ,010306 general physics ,0210 nano-technology - Abstract
This in situ neutron-diffraction study on antiferroelectric (AFE) $\mathrm{P}{\mathrm{b}}_{0.99}(\mathrm{N}{\mathrm{b}}_{0.02}\mathrm{Z}{\mathrm{r}}_{0.65}\mathrm{S}{\mathrm{n}}_{0.28}\mathrm{T}{\mathrm{i}}_{0.05}){\mathrm{O}}_{3}$ polycrystalline materials describes systematic structural and associated preferred orientation changes as a function of applied electric field and temperature. It is found that the pristine AFE phase can be poled into the metastable ferroelectric (FE) phase at room temperature. At this stage, both AFE and FE phases consist of modes associated with octahedral rotation and $A$-site ionic displacements. The temperature-induced phase transition indicates that the octahedral rotation and ionic displacements are weakly coupled in the room-temperature FE phase and decoupled in the high-temperature FE phase. However, both temperature and $E$-field-induced phase transitions between the AFE and high-temperature FE phase demonstrate the critical role of coupling between octahedral rotation and $A$-site ionic displacements in stabilizing the AFE structure, which provides not only experimental evidence to support previous theoretical calculations, but also an insight into the design and development of AFE materials. Moreover, the associated preferred orientation evolution in both AFE and FE phases is studied during the phase transitions. It is found that the formation of the preferred orientation can be controlled to tune the samples' FE and AFE properties.
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- 2017
22. Tuning the magnetic and structural transitions in TbCo2Mnx compounds
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Zhenxiang Cheng, Wayne D. Hutchison, Chunsheng Fang, Fang Hong, M. F Din, Jianli Wang, Shi Xue Dou, Andrew J Studer, and Justin A. Kimpton
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010302 applied physics ,Diffraction ,Materials science ,Condensed matter physics ,Neutron diffraction ,Intermetallic ,Order (ring theory) ,02 engineering and technology ,Crystal structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetization ,Magnet ,0103 physical sciences ,0210 nano-technology ,Critical exponent - Abstract
The wide ranging magnetic behavior in intermetallic compounds continues to attract broad interest. Effective control of their magnetic properties is of great importance for fundamental research and potential applications. In this work the structural and magnetic properties of $\mathrm{TbC}{\mathrm{o}}_{2}\mathrm{M}{\mathrm{n}}_{x}$ compounds are studied by a combination of temperature dependent synchrotron x-ray diffraction, neutron powder diffraction, specific heat, and magnetic measurements. Magnetization measurements show that the addition of Mn can modify the magnetic behavior significantly: first, the magnetic transition temperatures increase from \ensuremath{\sim}227 K to 332 K with $x=0.0\phantom{\rule{0.28em}{0ex}}\mathrm{to}\phantom{\rule{0.28em}{0ex}}0.3$; secondly, the nature of the magnetic transitions change from the first order to second order, as identified by three methods (Banerjee criterion, master curves of magnetic entropy changes, and detailed crystal structure analysis through neutron diffraction). Both synchrotron x-ray diffraction and neutron diffraction confirm that a structural transition, from cubic $Fd\overline{3}m$ to rhombohedral $R\overline{3}m$ on cooling, occurred accompanying the magnetic transition. To further clarify the nature of the second order magnetic phase transitions, we have carried out a detailed critical exponent analysis. The derived critical exponents are close to the theoretical prediction from the mean-field model, indicating the magnetic interactions are long range. This work benefits our general understanding of magnetic interactions in intermetallic compounds and provides guidance to design a functional magnetic material for room temperature magnetic devices.
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- 2017
23. Hidden spin-order-induced room-temperature ferroelectricity in a peculiar conical magnetic structure
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Andrew J Studer, Shipeng Shen, Dashan Shang, Frank Klose, Kun Zhai, Yisheng Chai, Xinzhi Liu, Young Sun, Kirrily C. Rule, Yuntao Liu, Liqin Yan, and Dongfeng Chen
- Subjects
Physics ,Condensed matter physics ,Magnetic structure ,Neutron diffraction ,Order (ring theory) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Magnetic field ,Condensed Matter::Materials Science ,Polarization density ,0103 physical sciences ,Multiferroics ,010306 general physics ,0210 nano-technology ,Spin-½ - Abstract
A novel mechanism of spin-induced ferroelectricity is unraveled in the alternating longitudinal conical (ALC) magnetic structure. Because the noncollinear ALC structure possesses a $c$-axis component with collinear \ensuremath{\uparrow}--\ensuremath{\uparrow}--\ensuremath{\downarrow}--\ensuremath{\downarrow} spin order, spin-driven ferroelectricity along the $c$ axis due to the exchange striction mechanism is predicted. Our experiments verify this prediction in the Y-type hexaferrite $\mathrm{B}{\mathrm{a}}_{0.3}\mathrm{S}{\mathrm{r}}_{1.7}\mathrm{C}{\mathrm{o}}_{2}\mathrm{F}{\mathrm{e}}_{11}\mathrm{Al}{\mathrm{O}}_{22}$, where ferroelectricity along the $c$ axis is observed up to room temperature. Neutron diffraction data clearly reveal the ALC phase and its evolution with magnetic fields. The $c$-axis electric polarization can be well modulated by applying either $ab$-plane or $c$-axis magnetic fields, even at 305 K. This kind of spin-induced ferroelectricity associated with the ALC magnetic structure provides a new resource of type II multiferroics.
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- 2017
24. Large easy-plane anisotropy induced spin reorientation in magnetoelectric materials (Co4−x Mn x )Nb2O9
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Zhenjie Feng, Youshuang Yu, Clemens Ulrich, Wei Ren, Yousef Kareri, Guochu Deng, Shixun Cao, James R. Hester, Garry J. McIntyre, Andrew J Studer, and Yiming Cao
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Materials science ,Condensed matter physics ,Magnetic moment ,Magnetic structure ,Rietveld refinement ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Condensed Matter::Materials Science ,Magnetization ,0103 physical sciences ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,010306 general physics ,0210 nano-technology ,Spin (physics) ,Anisotropy ,Néel temperature - Abstract
Neutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co4-x Mn x )Nb2O9 (x = 0, 1, 2, 3, 3.5, 3.9, 3.95 and 4) from base temperature to above their Neel temperatures. Their magnetic structures were analysed by using the irreducible representation analysis and Rietveld refinement method. Similar to Co4Nb2O9, the compounds with x ⩽ 3.9 have noncollinear in-plane magnetic structures (Γ6) with magnetic moments lying purely in the ab plane with certain canting angles. Mn4Nb2O9 has a collinear antiferromagnetic structure (Γ2) with magnetic moments aligning along the c axis. The compound of x = 3.95 shows two magnetic phases in the magnetization, which was confirmed to have the Γ2 magnetic structure above 60 K and develop a second Γ6 local phase in addition to the main Γ2 phase due to doping. This study indicates 2.5 at% Co2+ doping is sufficient to alter the collinear easy-axis magnetic structure of Mn4Nb2O9 into the noncollinear easy-plane magnetic structure, which is attributed to the large easy-plane anisotropy of Co2+ and relative small Ising-like anisotropy of Mn2+. The doping effects on the Neel temperature and occupancy are also discussed.
- Published
- 2019
25. Electric-field-induced AFE-FE transitions and associated strain/preferred orientation in antiferroelectric PLZST
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Andrew J Studer, Lasse Noren, Raymond Withers, Yujun Feng, Wanbiao Hu, Zhou Xu, Yun Liu, Teng Lu, Dehong Yu, Hua Chen, and Bethany R. McBride
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010302 applied physics ,Phase transition ,Work (thermodynamics) ,Multidisciplinary ,Materials science ,Condensed matter physics ,Strain (chemistry) ,Neutron diffraction ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,Bioinformatics ,01 natural sciences ,Article ,Electric field ,Orientation (geometry) ,0103 physical sciences ,Antiferroelectricity ,0210 nano-technology - Abstract
Electric-field-induced, antiferroelectric-ferroelectric (AFE-FE) phase transitions are common for AFE materials. To date, the strain and preferred orientation evolution as well as the role of the intermediate FE state during the successive AFE-FE-AFE phase transitions has not been clear. To this end, we have herein studied a typical AFE Pb0.97La0.02(Zr0.56Sn0.33Ti0.11)O3 (PLZST) material using in-situ neutron diffraction. It is striking that the AFE-FE phase transition is not fully reversible: in the electric-field-induced FE state, the induced strain exhibits an elliptical distribution, which in turn leads to significant preferred orientation in the final AFE state after withdrawal of the applied electric-field. The ω-dependent neutron diffraction patterns show clear evidence of the induced strain distribution and associated preferred orientation arising from the AFE-FE phase transition. The current work also provides an explanation for several temperature and electric-field dependent dielectric anomalies as well as unrecovered strain change which appear in AFE materials after exposure to sufficiently high electric fields.
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- 2016
- Full Text
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26. Complex Field-Induced States in LinaritePbCuSO4(OH)2with a Variety of High-Order Exotic Spin-Density Wave States
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J.-U. Hoffmann, Satoshi Nishimoto, M. Schäpers, Stefan Süllow, B. Willenberg, Kirrily C. Rule, Andrew J Studer, Manfred Reehuis, Anja U. B. Wolter, S.-L. Drechsler, B. Ouladdiaf, and Bernd Büchner
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Physics ,Condensed matter physics ,media_common.quotation_subject ,Neutron diffraction ,General Physics and Astronomy ,Frustration ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,Ferromagnetism ,Critical point (thermodynamics) ,0103 physical sciences ,engineering ,Linarite ,Spin density wave ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Ground state ,media_common - Abstract
Low-temperature neutron diffraction and NMR studies of field-induced phases in linarite are presented for magnetic fields H∥b axis. A two-step spin-flop transition is observed, as well as a transition transforming a helical magnetic ground state into an unusual magnetic phase with sine-wave-modulated moments ∥H. An effective J[over ˜]_{1}-J[over ˜]_{2} single-chain model with a magnetization-dependent frustration ratio α_{eff}=-J[over ˜]_{2}/J[over ˜]_{1} is proposed. The latter is governed by skew interchain couplings and shifted to the vicinity of the ferromagnetic critical point. It explains qualitatively the observation of a rich variety of exotic longitudinal collinear spin-density wave, SDW_{p}, states (9≥p≥2).
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- 2016
27. LiNbO3-type InFeO3: Room-temperature polar magnet without second-order Jahn-Teller active ions
- Author
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Katsuhisa Tanaka, Andrew J Studer, Christopher S. Knee, Masafumi Fukuzumi, Koji Fujita, Olivier Hernandez, Naoaki Hayashi, William Lafargue-Dit-Hauret, Takahiro Kawamoto, Pascal Manuel, Hirofumi Akamatsu, Xavier Rocquefelte, Ikuya Yamada, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan, Department of Energy Systems Eng., Osaka Prefecture University, Sakai, Osaka 599-8531, Japan, affiliation inconnue, Institut des Sciences Chimiques de Rennes (ISCR), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Research Institute for Production Development [Kyoto], Pennsylvania State University (Penn State), Penn State System, Hyogo Prefectural Institute of Technology, STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC), Australian Nuclear Science and Technology Organisation [Australie] (ANSTO), University of Gothenburg (GU), 15J08052, JSPS, Japan Society for the Promotion of Science London, Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), and ⊥Research Institute for Production Development, Shimogamo-Morimoto-cho 15, Sakyo-ku, Kyoto 606-0805, Japan
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Materials science ,Jahn-Teller effect ,General Chemical Engineering ,Jahn–Teller effect ,02 engineering and technology ,010402 general chemistry ,Iron compounds ,Perovskite ,01 natural sciences ,Structure analysis ,Ferromagnetic behaviors ,Antiferromagnetism ,Polar structures ,Polarization ,Materials Chemistry ,Electric polarization ,Barium compounds ,[CHIM]Chemical Sciences ,Multiferroics ,Metal ions ,Antiferromagnetic orderings ,Perovskite (structure) ,Elevated temperature ,Condensed matter physics ,Ferroelectric materials ,Magnetic studies ,General Chemistry ,Transition metals ,[CHIM.MATE]Chemical Sciences/Material chemistry ,021001 nanoscience & nanotechnology ,Ferroelectricity ,0104 chemical sciences ,Polarization density ,Metals ,Positive ions ,Magnets ,Density functional theory ,Polar ,Orthorhombic crystal system ,Orthorhombic perovskite ,0210 nano-technology ,Transition metal compounds ,Bismuth compounds - Abstract
International audience; Great effort has been devoted to developing single-phase magnetoelectric multiferroics, but room-temperature coexistence of large electric polarization and magnetic ordering still remains elusive. Our recent finding shows that such polar magnets can be synthesized in small-tolerance-factor perovskites AFeO3 with unusually small cations at the A-sites, which are regarded as having a LiNbO3-type structure (space group R3c). Herein, we experimentally reinforce this finding by preparing a novel room-temperature polar magnet, LiNbO3-type InFeO3. This compound is obtained as a metastable quench product from an orthorhombic perovskite phase stabilized at 15 GPa and an elevated temperature. The structure analyses reveal that the polar structure is characterized by displacements of In3+ (d10) and Fe3+ (d5) ions along the hexagonal c-axis (pseudocubic [111] axis) from their centrosymmetric positions, in contrast to well-known perovskite ferroelectrics (e.g., BaTiO3, PbTiO3, and BiFeO3) where d0 transition-metal ions and/or 6s2 lone-pair cations undergo polar displacements through the so-called second-order Jahn-Teller (SOJT) distortions. Using density functional theory calculations, the electric polarization of LiNbO3-type InFeO3 is estimated to be 96 μC/cm2 along the c-axis, comparable to that of an isostructural and SOJT-active perovskite ferroelectric, BiFeO3 (90-100 μC/cm2). Magnetic studies demonstrate weak ferromagnetic behavior at room temperature, as a result of the canted G-type antiferromagnetic ordering of Fe3+ moments below TN ∼ 545 K. The present work shows the functional versatility of small-tolerance-factor perovskites and provides a useful guide for the synthesis and design of room-temperature polar magnets. © 2016 American Chemical Society.
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- 2016
28. Piezoelectricity and rotostriction through polar and non-polar coupled instabilities in bismuth-based piezoceramics
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Matias Acosta, Manuel Hinterstein, Claudio Cazorla, Alexander Zintler, Mark Hoffman, Andrew J Studer, Jürgen Rödel, Julia Glaum, Hans-Joachim Kleebe, Wolfgang Donner, and Ljubomira Ana Schmitt
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010302 applied physics ,Superconductivity ,Technology ,Multidisciplinary ,Materials science ,Condensed matter physics ,Neutron diffraction ,Ionic bonding ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Piezoelectricity ,Article ,Tetragonal crystal system ,Phase (matter) ,0103 physical sciences ,Multiferroics ,0210 nano-technology ,ddc:600 - Abstract
Coupling of order parameters provides a means to tune functionality in advanced materials including multiferroics, superconductors, and ionic conductors. We demonstrate that the response of a frustrated ferroelectric state leads to coupling between order parameters under electric field depending on grain orientation. The strain of grains oriented along a specific crystallographic direction, ⟨h00⟩, is caused by converse piezoelectricity originating from a ferrodistortive tetragonal phase. For ⟨hhh⟩ oriented grains, the strain results from converse piezoelectricity and rotostriction, as indicated by an antiferrodistortive instability that promotes octahedral tilting in a rhombohedral phase. Both strain mechanisms combined lead to a colossal local strain of (2.4 ± 0.1) % and indicate coupling between oxygen octahedral tilting and polarization, here termed “rotopolarization”. These findings were confirmed with electromechanical experiments, in situ neutron diffraction, and in situ transmission electron microscopy in 0.75Bi1/2Na1/2TiO3-0.25SrTiO3. This work demonstrates that polar and non-polar instabilities can cooperate to provide colossal functional responses This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0
- Published
- 2016
- Full Text
- View/download PDF
29. Phase fractions, transition and ordering temperatures in TiAl–Nb–Mo alloys: An in- and ex-situ study
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Laura M. Droessler, Helmut Clemens, Thomas Schmoelzer, Thomas Buslaps, Ian J. Watson, Andrew J Studer, Gerald A. Zickler, Klaus-Dieter Liss, and Wilfried Wallgram
- Subjects
010302 applied physics ,Diffraction ,Phase transition ,Materials science ,Mechanical Engineering ,Neutron diffraction ,Alloy ,Metals and Alloys ,Analytical chemistry ,Intermetallic ,02 engineering and technology ,General Chemistry ,Calorimetry ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystallography ,Mechanics of Materials ,Phase (matter) ,0103 physical sciences ,Materials Chemistry ,engineering ,Metallography ,0210 nano-technology - Abstract
Intermetallic γ-TiAl based alloys of the TNM™ alloy family attain their excellent processing characteristics by a high β-phase content present at hot-working temperatures. Subsequent to hot-working the β-phase content is decreased by a heat treatment step performed at temperatures where the β-phase fraction exhibits a minimum. In this study, in- and ex-situ experiments were conducted on three alloys with different contents of β/β 0 stabilizing elements. The course of phase fractions as a function of temperature as well as phase transition temperatures were determined by means of in-situ high-energy X-ray diffraction experiments. Additionally, dynamic scanning calorimetry investigations were performed to obtain complementary data on the transition temperatures. Quantitative metallography was conducted on heat treated and quenched specimens to acquire additional information on the dependence of the phase fractions on temperature. By neutron diffraction experiments the ordering temperatures of the constituent phases were determined. It was shown that the experiments yielded consistent results which differ significantly from ThermoCalc simulations for which a commercial TiAl database was used. The differences between the experimental results and the thermodynamic predictions are discussed.
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- 2010
30. Low temperature magnetic properties of Nd2Ru2O7
- Author
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Shinichiro Asai, Lieh-Jeng Chang, Andrew J Studer, Takatsugu Masuda, Jianguo Chen, R. Aldus, S. T. Ku, W. T. Lee, Martin R. Lees, P. Imperia, Dinesh Kumar, and S. W. Chen
- Subjects
Materials science ,Spin glass ,Strongly Correlated Electrons (cond-mat.str-el) ,Magnetic moment ,Condensed matter physics ,Magnetic structure ,Neutron diffraction ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Magnetic susceptibility ,Condensed Matter - Strongly Correlated Electrons ,Ferromagnetism ,0103 physical sciences ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,010306 general physics ,0210 nano-technology ,Ground state ,QC - Abstract
We present magnetic susceptibility, heat capacity, and neutron diffraction measurements of polycrystalline Nd2Ru2O7 down to 0.4 K. Three anomalies in the magnetic susceptibility measurements at 146, 21 and 1.8 K are associated with an antiferromagnetic ordering of the Ru4+ moments, a weak ferromagnetic signal attributed to a canting of the Ru4+ and Nd3+ moments, and a long-range-ordering of the Nd3+ moments, respectively. The long-range order of the Nd3+ moments was observed in all the measurements, indicating that the ground state of the compound is not a spin glass. The magnetic entropy of Rln2 accumulated up to 5 K, suggests the Nd3+ has a doublet ground state. Lattice distortions accompany the transitions, as revealed by neutron diffraction measurements, and in agreement with earlier synchrotron x-ray studies. The magnetic moment of the Nd3+ ion at 0.4 K is estimated to be 1.54(2){\mu}B and the magnetic structure is all-in all-out as determined by our neutron diffraction measurements., Comment: 21 pages, 6 figures
- Published
- 2018
31. Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution
- Author
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Zhenxiang Cheng, Jianli Wang, Fang Hong, Andrew J Studer, Binbin Yue, Chunsheng Fang, Shi Xue Dou, and Xiaolin Wang
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Spin polarization ,Spin states ,Condensed matter physics ,media_common.quotation_subject ,Neutron diffraction ,Frustration ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Spin ice ,Transition metal ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Spin (physics) ,media_common - Abstract
We studied the temperature dependent magnetic phase evolution in spin frustrated TbMnO3 affected by Fe doping via powder neutron diffraction. With the introduction of Fe (10% and 20%), the long range incommensurate magnetic orderings collapse. When the Fe content is increased to 30%, a long-range antiferromagnetic ordering develops, while a spin reorientation transition is found near 35 K from a canted G-type antiferromagnetic ordering to a collinear G-type antiferromagnetic ordering. This work demonstrates the complex magnetic interactions existing in transition metal oxides, which helps to understand the frustrated spin states in other similar systems and design magnetic materials as well.
- Published
- 2016
32. Chemical pressure effects on crystal and magnetic structures of bilayer manganites PrA2Mn2O7 (A = Sr or Ca)
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Denis Sheptyakov, Ekaterina Pomjakushina, Marisa Medarde, Andrew J Studer, M. Kenzelmann, V. Pomjakushin, Guochu Deng, Kazimierz Conder, J. S. Gardner, and Garry J. McIntyre
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Magnetic moment ,Magnetic structure ,Condensed matter physics ,Chemistry ,Bilayer ,Jahn–Teller effect ,Neutron diffraction ,General Physics and Astronomy ,Space group ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystal ,Crystallography ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,0210 nano-technology - Abstract
The crystal and magnetic structures of the bilayer manganites PrSr2Mn2O7 (PSMO) and PrCa2Mn2O7 (PCMO) have been studied by neutron powder diffraction. It was found that PSMO crystallizes in space group I4/mmm, while PCMO adopts space group Cmc21 at room temperature. The difference in the structure arises from chemical pressure induced by the Ca substitution for Sr on the A sites, which causes different Jahn-Teller distortions. In PSMO, the MnO6 octahedra suffer a small elongated distortion, while those in PCMO adopt strong compressed distortion along the axial direction. In addition, the octahedra in PCMO show a+b0c0 rotation and a0b+c+ tilting in the Glazer notation in comparison to PSMO. As a result, these two compounds adopt very different magnetic structures: The magnetic structure of PSMO is an A-type magnetic structure (Im'm'm) with propagation vector k = (0, 0, 1) and magnetic moments in the ab plane. In contrast, a C-type antiferromagnetic magnetic structure (Cm'c2′1) with the multiple propagation...
- Published
- 2016
33. The magneto-structural transition in Mn1−xFexCoGe
- Author
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Qing Yon Ren, J. M. Cadogan, Jianli Wang, Andrew J Studer, M F Din, S Munoz Perez, Stewart J Campbell, and Wayne D. Hutchison
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010302 applied physics ,Diffraction ,Acoustics and Ultrasonics ,Magnetic moment ,Chemistry ,Neutron diffraction ,02 engineering and technology ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Crystallography ,Magnetization ,Differential scanning calorimetry ,Ferromagnetism ,0103 physical sciences ,Orthorhombic crystal system ,0210 nano-technology - Abstract
Large refrigeration capacities, between 212(30) J kg−1 and 261(40) J kg−1 for a magnetic field change from 0 T to 5 T, were obtained in Mn1−x Fe x CoGe (x = 0.01, 0.02, 0.03 and 0.04) compounds. A partial magnetic phase diagram has been derived on the basis of magnetic transition and martensitic transformation temperatures determined from differential scanning calorimetry (200 K to 450 K), variable temperature x-ray diffraction (20 K to 310 K) and magnetisation measurements (5 K to 340 K; 0.01 T). Mn1−x Fe x CoGe compounds with compositions in the range x = 0.01 to 0.03 exhibit magneto-structural transitions. Neutron diffraction experiments were carried out on the Mn0.98Fe0.02CoGe sample over the temperature range of 5 K to 450 K. The diffraction patterns were analysed based on irreducible representation theory which confirms a ferromagnetic structure in the sample with an atomic magnetic moment of 3.7(1)μ B at 5 K on the Mn sublattice, oriented along the orthorhombic c axis. More significantly, a magneto-structural transition around T M ~ 297(1) K with a full width at half maximum of 29 K is demonstrated directly via neutron diffraction. Larger magnetic entropy changes are obtained for the Mn1−x Fe x CoGe (x = 0.01, 0.02 and 0.03) samples than for Mn0.96Fe0.04CoGe which has separate structural and magnetic transitions. In addition, it is noted that standard Arrott plots do not provide unambiguous insight to the nature of the magneto-structural transition in the Mn1−x Fe x CoGe compounds.
- Published
- 2016
34. Apparent critical phenomena in the superionic phase transition of Cu2-xSe
- Author
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Maxim Avdeev, Umut Aydemir, Andrew J Studer, Sergey Danilkin, G. Jeffrey Snyder, and Stephen Dongmin Kang
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Quantum phase transition ,Physics ,Phase transition ,Condensed matter physics ,Critical phenomena ,General Physics and Astronomy ,Ferroics ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,01 natural sciences ,0104 chemical sciences ,Quantum critical point ,Seebeck coefficient ,0210 nano-technology ,Phase diagram - Abstract
The superionic phase transition of Cu_(2-x)Se accompanies drastic changes in transport properties. The Seebeck coefficient increases sharply while the electrical conductivity and thermal diffusivity drops. Such behavior has previously been attributed to critical phenomena under the assumption of a continuous phase transition. However, applying Landau's criteria suggests that the transition should be first order. Using the phase diagram that is consistent with a first order transition, we show that the observed transport properties and heat capacity curves can be accounted for and modeled with good agreement. The apparent critical phenomena is shown to be a result of compositional degree-of-freedom. Understanding of the phase transition allows to explain the enhancement in the thermoelectric figure-of-merit that is accompanied with the transition.
- Published
- 2016
35. Electric-field-induced phase transitions in co-doped Pb(Zr1−xTix)O3at the morphotropic phase boundary
- Author
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Barbara Malič, Kyle G. Webber, Andrew J Studer, John E. Daniels, Julia Glaum, Yo-Han Seo, Jurij Koruza, Daniel J. Franzbach, Yichi Zhang, and Andreja Benčan
- Subjects
Morphotropic phase boundary ,Phase transition ,Phase boundary ,Materials science ,Ferroelectricity ,Field (physics) ,lcsh:Biotechnology ,PZT ,Neutron diffraction ,02 engineering and technology ,Crystal structure ,01 natural sciences ,lcsh:TP248.13-248.65 ,Electric field ,0103 physical sciences ,lcsh:TA401-492 ,General Materials Science ,010306 general physics ,Condensed matter physics ,021001 nanoscience & nanotechnology ,Crystallography ,Papers ,lcsh:Materials of engineering and construction. Mechanics of materials ,Crystallite ,0210 nano-technology ,Field induced phase transitions - Abstract
The strain- and polarization-electric field behavior was characterized at room temperature for Pb0.98Ba0.01(Zr1−xTix)0.98Nb0.02O3, 0.40 ≤ x ≤ 0.60. The investigated compositions were located in the vicinity of the morphotropic phase boundary, giving insight into the influence of crystal structure on the hysteretic ferroelectric behavior. The remanent strain of particular compositions is shown to be larger than theoretically allowed by ferroelectric switching alone, indicating the presence of additional remanent strain mechanisms. A phenomenological free energy analysis was used to simulate the effect of an applied electric field on the initial equilibrium phase. It is shown that electric-field-induced phase transitions in polycrystalline ferroelectrics can account for the experimental observations. The experimental and simulation results are contrasted to neutron diffraction measurements performed on representative compositions in the virgin and remanent states.
- Published
- 2014
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