Search

Interaction between dipoles often emerges intriguing physical phenomena, such as exchange bias in the magnetic heterostructures and magnetoelectric effect in multiferroics, which lead to advances in multifunctional heterostructures. However, the defect-dipole tends to be considered the undesired to deteriorate the electronic functionality. Here, we report deterministic switching between the ferroelectric and the pinched states by exploiting a new substrate of cubic perovskite, BaZrO$_{3}$, which boosts square-tensile-strain to BaTiO$_{3}$ and promotes four-variants in-plane spontaneous polarization with oxygen vacancy creation. First-principles calculations propose a complex of an oxygen vacancy and two Ti$^{3+}$ ions coins a charge-neutral defect-dipole. Cooperative control of the defect-dipole and the spontaneous polarization reveals ternary in-plane polar states characterized by biased/pinched hysteresis loops. Furthermore, we experimentally demonstrate that three electrically controlled polar-ordering states lead to switchable and non-volatile dielectric states for application of non-destructive electro-dielectric memory. This discovery opens a new route to develop functional materials via manipulating defect-dipoles and offers a novel platform to advance heteroepitaxy beyond the prevalent perovskite substrates., According to the Copyright Policy, the submission version (before peer-review and revision)

Spinel oxides are versatile and functional materials with physicochemical properties that are significantly influenced by their structural disorder. The transition from layered double hydroxides (LDHs) to mixed metal oxides (MMOs) containing spinel oxides is a powerful approach to create materials with tailored properties suitable for various applications. Herein, we report the control of structural ordering in spinels related to the crystallinity, cationic inversion, and coordination number of constituent atoms by varying the transformation energy. Transformation from LDHs to spinels with higher applied energy leads to higher crystallinity, lower degree of inversion, and lower ratios of low-coordinated atoms to fully coordinated atoms after treatment with acid. We provide a general framework for controlling structural ordering, that can be applied to other spinels and metal oxides. In addition, LDHs and MMOs possess many chemical and structural degrees of freedom, making it possible to create materials that suit the needs of different applications, such as memory, sensors, catalysis, and energy conversion.

Nitrogen ion implantation is a useful technique to put nitrogen ions into lattices. In this work, nitrogen ion implantation into epitaxial Mo films is performed to create a buried superconducting γ-Mo2N. Atomically flat epitaxial (110) Mo films are grown on (0001) Al2O3. By impinging nitrogen ions, where the beam energy is fixed to 20 keV, we observe (111) γ-Mo2N diffraction and the formation of a γ-Mo2N layer from X-ray reflectivity. Magnetization and transport measurements clearly support a superconducting layer in the implanted film. Our strategy shows that formation of a buried superconducting layer can be achieved through ion implantation and self-annealing.

We demonstrate the effect of the crystallinity of ceramic targets on the electronic properties of LaNiO3 (001) thin films epitaxially grown by pulsed laser deposition (PLD). We prepared two kinds of LaNiO3 targets with different crystallinity by manipulating calcination temperature (i.e., 300 and 1000 °C) in the solid state reaction for ceramic synthesis. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS) experiments of the as-sintered LaNiO3 ceramic targets clearly show that the LaNiO3 target sintered after high-temperature (1000 °C, high crystallinity) calcination is more oxidized to Ni3+ with better crystallinity than the LaNiO3 target sintered after low-temperature (300 °C, poor crystallinity) calcination. Using these two LaNiO3 ceramics as PLD targets, we fabricated epitaxial LaNiO3/LaAlO3 (001) thin-film heterostructures to examine how target crystallinity affects the physical properties of LaNiO3 films. Intriguingly, the electri...

To create an environment for IoT devices, securely, it is necessary to establish a cryptographic key for those devices. Conventionally, this key has been stored on the actual device, but this leaves the key vulnerable to physical attacks in the IoT environment. To solve this problem, several research studies have been conducted on how best to conceal the cryptographic key. Recently, these studies have most often focused on generating the key dynamically from noisy data using a fuzzy extractor or providing secure storage using a fuzzy commitment. Thus, far, all of these studies use only one type of noisy source data, such as biometric data or physical unclonable function (PUF). However, since most IoT devices are operated in unmanned environments, where biometric data is unavailable, the method using biometric data cannot be utilized for unmanned IoT devices. Although the method using PUF is applied to these unmanned devices, these are still vulnerable against physical attacks including unintended move or theft. In this paper, we present a novel way to use the fuzzy commitment on such devices, called two-factor fuzzy commitment scheme. The proposed method utilizes two noisy factors from the inside and outside of the IoT device. Therefore, although an attacker acquiring the IoT device can access the internal noisy source, the attacker cannot extract the right key from that information only. We also give a prototype implementation for ensuring the feasibility of our two-factor fuzzy commitment concept by utilizing the image data and PUF data for two noisy factors.

We comprehensively investigated the magnetic, ferroelectric, and ME properties of ${\mathrm{Ba}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Co}}_{2}{({\mathrm{Fe}}_{1\ensuremath{-}y}{\mathrm{Al}}_{y})}_{12}{\mathrm{O}}_{22}$ single crystals in broad doping ranges of Sr $(1.0\ensuremath{\le}x\ensuremath{\le}1.8)$ and Al $(0.00\ensuremath{\le}y\ensuremath{\le}0.08)$. Most of the investigated compounds exhibit an intriguing coexistence of two apparently competing magnetic phases: a transverse conical (TC) and alternating longitudinal conical (ALC) spin structure. The magnetic properties show that the ${\mathrm{Ba}}_{0.2}{\mathrm{Sr}}_{1.8}{\mathrm{Co}}_{2}{({\mathrm{Fe}}_{0.96}{\mathrm{Al}}_{0.04})}_{12}{\mathrm{O}}_{22}$ crystal has the highest ordering temperature and largest volume fraction of the ALC phase at zero H; further, after the application of an in-plane H, it exhibits a maximized volume fraction of the metastable TC phase, resulting in the highest ME susceptibility and electric polarization at all temperatures below 300 K. Our findings demonstrate that securing the thermal stability of the ALC phase is a crucial prerequisite to achieve optimized ME coupling in ${\mathrm{Co}}_{2}\mathrm{Y}$-type hexaferrites, pointing to a general strategy applicable to other hexaferrites as well.

Nitrogen ion implantation is a useful technique to put nitrogen ions into lattices. In this work, nitrogen ion implantation into epitaxial Mo films is performed to create a buried superconducting γ-Mo

Enhanced and self-biased magnetoelectric (ME) coupling is demonstrated in a laminate heterostructure comprising 4 μm-thick Pb(Zr,Ti)O3 (PZT) film deposited on 50 μm-thick flexible nickel (Ni) foil. A unique fabrication approach, combining room temperature deposition of PZT film by granule spray in vacuum (GSV) process and localized thermal treatment of the film by laser radiation, is utilized. This approach addresses the challenges in integrating ceramic films on metal substrates, which is often limited by the interfacial chemical reactions occurring at high processing temperatures. Laser-induced crystallinity improvement in the PZT thick film led to enhanced dielectric, ferroelectric, and magnetoelectric properties of the PZT/Ni composite. A high self-biased ME response on the order of 3.15 V/cm·Oe was obtained from the laser-annealed PZT/Ni film heterostructure. This value corresponds to a ∼2000% increment from the ME response (0.16 V/cm·Oe) measured from the as-deposited PZT/Ni sample. This result is also one of the highest reported values among similar ME composite systems. The tunability of self-biased ME coupling in PZT/Ni composite has been found to be related to the demagnetization field in Ni, strain mismatch between PZT and Ni, and flexural moment of the laminate structure. The phase-field model provides quantitative insight into these factors and illustrates their contributions toward the observed self-biased ME response. The results present a viable pathway toward designing and integrating ME components for a new generation of miniaturized tunable electronic devices.

Here we report a quasi-one-dimensional $S=1$ chain compound ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$. From the comprehensive study of the structure and magnetic properties on high-quality single-crystalline ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$, it is revealed that ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$ undergoes a transition into an intriguing long-range antiferromagnetic order at ${T}_{\mathrm{N}}=30.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, in which longitudinal magnetic moments along the chain direction are ferromagnetically ordered, while their transverse components have an alternating ferromagnetic-antiferromagnetic coupling. Even though the temperature dependence of magnetic susceptibility represents an archetypal anisotropic antiferromagnetic order, we found that critical behavior of unconventional nature with ${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\sim}0.25$ and $\ensuremath{\beta}\ensuremath{\sim}0.18$ is accompanied by the temperature evolution of the antiferromagnetic order parameter.

Ferroelectricity occurs in crystals with broken spatial inversion symmetry. In conventional perovskite oxides, concerted ionic displacements within a three-dimensional network of transition metal-oxygen polyhedra (MOx) manifest spontaneous polarization. Meanwhile, some two-dimensional networks of MOx can foster geometric ferroelectricity with magnetism, owing to the distortion of the polyhedra. Because of the fundamentally different mechanism of ferroelectricity in a two-dimensional network, one can further challenge an uncharted mechanism of ferroelectricity in a one-dimensional channel of MOx and estimate its feasibility. This communication presents ferroelectricity and coupled ferromagnetism in a one-dimensional FeO4 tetrahedral chain network of a brownmillerite SrFeO2.5 epitaxial thin film. The result provides a new paradigm for designing low-dimensional MOx networks, which is expected to benefit the realization of macroscopic ferro-ordering materials including ferroelectric ferromagnets., 28 pages, 1 table, 3 figures, 5 supplementary figures

We investigate thermal fluctuations in terms of diamagnetism and magnetotransport in superconducting NaFe1−xCoxAs single crystals with different doping levels. Results show that in the case of optimal doped and lightly overdoped (x = 0.03, 0.05) crystals the analysis in the critical as well as in the Gaussian fluctuation regions is consistent with the Ginzburg-Landau 3D fluctuation theory. However, in the case of strongly overdoped samples (x ≥ 0.07) the Ullah-Dorsey scaling of the fluctuation induced magnetoconductivity in the critical region confirms that thermal fluctuations exhibit a 3D anisotropic nature only in a narrow temperature region around Tc(H). This is consistent with the fact that in these samples the fluctuation effects in the Gaussian region above Tc may be described by the Lawrence-Doniach approach. Our results indicate that the anisotropy of these materials increases significantly with the doping level.

We studied a low-field giant magnetostrictive spin-flop transition in a colossal magnetoresistance manganite ${\mathrm{La}}_{1.4}{\mathrm{Sr}}_{1.6}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ using resonant soft x-ray diffraction and soft x-ray absorption spectroscopy at the Mn ${L}_{2,3}$ edge. The spin-flop transition is induced by an instability of magnetocrystalline anisotropy near a critical ${e}_{g}$ orbital configuration with a balanced occupation in ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ states, which contribute in-plane and out-of-plane orbital angular momenta, respectively. The magnetic field drives a certain change in the orbital occupation with lattice distortion to switch the magnetic anisotropy, resulting in the spin-flop transition. These results provide a comprehensive mechanism of interplay between spin, orbital, and lattice degrees of freedom to realize a low-field giant magnetoelasticity.

Isotopic compositions of precipitation have been used to understand moisture transport in the atmosphere and interactions between precipitation and groundwater. Isotopic compositions of speleothems and ice cores, so called, ‘‘paleoarchives’’, can be utilized to interpret climate of the past and global circulation models (GCMs). The GCMs are able to explain the paleoarchives, can be validated by the precipitation isotopes. The developments of stable isotope analyzers make high-resolution isotopic studies feasible. Therefore, a high-resolution study of precipitation isotopes is needed. For this study, precipitation samples were collected for every 5 to 15 minutes, depending on precipitation rates, using an auto-sampler for precipitation isotopes near coastal area. The isotopic compositions of precipitation range from -5.7‰ (-40.1‰) to -10.8‰ (-74.3‰) for oxygen (hydrogen). The slope of δ 18 O-δD diagram for the whole period is 6.8, but that of each storm is 5.1, 4.2, 7.9 and 7.7, respectively. It indicates that evaporation occurred during the first two storms, while the latter two storm did not experience any evaporation. The isotopic fractionations of precipitation has significant implications for the water cycle and high-resolution data of precipitation isotopes will be needed for the future studies.

We report extraordinarily large magnetic hysteresis loops in the iridates ${\mathrm{Sr}}_{3}{\mathrm{NiIrO}}_{5}$ and ${\mathrm{Sr}}_{3}{\mathrm{CoIrO}}_{6}$. We find coercive magnetic fields of up to 55 T with switched magnetic moments $\ensuremath{\approx}1\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ per formula unit in ${\mathrm{Sr}}_{3}{\mathrm{NiIrO}}_{6}$ and coercive fields of up to 52 T with switched moments $\ensuremath{\approx}3\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ per formula unit in ${\mathrm{Sr}}_{3}{\mathrm{CoIrO}}_{6}$. We propose that the magnetic hysteresis involves the field-induced evolution of quasi-one-dimensional chains in a frustrated triangular configuration. The striking magnetic behavior is likely to be linked to the unusual spin-orbit-entangled local state of the ${\mathrm{Ir}}^{4+}$ ion and its potential for anisotropic exchange interactions.

We present the results of the high-temperature neutron and x-ray diffraction experiments on the Ca3-xSrxTi2O7 (x = 0.5, 0.8, 0.85, 0.9) compounds. The ferro- to paraelectric transition in these hybrid improper ferroelectric materials arises from the so-called trilinear coupling. Depending on the Strontium content, various structures and phase transitions, different from theoretical predictions, emerge. The in-situ x-ray powder diffraction indicates a direct ferro- to paraelectric transition between the orthorhombic A21am and tetragonal undistorted I4/mmm phase for x < 0.6. We identified a reduction in the trilinear coupling robustness by increasing the Sr-doping level to lead to the emergence of the intermediate tetragonal P42/mnm phase and the gradual suppression of the orthorhombic phase. The observed character of the structure transitions and the Ca3-xSrxTi2O7 phase diagram are discussed in the framework of theoretical models of other related hybrid improper ferroelectric systems., 10 pages, 3 figures, 1 table

Field-induced switching of ferroelectric domains with a topological vortex configuration is studied by atomic imaging and electrical biasing in an electron microscope, revealing the role of topological defects on the topologically-guided change of domain-wall pairs in a hexagonal manganite.

We combined high field optical spectroscopy and first principles calculations to analyze the electronic structure of ${\mathrm{Ni}}_{3}{\mathrm{TeO}}_{6}$ across the 53 K and 9 T magnetic transitions, both of which are accompanied by large changes in electric polarization. The color properties are sensitive to magnetic order due to field-induced changes in the crystal field environment, with those around Ni1 and Ni2 most affected. These findings advance the understanding of magnetoelectric coupling in materials in which magnetic $3d$ centers coexist with nonmagnetic heavy chalcogenide cations.

We investigate the Hall coefficient R H , resistivity, and magnetization of URu 2 Si 2 and U ( Ru 0.96 Rh 0.04 ) 2 Si 2 in the high field regime up to 45 T to trace the electronic structure changes in both high and low temperature regimes. We find that at high temperatures above ∽ 7 K , temperature- and field-dependent positions of R H maxima and magnetoresistance maxima coincide with a coherent temperature T coh at each field. These systematically decrease in temperatures with increasing fields and extrapolate to zero at the field-induced putative quantum critical point (QCP). This observation suggests a collapse of a new energy scale, i.e., a coherent temperature of a heavy quasiparticle band, at the putative field-induced QCP. At lower temperatures, we show there are discontinuous changes of the Hall number n H = 1 / R H e at the phase boundaries. This behavior illustrates that the phase formation is caused by first order reconstructions of the Fermi surface, which we interpret to the polarization of Fermi surface pockets seen in de-Haas van-Alphen (dHvA) measurements.

We report the specific heat measurement of a YCrO3 single crystal in a wide temperature range from 30 to 360 K by use of a newly designed microcalorimeter with high sensitivity about ∼1J/K. The measured heat capacity data exhibit a -like shape at the N´ eel temperature TN ≈ 140 K as consistent with the second order magnetic transition. When the phonon specific heat is subtracted by use of that of a non-magnetic analogue LaGaO3 with an orthorhombic structure, the remaining entropy is much higher than the expected magnetic entropy from Cr 3+ (S = 3/2) ions. We attribute the excess entropy to the additional phonon entropy caused by the monoclinic structure of YCrO3, which can be intimately related to its ferroelectric property. © 2006 Elsevier B.V. All rights reserved.

We combined high field optical spectroscopy and first principles calculations to analyze the electronic structure of Ni_{3}TeO_{6} across the 53 K and 9 T magnetic transitions, both of which are accompanied by large changes in electric polarization. The color properties are sensitive to magnetic order due to field-induced changes in the crystal field environment, with those around Ni1 and Ni2 most affected. These findings advance the understanding of magnetoelectric coupling in materials in which magnetic 3d centers coexist with nonmagnetic heavy chalcogenide cations.

We report the discovery of a metamagnetic phase transition in a polar antiferromagnet Ni_{3}TeO_{6} that occurs at 52 T. The new phase transition accompanies a colossal magnetoelectric effect, with a magnetic-field-induced polarization change of 0.3 μC/cm^{2}, a value that is 4 times larger than for the spin-flop transition at 9 T in the same material, and also comparable to the largest magnetically induced polarization changes observed to date. Via density-functional calculations we construct a full microscopic model that describes the data. We model the spin structures in all fields and clarify the physics behind the 52 T transition. The high-field transition involves a competition between multiple different exchange interactions which drives the polarization change through the exchange-striction mechanism. The resultant spin structure is rather counterintuitive and complex, thus providing new insights on design principles for materials with strong magnetoelectric coupling.

The hexagonal phase of $\mathrm{LuFe}{\mathrm{O}}_{3}$ is a rare example of a multiferroic material possessing a weak ferromagnetic moment, which is predicted to be switchable by an electric field. We stabilize this structure in bulk form though Mn and Sc doping, and determine the complete magnetic and crystallographic structures using neutron-scattering and magnetometry techniques. The ferroelectric $P{6}_{3}cm$ space group is found to be stable over a wide concentration range, ordering antiferromagnetically with N\'eel temperatures that smoothly increase following the ratio of $c$ to $a\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}(c/a)$ lattice parameters up to 172 K, the highest found in this class of materials to date. The magnetic structure for a range of temperatures and dopings is consistent with recent studies of high quality epitaxial films of pure hexagonal $\mathrm{LuFe}{\mathrm{O}}_{3}$ including a ferromagnetic moment parallel to the ferroelectric axis. We propose a mechanism by which room-temperature multiferroicity could be achieved in this class of materials.

Layered $5d$ transition metal dichalcogenide (TMD) $\mathrm{IrT}{\mathrm{e}}_{2}$ is distinguished from the traditional TMDs (such as $\mathrm{NbS}{\mathrm{e}}_{2})$ by the existence of multiple charge-density wave (CDW)-like stripe phases and superconductivity at low temperatures. Despite intensive studies, there is still no consensus on the physical origin of the stripe phases or even the ground state modulation for this $5d$ material. Here we present atomic-scale evidence from scanning tunneling microscopy and spectroscopy (STM/STS) that the ground state of $\mathrm{IrT}{\mathrm{e}}_{2}$ is a $q=1/6$ stripe phase, identical to that of the Se-doped compound. Furthermore, our data suggest that the multiple transitions and stripe phases are driven by the intralayer Ir-Ir dimerization that competes against the interlayer Te-Te bonding. The competition results in a unified phase diagram with a series of hierarchical modulated stripe phases, strikingly similar to the renowned ``devil's staircase'' phenomena.

Common mathematical theories can have profound applications in understanding real materials. The intrinsic connection between aperiodic orders observed in the Fibonacci sequence, Penrose tiling, and quasicrystals is a well-known example. Another example is the self-similarity in fractals and dendrites. From transmission electron microscopy experiments, we found that FexTaS2 crystals with x = 1/4 and 1/3 exhibit complicated antiphase and chiral domain structures related to ordering of intercalated Fe ions with 2a × 2a and √3a × √3a superstructures, respectively. These complex domain patterns are found to be deeply related with the four color theorem, stating that four colors are sufficient to identify the countries on a planar map with proper coloring and its variations for two-step proper coloring. Furthermore, the domain topology is closely relevant to their magnetic properties. Our discovery unveils the importance of understanding the global topology of domain configurations in functional materials.

Standing on successful first principles predictions for new functional ferroelectric materials, a number of new ferroelectrics have been experimentally discovered. Utilizing trilinear coupling of two types of octahedron rotations, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the Ruddlesden-Popper compounds (Ca$_{3}$Ti$_{2}$O$_{7}$, Ca$_{3}$Mn$_{2}$O$_{7}$, and (Ca/Sr/Ba)$_{3}$(Sn/Zr/Ge)$_{2}$O$_{7}$). However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. Here we provide the first experimental demonstration of room-temperature switchable polarization in the bulk crystals of Ca$_{3}$Ti$_{2}$O$_{7}$ as well as Sr-doped Ca$_{3}$Ti$_{2}$O$_{7}$. In addition, (Ca,Sr)$_{3}$Ti$_{2}$O$_{7}$ is found to exhibit an intriguing ferroelectric domain structure resulting from orthorhombic twins and (switchable) planar polarization. The planar domain structure accompanies abundant charged domain walls with conducting head-to-head and insulating tail-to-tail configurations, which exhibit two-order-of-magnitude conduction difference. These discoveries provide new research opportunities not only on new stable ferroelectrics of Ruddlesden-Popper compounds, but also on meandering conducting domain walls formed by planar polarization.

We study magnetic and multiferroic behavior in Ca${}_{3}$Co${}_{2\ensuremath{-}x}$Mn${}_{x}$O${}_{6}$ ($x\ensuremath{\sim}$ 0.97) by high-field measurements of magnetization ($M$), magnetostriction [$L$($H$)/$L$], electric polarization ($P$), and magnetocaloric effect. This study also gives insight into the zero- and low-magnetic-field magnetic structure and magnetoelectric coupling mechanisms. We measured $M$ and $\ensuremath{\Delta}$$L$/$L$ up to pulsed magnetic fields of 92 T, and determined the saturation moment and field. On the controversial topic of the spin states of Co${}^{2+}$ and Mn${}^{4+}$ ions, we find evidence for $S=\frac{3}{2}$ spins for both ions with no magnetic-field-induced spin-state crossovers. Our data also indicate that Mn${}^{4+}$ spins are quasi-isotropic and develop components in the $ab$ plane in applied magnetic fields of 10 T. These spins cant until saturation at 85 T, whereas the Ising Co${}^{2+}$ spins saturate by 25 T. Furthermore, our results imply that the mechanism for suppression of electric polarization with magnetic fields near 10 T is flopping of the Mn${}^{4+}$ spins into the $ab$ plane, indicating that appropriate models must include the coexistence of Ising and quasi-isotropic spins.

Benzotriazol-1-yl alkyl carbonate 1 has been found to be a new convenient and inexpensive coupling agent to prepare an active ester 2 for the synthesis of an amide 3 in good yield and with high purity.

In the core of quantum Hall effect, intrinsic anomalous Hall effect (AHE), and intrinsic spin Hall effect lies the Berry phase, a quantum mechanical phase associated with an adiabatic change of the system. However, experimental evidences supporting this new recognition are scarce in three-dimensional systems. We report here that the anomalous Hall conductivity of metallic GaMnAs samples, when properly scaled by the carrier concentration, remains constant regardless of the ferromagnetic transition temperature from 50 to 160 K. In addition, the constant agrees with the theoretical prediction quite well. These qualitative and quantitative agreements support the idea of intrinsic AHE originated from momentum-space Berry phase firmly. Furthermore, the tunability of intrinsic AHE in the diluted magnetic semiconductors can be utilized in the semiconductor spintronics applications.

Comparative study of U ( Ru 1 - x Rh x ) 2 Si 2 ( x = 0 and 4%) through resistivity, magnetic susceptibility, and Hall coefficient measurements reveals that the coherence temperature, T coh , of the Rh 4% doped sample clearly decreases by about 10–20% as compared with that of undoped one located around 50 K. Furthermore, T * , a characteristic temperature below which the resistivity shows the T 2 dependence, is also found to decrease by almost the same factor. These findings suggest that the low Rh doping sensitively destroys the itinerant band gap due to the hidden order (HO) through the reduction of the Fermi surface volume in the quasi-particle band.

The manipulation of magnetic ordering with applied electric fields is of pressing interest for new magnetoelectric devices and information storage applications. Recently, such magnetoelectric control was realized in multiferroics. However, their magnetoelectric switching is often accompanied by significant hysteresis, resulting from a large barrier, separating different ferroic states. Hysteresis prevents robust switching, unless the applied field overcomes a certain value (coercive field). Here we address the role of a switching barrier on magnetoelectric control, and identify a material, collinear antiferromagnetic and pyroelectric Ni3TeO6, in which magnetoelectric switching occurs without hysteresis. The barrier between two magnetic states in the vicinity of a spin–flop transition is almost flat, and thus small changes in external electric/magnetic fields allow to switch the ferroic state through an intermediate state in a continuous manner, resulting in a colossal magnetoelectric response. This colossal magnetoelectric effect resembles the large piezoelectric effect at the morphotropic phase boundary in ferroelectrics. Usually magnetoelectric switching is accompanied by hysteresis, which is a consequence of the large barrier between different magnetoelectric states. Here, the authors show that in the antiferromagnet Ni3TeO6magnetoelectric switching of magnetization as well as polarization occur without hysteresis.

Structural and magnetic chiralities are found to coexist in a small group of materials in which they produce intriguing phenomenologies such as the recently discovered Skyrmion phases. Here, we describe a previously unknown manifestation of this interplay in ${\mathrm{MnSb}}_{2}{\mathrm{O}}_{6}$, a trigonal oxide with a chiral crystal structure. Unlike all other known cases, the ${\mathrm{MnSb}}_{2}{\mathrm{O}}_{6}$ magnetic structure is based on corotating cycloids rather than helices. The coupling to the structural chirality is provided by a magnetic axial vector, related to the so-called vector chirality. We show that this unique arrangement is the magnetic ground state of the symmetric-exchange Hamiltonian, based on ab initio theoretical calculations of the Heisenberg exchange interactions, and is stabilized by out-of-plane anisotropy. ${\mathrm{MnSb}}_{2}{\mathrm{O}}_{6}$ is predicted to be multiferroic with a unique ferroelectric switching mechanism.

The presence of ferroelectricity in hexagonal InMnO${}_{3}$ has been highly under debate. The results of our comprehensive experiments of low-temperature ($T$) polarization, transmission electron microscopy, and high-angle annular dark-field scanning TEM on well-controlled InMnO${}_{3}$ reveal that the ground state is ferroelectric with $P$6${}_{3}$$\mathit{cm}$ symmetry, but a nonferroelectric $P$$\overline{3}$$c$1 state exists at high $T$ and can be quenched to room temperature. We found that the competing ferroelectric and antiferroelectric phases coexist in mesoscopic scales and can be deliberately controlled by varying thermal treatments.

Selenium (Se) substitution drastically increases the transition temperature of iridium ditelluride (IrTe$_{2}$) to a diamagnetic superstructure from 278 K to 560 K. Transmission electron microscopy experiments revealed that this enhancement is accompanied by the evolution of non-sinusoidal structure modulations from $q = 1/5(10\bar{1})$- to $q = 1/6(10\bar{1})$-types. These comprehensive results are consistent with the concept of the destabilization of polymeric Te-Te bonds at the transition, the temperature of which is increased by chemical and hydrostatic pressure and by the substitution of Te with the more electronegative Se. This temperature-induced depolymerization transition in IrTe$_{2}$ is unique in crystalline inorganic solids., 5 pages, 4 figures, Phys. Rev. Lett. in press

We report on the observation of the hysteretic transition of a commensurate charge modulation in IrTe$_2$ from transport and scanning tunneling microscopy (STM) studies. Below the transition ($T_{\rm C} \approx 275$ K on cooling) a $q = 1/5$ charge modulation was observed, which is consistent with previous studies. Additional modulations [$q_n = (3n+2)^{-1}$] appear below a second transition at $T_{\rm S}\approx 180$ K on cooling. The coexistence of various modulations persist up to $T_{\rm C}$ on warming. The atomic structures of charge modulations and the temperature dependent STM studies suggest that 1/5 modulation is a periodic soliton lattice which partially melts below $T_{\rm S}$ on cooling. Our results provide compelling evidence that the ground state of IrTe$_2$ is a commensurate 1/6 charge modulation, which originates from periodic dimerization of Te atoms visualized by atomically resolved STM images., Comment: 5 pages, 5 figures

Although abundant research has focused recently on the quantum criticality of itinerant magnets, critical phenomena of insulating magnets in the vicinity of critical endpoints (CEP's) have rarely been revealed. Here we observe an emergent CEP at 2.05 T and 2.2 K with a suppressed thermal conductivity and concomitant strong critical fluctuations evident via a divergent magnetic susceptibility (e.g., chi''(2.05 T, 2.2 K)/chi''(3 T, 2.2 K)=23,500 %, comparable to the critical opalescence in water) in the hexagonal insulating antiferromagnet HoMnO3., Comment: 29 pages

Magnetic domains at the surface of a ferroelectric monodomain BiFeO3 single crystal have been imaged by hard X-ray magnetic scattering. Magnetic domains up to several hundred microns in size have been observed, corresponding to cycloidal modulations of the magnetization along the wave-vector k=2\pi(\delta,\delta,0) and symmetry equivalent directions. The rotation direction of the magnetization in all magnetic domains, determined by diffraction of circularly polarized light, was found to be unique and in agreement with predictions of a combined approach based on a spin-model complemented by relativistic density-functional simulations. Imaging of the surface shows that the largest adjacent domains display a 120 degree vortex structure., Comment: Published in Physical Review Letters

Electric field effect (EFE) controlled magnetoelectric transport in thin films of undoped and La-doped Sr$_{2}$IrO$_{4}$ (SIO) were investigated under the action of ionic liquid gating. Despite large carrier density modulation, the temperature dependent resistance measurements exhibit insulating behavior in chemically and EFE doped samples with the band filling up to 10\%. The ambipolar transport across the Mott gap is demonstrated by EFE tuning of the activation energy. Further, we observe a crossover from a negative magnetoresistance (MR) at high temperatures to positive MR at low temperatures. The crossover temperature was around $\sim$80-90 K, irrespective of the filling. This temperature and magnetic field dependent crossover is qualitatively associated with a change in the conduction mechanism from Mott to Coulomb gap mediated variable range hopping (VRH). This explains the origin of robust insulating ground state of SIO in electrical transport studies and highlights the importance of disorder and Coulombic interaction on electrical properties of SIO.