Search

The concept of topological quantum number, or topological charge, has been used extensively to describe topological defects or solitons. Nematic liquid crystals contain both integer and half-integer topological defects, making them useful models for testing the rules that govern topological defects. Here, we investigated topological defects in nematic liquid crystals using the phase-field method. If there are no defects along a loop path, the total charge number is described by an encircled loop integral. We found that the total charge number is conserved, and the conservation of defects number is determined by a boundary during the generation and annihilation of positive–negative topological defects when the loop integral is confined. These rules can be extended to other two-dimensional systems with topological defects. [ABSTRACT FROM AUTHOR]

Nematic liquid crystals (LCs) normally contain both integer and half-integer topological charges. In this work, we investigate topological charge evolution dynamics in nematic LCs by the phase-field model. We observe the annihilation of the topological charge, and the total number of charges decreases to two cores with time evolution in a disk. A significant decrease in charges is observed during the initial evolution. The positive topological charge and negative topological charge annihilate depending on the distance between two charges, which can be treated as the interaction force. The form of interaction force is similar to Coulomb's law, but the force is inversely the distance of defects instead of the square of the distance in Coulomb's law. Therefore, the present study contributes to the understanding of topological charge evolution dynamics and provides guidance for experiments to design in nematic LCs. [ABSTRACT FROM AUTHOR]

All magnetometers using alkali atoms rely on the monochromatic light driving the optical pumping process in the D1 or D2 line to create spin-polarized atoms. In the study of a sodium (Na) magnetometer, we find that 23Na exhibits the same hyperfine structure as exhibited by the 87Rb atom but differs from Rb in terms of level splitting. The narrowly split hyperfine levels of the 23Na 3P3/2 excited state are comparable to its natural broadening (9.8 MHz). We have modeled the nearly unresolved hyperfine structure as a partially resolved multilevel system in which the absorption at each photon detuning will induce adjacent allowed transition pathways simultaneously. Thus, the corresponding optical pumping processes of 23Na and 87Rb are governed by similar rate equations but result in different redistributed populations. By numerically solving the rate equations, we demonstrate that optically pumped 23Na has a much smaller spin polarization than that of 87Rb because the population imbalances between the ground state Zeeman levels of 23Na are very small. The inefficient optical pumping can explain why Na magnetometers are not studied extensively. The investigation into the optical pumping process of 23Na is helpful in preparing a highly spin-polarized atomic medium and optimizing the sensitivity of Na magnetometers. [ABSTRACT FROM AUTHOR]

Time-dependent Ginzburg-Landau equations were solved by finite element method in two-dimensional space for order parameter and energy components of the annular superconducting sample in steady magnetic fields. Vortices preferred to penetrate from the inner surface of the annulus due to lesser energy required at the concave surface. A transition magnetic field strength was observed in spatial averages of carrier concentration and energy components, showing small bumps and abrupt variations, indicating phase transition from a non-vortex to vortex state. These effects were observed to repeat with every subsequent entry of a set of vortices into the sample; transition magnetic field strength was found to depend inversely on the annular width of the sample. The present work gives a better understanding of energy variations during phase transition from non-vortex to vortex state and predicts that vortex state can be avoided by tuning the wire thickness in practical applications, e.g., superconducting electromagnets. [ABSTRACT FROM AUTHOR]

Ferroelectric superlattice heterostructures have recently been explored for potential applications in electronic devices. In this letter, we employed the phase-field approach to simulate the domain structure and switching of a (BaTiO3)8/(SrTiO3)3 superlattice film constrained by a GdScO3 substrate. A constricted ferroelectric hysteresis loop was observed with a high saturation polarization but a small coercive field. The shape of the hysteresis loop is understood by analyzing the ferroelectric polarization distributions during switching. It is demonstrated that the multilayers stack behaves as dipole spring ferroelectric, named in analogy to exchange spring magnets in magnetic multilayers that show similar loops. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the magnetism and anomalous transport properties of the melt-spun ribbon Fe2MnAl alloy. It is found that the alloy exhibits ferromagnetic order with the Curie temperature of ∼150K, followed by another magnetic transition at T R ∼51K. It is suggested there is antiferromagnetism pinning effect on the ferromagnetic matrix at the temperature below T R . A steep rise of the resistance below T R has been observed, which can be understood in terms of antiferromagnetic scattering. An appearance of the resistance maximum near the Curie temperature and the negative temperature dependence of the resistance above Curie temperature are associated with the magnetic phase transition from ferromagnetism to paramagnetism. A negative magnetoresistance at low temperature arising from inhomogeneous magnetic scattering is reported. [ABSTRACT FROM AUTHOR]

Magnetically actuated functional gradient nanocomposites have widely been used for ultra-durable biomimetic interfaces and surfaces. However, the mechanical and thermal mismatches in integrated systems containing dissimilar materials or structures usually cause failures. By modulating the concentration of magnetic particles, a suitable mechanical gradient morphology can be generated to match different integrated systems. In this work, a new model is developed to describe magnetic particle motion under the magnetic field. Hybrid nano-reinforcements with two different magnetic particle sizes and concentrations were employed to optimize the magnetic particle concentration gradient. It was observed that the diversification of concentration distribution can be achieved by tuning the sizes and concentrations of nanoparticles. The present study, therefore, contributes toward the understanding of the transport mechanism of magnetic-field-actuated functional gradient nanocomposites and provides guidance for experiments to design ultra-durable biomimetic interfaces and surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Considering finite size effect, ferroelectric nanowires may show novel phenomena compared to ferroelectric thin film and bulk. Here we investigated the effect of width and surface compressive stress on electrocaloric cooling in ferroelectric nanowire by using thermodynamic calculations and phase‐field simulations. It was found that the isothermal entropy change and adiabatic temperature change in nanowire are 50% larger than that in thin film due to different mechanical boundary conditions of nanowire and thin film. The largest electrocaloric temperature changes were shown to increase significantly either with the decrease in nanowire width or the increase with the surface compressive stress. It was also revealed that the largest intrinsic entropy changes are almost the same for different nanowires with different widths and various stresses. The present study therefore contributes to the understanding of size effects of electrocaloric cooling and provides guidance for experiments to design high‐efficiency cooling devices using ferroelectric nanosystems. [ABSTRACT FROM AUTHOR]

In this paper, the effect of heat treatment on the structure and magnetic properties of the alloy is investigated by heat treating the melted Fe2Cr1-xMnxGa samples at different temperatures. It is found that the structure and magnetic properties of Fe2Cr1-xMnxGa are very sensitive to heat treatment and there is a certain degree of disorder. The structure of the prepared samples changes with different conditions of heat treatment, and the change in structure will in turn affect the magnetic behavior of the alloy. The magnetization intensity increases with increasing annealing temperature, indicating that the orderliness of the samples is improved by heat treatment. The magnetization intensity of the samples decreases with the doping of Mn content, which is due to the anti-parallel arrangement of the Fe-Mn spin magnetic moments by the doped Mn atoms. [ABSTRACT FROM AUTHOR]

We investigated stress-modulated magnetization precession frequency in Heusler-based spin transfer torque oscillator by combining micromagnetic simulations with phase field microelasticity theory, by encapsulating the magnetic tunnel junction into multilayers structures. We proposed a novel method of using an external stress to control the magnetization precession in spin torque oscillator instead of an external magnetic field. The stress-modulated magnetization precession frequency can be linearly modulated by externally applied uniaxial in-plane stress, with a tunable range 4.4–7.0 GHz under the stress of 10 MPa. By comparison, the out-of-plane stress imposes negligible influence on the precession frequency due to the large out-of-plane demagnetization field. The results offer new inspiration to the design of spin torque oscillator devices that simultaneously process high frequency, narrow output band, and tunable over a wide range of frequencies via external stress. [ABSTRACT FROM AUTHOR]

First-principles calculations were employed to investigate elastic and entropy properties of B 2 ferromagnetic and antiferromagnetic FeRh phases. We calculated lattice parameters, elastic constants, isotropic moduli like bulk modulus B , shear modulus G , Young’s modulus E , and Poisson’s ratio of two phases and compared these with other calculations and experiments. At finite temperatures, the values of vibrational (from both Debye model and phonon dispersion) and thermal electronic contributions to the total entropy change between the two phases are calculated about -50 J/kg/K and 7.8 J/kg/K comparable to the experimental results (−33 ± 9 J/kg/K and 8 ± 1 J/kg/K). [ABSTRACT FROM AUTHOR]

Fully compensated ferrimagnets do not create any magnetic stray field and allow for a completely polarized current of charges. As a result, these alloys show promising prospects for applications as spintronic devices. In this paper, we investigated the phase stability, the site preference, the tetragonal distortion and the influence of symmetry from the crystal structure and chemical environments of magnetic ions on the magnetic properties of Cr2YZ and Mn2YZ (Y = void, Ni, Cu, and Zn; Z = Ga, Ge, and As) full Heusler alloys by first-principles calculations. We found that the selected Cr2-based alloys, except for Cr2NiGa and Cr2NiGe, prefer to crystallize in the centrosymmetric L21-type structure, while the selected Mn2-based alloys, except for Mn2CuAs, Mn2ZnGe and Mn2ZnAs, tend to crystallize in the non-centrosymmetric XA-type structure. Due to the symmetry, the antiferromagnetism of the selected L21-type alloys is very stable, and no spin-polarized density of states could be generated. In contrast, the magnetic moment of the selected XA-type alloys depends heavily on the number of valence electrons and tetragonal distortion, and spin-polarized density of states is generated. Therefore, the selected alloys with L21-type structures and their tetragonal-distorted structure are potential candidates for conventional antiferromagnets, while those with XA-type structure and their tetragonal-distorted structure are promising candidates for (fully) compensated ferrimagnets. [ABSTRACT FROM AUTHOR]

Deformation-induced martensitic transformations (DIMTs) have been widely observed in iron and ferroalloys under various mechanical loading conditions, thereby showing extreme scientific merits and engineering significance. Since deformations and fractures affect one another and reflect the relative movements of atoms, DIMTs often accompany fractures. In this work, molecular dynamics simulation was performed with a (010) [100] pre-cracked model to study DIMTs from an α-Fe single crystal during the mode-I fracture process. The observed DIMTs were verified using first-principle calculations. A crack tip tracking algorithm by scanning the nearby atoms is proposed, and the obtained critical stress intensity factor was proved to be close to the experimental results. Quasi-cleavage fracture happened with the nucleation and growth of the γ (fcc) phase, which was transformed by activating the {121} 111 and {110} 111 shears near the crack tip. The layered ε (hcp) phase was formed by stacking faults inside the γ phase and was unstable by driving force analysis. [ABSTRACT FROM AUTHOR]

Twinning is a common phenomenon in crystal growth and mechanical deformation. It plays a key role in tuning the mechanical and transport properties of metals. In transition metal oxides, the twinning may give additional changes related to magnetism. Herein, the atomic configuration and the electronic structure of the twin boundaries (TBs) in rock‐salt‐type NiO are studied, combining aberration‐corrected transmission electron microscopy and first‐principles calculations. For NiO, the twinning occurs on the (111) plane, with oxygen atoms located at the TB and antiferromagnetic (AFM) coupling between the mirroring Ni atomic planes near the TB. The configuration gives the TB energy of 0.26 J m−2. Atomic and magnetic structures of fivefold twins in NiO are also investigated. In the structure of fivefold twins with the lowest energy, ferromagnetic coupling is formed in the AFM TBs due to the competing exchange interaction at the core of fivefold twins. [ABSTRACT FROM AUTHOR]

The local hydrogen distribution has significant influences on hydrogen embrittlement. In this work, mode-I fractures of (010)[100] pre-cracked α-Fe single crystal containing dissolved and absorbed hydrogen atoms are simulated by molecular dynamics and the time-stamped force-bias Monte Carlo methods. Statistics show that when located near the {112} plane, hydrogen atoms accelerate cleavage fracture and suppress the slip of {112}<111>; when located on the {110} plane, they promote martensite transformation and increase {110}<111> slip. Most adsorbed hydrogen atoms are concentrated near the inside of the crack surface and suppress fracture early by stress relaxation; therein concentrates stresses inside the matrix, and causes microvoid-coalescence fracture. • The hydrogen distribution and crack growth are linked by statistics. • Hydrogen promotes fracture by inhibiting {112}<111> slip in α-Fe. • The hydrogen on the {110} planes can enhance the martensitic transformation. • Adsorption of hydrogen can promote microvoid-coalescence fracture. • The voids in the matrix can be caused by hydrogen near the crack surface. [ABSTRACT FROM AUTHOR]

Magnetocaloric effects, because of their large entropy change, have been demonstrated to potentially revolutionize the solid-state cooling devices with high energy efficiency and environmental friendliness. However, the requirement of applying large magnetic fields obstructs the minimization of cooling devices. Here, we investigated electric-field-control magnetocaloric effects in magnetoelectric heterostructures by combining thermodynamic modelling and first-principle calculations. Based on strain-mediated mechanism, it is demonstrated that the interface strain of ferroelectric film under the electric field can tune the magnetic transition temperature from ferromagnetic to antiferromagnetic phases with 5 K shift under a small electric field of 0.1 MV/m and a giant entropy change of 14.9 J/(kg·K). In addition, we propose a potential multicaloric device including magnetocaloric and elastocaloric effects with high cooling efficiency based on magnetic-elastic-electric coupling phase transformations. The present study therefore contributes to the understanding of electric-field-control magnetocaloric cooling and provides guidance for experiments to design high efficiency and low-power consumption multicaloric cooling devices using magnetoelectric heterostructures. • The interface strain tunes the magnetic transition temperature. • We demonstrate the electric-field-control magnetocaloric effects. • We propose a potential multicaloric device with high cooling efficiency. [ABSTRACT FROM AUTHOR]

Nanosecond laser pulses from a 1064 nm Nd:YAG laser were focused on the atomized spray of RbCl aqueous solution whose threshold energy of plasma ignition is around 550 mJ in atmosphere. A narrow-linewidth (100 MHz) vertical-cavity surface-emitting laser (VCSEL) has been used to probe the transient density of ground-state atomic Rb. The frequency of VCSEL probe beam was locked to the 87Rb transition |52S1/2, F = 2 → |52P1/2, F′ = 1 which corresponds to an absorption cross-section of up to 10−10 cm2. The atomic Rb number density was inferred from the extinction ratio of transmitted light intensity. The simple mathematical model developed to describe the density evolution n(t) conforms with the detected increase-peak-decline-vanish process well. It is a sensitive and real-time method used to diagnose the evolution process of generated plasma in air. The detection limit of RbCl concentration is lower than 1 gram per litre. Rb atoms have a mean lifetime of 250 µs in each pulsed plasma. [ABSTRACT FROM AUTHOR]

Abstract Tetragonal Heusler alloys with high coercivity field (H C), low saturation magnetic moment and high Curie temperature (T C) have been considered as promising candidates for spin transfer torque (STT) applications. In this paper, tetragonal Heusler alloys Mn 3- x Cr x Ga have been designed and realized in experiments by adjusting the ratio of Mn/Cr and selecting suitable heat treatment conditions. It has been found that Mn 3- x Cr x Ga (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6 and 1) alloys exhibited multiple phase structures. As x > 0.5, both as-spun and as-annealed ribbons show pure B 2-type body-centered cubic (b.c.c.) structure. The D 0 22 -type tetragonal Heusler structure starts to appear in the matrix of cubic B 2 structure as x = 0.5 in as-annealed ribbon samples, and gradually develops to pure tetragonal structure as x = 0.3. There is a significant structure difference between as-annealed and as-spun ribbons as x ≤ 0.2. Cu 3 Au-type face-centered cubic (f.c.c.) structure is observed for as-spun ribbons, while the annealed ribbons show pure tetragonal structure. The pure tetragonal Heusler alloys have hard-ferrimagnetic properties with H c higher than 258 kA/m, accompanied by a high T C , large magnetic remanence (B r) and low magnetic moment at room temperature, which are important factors for spin-transfer torque applications. Our work reveals the tunability of the magnetic and structural properties of Heusler alloys by changing the ratio of doping elements, providing a guidance for further searching for tetragonal Heusler alloys. Highlights • Multiple pure phases of entire Mn 3- x Cr x Ga alloy series were obtained by distinct composition and heat treatment methods. • First-principles calculations of structural stability were used to interpret the experimental results. • Tetragonal Heusler alloys Mn 3- x Cr x Ga with potential application prospects were realized. [ABSTRACT FROM AUTHOR]

Exploration of magnetic 3 d element doped clathrate Eu 8 Ga 16 Ge 30 is an important field in clathrate studies. It covers complicated magnetic interactions among the moments of 3 d - and 4 f -atoms. In the current study, the Mn-doped sample with nominal composition of Eu 8 Ga 14 Mn 2 Ge 30 was prepared by the melt spinning technique. The incorporation of Mn into the lattice leads to a decrease in lattice parameters. Magnetization and modified Arrott plots indicate that the Mn-doped sample undergoes a second-order ferromagnetic-paramagnetic phase transition at ∼29.9 K, which is about 5 K lower than that of Mn-free Eu 8 Ga 16 Ge 30 ( T C  ∼ 34.7 K). The critical behavior around T C is investigated and critical values of β  = 0.35, γ  = 0.85, and δ  = 3.43 are calculated. In addition, a huge magnetic entropy change (-Δ S M ) improvement is observed due to Mn-doping. The sample shows a large − Δ S M max of ∼6.80 J/kg K around T C for a field change of 3 T. This is 17% higher than that of Mn-free Eu 8 Ga 16 Ge 30 . It is speculated that the substitution of Mn for Ga can introduce new 4 f -3 d exchange interactions that can lead to a more rapid magnetization process. The excellent magnetocaloric effect suggests the Mn-doped Eu 8 Ga 16 Ge 30 could be expected to have effective applications for low temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Si clathrates Ba 8− x Eu x Al 5 Si 41 with nominal x = 0, 0.1, 0.2, 0.3 and 0.4 have been synthesized by arc melting and acid washing so as to delete impure phases. Eu substitution for Ba in the clathrate results in introduction of magnetic moment and modification of crystalline structure. The decrease of the cubic lattice parameter a with the Eu content implies the incorporation of the Eu into the cages. The critical superconducting transition temperature T C decreases from 6.8 to 4.5 K as x increases from 0 to 0.3. For sample with nominal x = 0.4, no diamagnetic behavior indicative of superconductivity was found down to 2 K. These suggest that due to the introduction of the magnetic moment of Eu, the superconductivity was suppressed. In addition, the ferromagnetic interaction was also observed at the same time. For the Eu-free sample, both M - T and M - H curves show the typical behavior of type-II superconductivity. With the increases of Eu content, the superconducting lower critical field H C1 decreases and Weiss temperature increases. As x reaches to 0.4, superconductivity is totally suppressed and the sample shows only ferromagnetic behavior at low temperature. [ABSTRACT FROM AUTHOR]

Magnetic properties of Mn 50 Ni 40 In 10 − x Sb x alloys and thermal history effect on the magnetization behavior and magnetic entropy change of Mn 50 Ni 40 In 9 Sb 1 have been systematically studied. It indicates that the martensitic transformation temperature gradually increases with the increase of Sb content. Meanwhile, the overall magnetization of austenite decreases and that of martensite increases. The magnetization behavior, the critical magnetic field for martensite-to-austenite transformation and the magnetic entropy are very sensitive to the thermal history effect. The maximum magnetic entropy change is up to 27.1 J kg −1 K −1 in Mn 50 Ni 40 In 9 Sb 1 alloy under a magnetic field of 30 kOe with continuous heating method. [ABSTRACT FROM AUTHOR]

A phase-field model is developed to elucidate the process of polarization switching in BiFeO 3 thin film. The results demonstrated an energy-favorable mechanism for domain switching path and revealed possible ferroelectric domain switching modes. It is shown that 71° switching is dominant among the three possible switching paths, namely 71°, 109° and 180° switching. This might provide significant references for the application of ferroelectric materials under electric fields. [ABSTRACT FROM AUTHOR]

First-principles calculations have been used to study the structure stability, mechanical properties, dynamic stability, electronic structure, magnetic moment, and anomalous Hall conductivity of the quaternary Heusler alloy CoFeMnSn. It is found that the Type Ⅰ structure is the most energetically favorable configuration, which exhibits high mechanical and dynamic stability. The large experimental saturation magnetic moment of 4.16 μ B / f. u. and a high Curie temperature well above room temperature facilitate its application in the field of spintronics. The material's resistivity changes very little with increasing temperature, showing a weak negative temperature coefficient, indicating a non-metallic transport behavior of the alloy. The main carrier of the alloy is hole with a carrier concentration of roughly 2.49 × 1022 cm−3 at 300 K. The analysis of the anomalous transport properties of the alloy indicates that both intrinsic and extrinsic factors contribute to the anomalous Hall effect of the CoFeMnSn alloy. Although it is difficult to distinguish between the side-jump and intrinsic mechanisms, it is shown that the skew scattering associated with phonons plays a significant role in the anomalous Hall effect. • The magnetic, electronic structures and phonon dispersion curves are presented. • The anomalous Hall effect of alloys follows the extended scaling mechanism. • The phonon-dependent skewed scattering dominates the transport behavior of alloys. [ABSTRACT FROM AUTHOR]

There has been considerable interest in rare-earth doped silicon clathrate compounds in order to understand the relation between the 4 f electron moment and superconductivity. The Eu-doped silicon clathrates Ba 8− x Eu x Si 46 ( x =0, 0.5 and 1) were synthesized by using high-temperature and high-pressure. Structure characterization and magnetic measurement show Eu atoms enter clathrate lattice to occupy Ba positions. X-ray powder diffraction data indicate that the cubic lattice parameter a decreases with Eu doping. The magnetic measurements for all samples were studied. The incorporation of magnetic Eu 2+ into the lattice suppresses the superconductivity completely and induces the Curie-paramagnetic behavior at high temperature. The influences of Eu 2+ magnetic moment on the properties of samples were discussed. [ABSTRACT FROM AUTHOR]

Mn-based alloys have attracted considerable research interest in exploring new materials for the next generation of high-density and low-cost spintronic devices due to their variety of physical properties. The Ni 2 In-type Mn-based hexagonal alloys have been discovered for their potential application in martensitic phase transformation functional materials. However, the magnetotransport properties in these alloys have not been well studied. In this work, a comprehensive study including structure, magnetism and magnetotransport has been carried out on the Ni 2 In-type MnYSn (Y = Ti, Mn and Fe) alloys. The variation of saturation magnetization and Curie temperature in MnYSn alloys are analyzed. The anomalous Hall conductivity of MnTiSn and MnFeSn are dominated by the skew scattering mechanism, reaching 60 and 93 Ω−1 cm−1 at 5 K. The magnetotransport properties in MnYSn alloys suggest that it could be a potential candidate for magnetic sensors. • A pure Ni 2 In-type structure of MnYSn (Y = Ti, Mn and Fe) was obtained by melt-spun. • The variation of saturation magnetization and T C in MnYSn alloys are analyzed. • The transport properties of MnTiSn and MnFeSn are dominated by hole carriers. • The AHE in MnTiSn and MnFeSn is dominated by the skew scattering mechanism. [ABSTRACT FROM AUTHOR]

• The near SGS property of CoFeTiSn has been predicted by band structure. • Transport behavior indicates the alloy appear to have SGS like behavior. • The AHC of CoFeTiSn increases after annealing. • The effect of disorder on magnetic and transport properties have been studied. The magnetic and anomalous transport properties have been studied for the as-melted and annealed half-metallic ferromagnet CoFeTiSn. First-principles calculations suggest that CoFeTiSn presents band structure of the near spin-gapless semiconductor. The experiments show that the alloy's phase purity, chemical ordering and grain size have been improved by annealing, which causes a different transport property. The as-melted sample shows a temperature coefficient of resistivity sign transition from positive to negative accompanying the ferromagnetic–paramagnetic transition, while the annealed sample only shows negative temperature coefficient resistivity in the whole temperature range. The calculated positive ordinary Hall coefficient suggest that transport properties are dominated by the hole carrier. The measured saturation magnetic moment at 5 K is lower but close to 1 μ B / f. u , which is probably attributed to the inhomogeneous magnetic phase and the anti-site disorder between Co-Fe. The band structure of near spin-gapless semiconductor is another possible reason. The anomalous Hall conductivity changes from 20 S/cm to 27 S/cm after annealing due to the altered chemical ordering. The positive linear magnetoresistance indicates that the alloy appears to have spin-gapless semiconductor like behavior as predicted by its band structure. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the effects of Si addition and heat treatment on the martensitic transformation and magnetic properties of Ni43Mn46Sn11−x Si x (x = 1, 2, 3) alloys. The martensitic transformation temperatures were found to increase with increasing Si content in the alloy. A magnetic field-induced martensite-to-austenite transformation was found in Ni43Mn46Sn10Si1. Ageing of the Ni43Mn46Sn10Si1 alloy at 673 K resulted in the formation of a (Mn,Ni)–SiSn precipitate. The precipitate contains very low Sn content, causing the increase of the Sn content in the matrix phase and a decrease of martensitic transformation temperature. Ageing at 573 K is found to increase the Curie temperature and the saturation magnetization. This is attributed to the increase of atomic ordering of the matrix. Solution treatment of the aged samples at 1073 K was effective to restore the original transformation behaviour and magnetic properties. [Copyright &y& Elsevier]

Abstract: Geometrical frustration, which arises from the topology of a well-ordered structure rather than from disorder, has recently become a renewed interest. In particular, geometrical frustration among spins in the spinel oxides can lead to exotic low-temperature states. We reported a joint experimental and theoretical investigation of Fe-doping effect on LiMn2O4 spinel oxide in which magnetic moments have geometrical frustration. The structural and physical properties of LiMn1.5Fe0.5O4 were studied by means of Mossbauer spectroscopy, X-ray diffraction, scanning electron microscope (SEM), electrical and magnetic measurements. Electronic conductivity measurements showed that Verwey-type transition is absent in heavily Fe-doped LiMn2O4. In addition, LiMn1.5Fe0.5O4 exhibits a semiconductor characteristic in resistivity with an energy gap E g =0.27eV, which is consistent with our first-principle simulation. A large resistivity at room temperature for LiMn1.5Fe0.5O4 indicates low concentration of conduction electrons corresponding to electronic localization behavior. X-ray diffraction refinement as well as Mossbauer analysis suggests that Fe ions preferentially substitute for Mn ions on the octahedral B-sites. Moreover, small amount of Fe replace for Li ions to form a site inversion in spinel structure. In contrast to the pure and low-Fe-doped LiMn2O4 samples, LiMn1.5Fe0.5O4 has an antiferromagnetic transition at T N =34K. The Fe dopants enhance the antiferromagnetic interaction among moments accompanied by breaking the original moment equilibrium and suppressing the magnetic frustration in LiMn2O4. [Copyright &y& Elsevier]

• Co doping partial Ga in Ga 2 MnNi introduces AFM in FM matrix. • Both T C and M S decrease first and then increase with increasing Co in Ga 2−x MnNiCo x. • Re-entrant spin glass transition has been observed in Ga 1.5 MnNiCo 0.5. The influence of Co on the crystal structure and magnetic properties of the Ga 2−x MnNiCo x (x = 0,0.3,0.5,0.7) are investigated in this study. It has been found that the doping of Co does not change the cubic Heusler structure of the parent compound Ga 2 MnNi. The introduction of a small amount of Co reduces the p-d covalent hybridization effect and decreases the degree of atomic ordering, resulting in an abnormal increase in the lattice parameter when x = 0.3 (from 5.8387 ± 0.0020 Å to 5.8665 ± 0.0012 Å). The atomic size effect plays the main role when x > 0.3, leading to the decrease of lattice parameter. Due to the influence of the lattice parameter and the atomic site occupation on the magnetic interaction, the Curie temperature (T C) and the saturation magnetization are found to decrease at first and then increase with the chemical substitution of Co for Ga. A reentrant spin glass (RSG) below T f = 65.8 K is confirmed in Ga 1.5 MnNiCo 0.5 alloy due to the competition of ferromagnetic and antiferromagnetic interactions. [ABSTRACT FROM AUTHOR]

• A new type of metastable structure on the (1 1 1) surface of ceria nanoparticles is induced by electron beam. • The Ce-termination surface has been identified close to surface steps. • The Ce-terminated surface have the outermost and subsurface Ce atoms reduced from Ce4+ to Ce1+ and Ce3+, respectively. • The highly reduced O-termination surface at steps were observed. Applications of ceria (CeO 2) in catalysis are closely related to the behavior of oxygen at the surface and subsurface. In this study, we show that the steps at the (1 1 1) surface of CeO 2 are highly reducible. Using aberration-corrected transmission electron microscopy, we observed simultaneous loss of surface and subsurface oxygen close to a step. Despite their large changes in atomic coordination, the outermost Ce atoms in the Ce-terminated surface has a negligible relaxation compared with the O-terminated surface. The outermost and subsurface Ce atoms of the Ce-terminated surface are reduced to valences of +1 and +3, and electronic configuration of 5 s 25 p 64 f 16 s 2 and 5 s 25 p 64 f 1, respectively. Both of them have a local magnetic moment and they couple antiferromagnetically. The existence of the Ce-termination is important for a complete understanding of the surface structure and properties of CeO 2. [ABSTRACT FROM AUTHOR]

• The ground state of cubic Ti 2 CoGa is L2 1 structure without tetragonal distortion. • Replacing Co with Ni can stimulate the tetragonal distortion of Ti 2 CoGa alloy. • Tetragonal distortion is expected in Ti 2−x M x CoGa (M = V, Cr, Fe) system alloys. In this work, the structure and potential tetragonal distortion (TD) properties of Ti 2 CoGa and its M−doped (M = V, Cr, Mn, Fe, Ni) system are studied in detail by first-principles calculations. The result shows that Ti 2 CoGa alloy should crystalize in cubic L2 1 -type structure and no tetragonal distortion is discovered, which limits its application. Attempts are made to seek new tetragonal Heusler materials by replacing Ti or Co atoms in Ti 2 CoGa with element M (M = V, Cr, Mn, Fe, Ni). It is found that all the Ti 2 Co 1−x M x Ga (x = 0.25, 0.5, 0.75; M = V, Cr, Mn, Fe, Ni) compounds tend to form L2 1 structure, and only Ti 2 Co 1−x Ni x Ga has the possibility of TD when x > 0.29. For Ti 2−x M x CoGa (x = 0.25, 0.5, 0.75) system, the increase of the doping amount results in the cubic ground state of the alloy turning from L2 1 to XA structure. Furthermore, energy curves with different structures show that the tendency of TD in the alloy can be excited after substitution V (x = 0.29–0.50), Cr (x = 0.31–0.43) and Fe (x = 0.21–0.29) for partial Ti. This research can inspire us to search and realize new tetragonal Heusler materials by suitable doping in ternary Heusler alloys. [ABSTRACT FROM AUTHOR]

• Reveal a counterexample of site preference rule for Heusler alloys. • Predict half-metallicity in Vanadium-based alloys. • Confirm two different Slater-Pauling curves for XA -type configuration. We reported a new atomic site preference occupation for Vanadium-based X 2 YZ full Heusler alloys. It tells that alloys with less 24 valence electrons form the L 2 1 -type structure, while others form the XA -type structure. This fact means that the site preference rule for Vanadium-based alloys depends on the total number of valence electrons instead of the electropositive between X and Y atoms. The magnetic moments of XA -type alloys follow the Slater-Pauling rules, with two forms, M t = N V − 24 and M t = N V − 18 corresponding to different origins of the band gaps. XA -type V 2 YZ (Y = Cr, Mn and Fe; Z = Ga, Ge and As), V 2 CoGa, V 2 CoGe and V 2 NiGa alloys have half-metallic property. L 2 1 - type V 2 YZ (Y = Cu and Zn; Z = Ga, Ge and As) alloys show no spin polarization and no half-metallic property due to the structural symmetry and the non-magnetism of copper and zinc atoms. [ABSTRACT FROM AUTHOR]

The crystal structure, magnetic and electronic properties and influence of order on half-metallicity of a quaternary Heusler CoFeTiSn alloy were studied. We found that CoFeTiSn alloy crystallizes to a LiMgPdSn prototype structure (space group F- 43 m , No. 216). The relationship between the magnetic moments (M t = 1 μ B) and the number of valence electrons (N V = 25) obeys the Slater-Pauling rule M t = N V - 24. The electronic structure shows half-metallic property. Anti-site disorder between magnetic atoms Fe (or Co) and non-magnetic atoms Ti (or Sn), i.e. Co 1- x Ti x , Co 1- x Sn x , Fe 1- x Ti x and Fe 1- x Sn x has a significant influence on the magnetic and electronic properties of the alloys and is harmful to the half-metallic property. Anti-site disorder could be effectively depressed under ordering treatment. These results indicate CoFeTiSn is a potential half-metallic ferromagnet and promising for spintronic applications. • Confirm the LiMgPdSn structure and atomic arrangement of CoFeTiSn. • Predict the half-metallicity for CoFeTiSn. • Reveal the influence of anti-site disorder on half-metallicity. [ABSTRACT FROM AUTHOR]