Search

Reviews the material aspects of the La1-xCaxMnO3 family of double-exchange ferromagnets. Low temperature regimes of the compound family; Transport, magnetic, thermal and acoustic response in the regimes.

Studies charge-ordered stripes in La1-xCaxMnO3 with x>0.5. Use of electron diffraction and electron microscopy. Modulation wave vector; Incommensurability of the charge ordering.

Presents measurements of electron paramagnetic resonance (EPR) at 9 and 35 GHz between 2 and 300 Kelvin in single crystals and powder samples of CuGeO[sub3]. Gyromagnetic factors for three principal axes; Interpretations on the resulting large decrease in the intensity of the copper&sup2+; EPR signal below 14 K; Details on the calculation of an opening of an energy gap.

Significant amount of emitted light from an organic light emitting diode (OLED) is trapped as a result of total internal reflection (TIR) on a glass-air interface. One of the strategies to increase the light extraction efficiency is using a scattering thin film. A model is built using the Monte Carlo ray tracing method to simulate Mie scattering. Almost 100% of light trapped by the TIR can be extracted if the radius of the spherical scatters, the refractive index ratio between the matrix and the scatter and the concentration of the scatter are optimized. The implication is important for a high efficiency OLED used in the next generation lighting source. [ABSTRACT FROM AUTHOR]

It has been common practice for physicists to assume electronic homogeneity when dealing with condensed matter properties. Recent experimental development, which have revealed fascinating properties of complex materials, demonstrate that such extraordinary macroscopic properties are often associated with microscopic-scale electronic/magnetic inhomogeneity, which limits the Hamitonian-type theoretical approach. Herein, we discuss the microscopic coexistence of metallic and insulating phases in novel materials having an intricate interplay among charge/spin/lattice degrees of freedom. Examples include the coexistence of superconducting-metallic and insulating phases in La2CuO4+δ as well as Mg1−xB2. The insulating nature in La2CuO4+δ originates from electron–electron correlation, but disorder plays a dominant role in producing the insulating behavior in Mg-deficient Mg1−xB2. We also examine the microscopic coexistence of ferromagnetic-metallic and charge-ordered-insulating phases in mixed-valent manganites, exhibiting colossal magnetoresistance. Possible origins of this electronic phase separation are discussed. [Copyright &y& Elsevier]

A mixture of a colossal magnetoresistance manganite (La5/8Sr3/8MnO3) and a multiferroic (LuMnO3), of potential interest for magnetoelectronics, was found to be bulk immiscible due to its structural/chemical incompatibility. Here, we demonstrate that thin-film epitaxy offers a route to achieve continuous perovskite solid solutions of such a bulk-immiscible mixture, allowing studies of their physical properties. The films grow with (110)- and (001)-preferred orientation on SrTiO3(100) and LaAlO3(100), respectively. The details of structural, magnetotransport, and magnetization data are discussed within the context of metal-insulator phase coexistence. Epitaxial stabilization of chemically immiscible phases clearly widens the scope of research on manganites as well as other materials. [ABSTRACT FROM AUTHOR]

The anomalous enhancement in dielectric (∈>6000) and piezoelectric constant (d[sub 33] > 600 pC/N) in the tetragonal side (χ=35%) of morphotropic phase boundary (MPB) has been observed in polycrystalline (1-χ)Pg(Mg[sub l/3]Nb[sub 2/3])O[sub 3]-χPbTiO[sub 3] (PMN-PT). On the other hand, x-ray peak position shifts under electric field (E) demonstrate that the intrinsic piezoelectric response becomes maximum at MPB (χ=33%-34%), which may be associated with the recently discovered monoclinic phase. Intensity change of Bragg peaks under E indicates that 90° domain rotation is the main contribution to additional strain in the tetragonal side of MPB, which dominates the intrinsic contribution of monoclinic phase in polycrystalline PMN-PT. [ABSTRACT FROM AUTHOR]

Presents research which observed low-field tunneling magnetoresistance in films of half-metallic CrO2 that were grown by high-pressure thermal decomposition of CrO3. High-temperature annealing treatments; Implications of research.

Proposes a technique for enhancing the magnetoresistive response of perovskite manganites using hetorostructures with soft magnets. Degree of enhancement achieved at room temperature; Use of (Mn,Zn)Fe[sub 2]O[sub 4] as the soft ferromagnet; Effectiveness of using the technique to design a magnetoresistive response for manganites in low fields.

Describes research which showed that low-field grain-boundary magnetoresistance can be realized in a non-perovskite magnetoresistive oxide, the pyrochlore Tl2Mn2O7. Magnetoresistance in perovskite manganites and its limitations; Modification of manganites by tunnelling; Benefits and explanation of low-field response.

Presents an abstract of a study on doped LaMnO[sub3] with fixed carrier concentration. Relationship between the Curie temperature and the average ionic radius of the lanthanum site; Lattice effects on magnetoresistance; Result of microstructural changes induced by composition, temperature, and pressure variations.

Presents an abstract of the study 'Single-Crystal Growth and Magnetic Properties of La[sub2]CuO[sub4] and Related Compounds (T,T*, and T' Phases),' by S.-W. Cheong.

Magnetic skyrmions offer promising prospects for constructing future energy-efficient and high-density information technology, leading to extensive explorations of new skyrmionic materials recently. The topological Hall effect has been widely adopted as a distinctive marker of skyrmion emergence. Alternately, here we propose a novel signature of skyrmion state by quantitatively investigating the magnetoresistance (MR) induced by skyrmionic bubbles in CeMn2Ge2. An intriguing finding was revealed: the anomalous MR measured at different temperatures can be normalized into a single curve, regardless of sample thickness. This behavior can be accurately reproduced by the recent chiral spin textures MR model. Further analysis of the MR anomaly allowed us to quantitatively examine the effective magnetic fields of various scattering channels. Remarkably, the analyses, combined with the Lorentz transmission electron microscopy results, indicate that the in-plane scattering channel with triplet exchange interactions predominantly governs the magnetotransport in the Bloch-type skyrmionic bubble state. Our results not only provide insights into the quantum correction on MR induced by skyrmionic bubble phase, but also present an electrical probing method for studying chiral spin texture formation, evolution, and their topological properties, which opens up exciting possibilities for identifying new skyrmionic materials and advancing the methodology for studying chiral spin textures. [ABSTRACT FROM AUTHOR]

We combine synchrotron-based infrared absorption and Raman scattering spectroscopies with diamond anvil cell techniques and first-principles calculations to explore the properties of hafnia under compression. We find that pressure drives HfO2:7%Y from the mixed monoclinic (P21=c) + antipolar orthorhombic (Pbca) phase to pure antipolar orthorhombic (Pbca) phase at approximately 6.3 GPa. This transformation is irreversible, meaning that upon release, the material is kinetically trapped in the Pbca metastable state at 300 K. Compression also drives polar orthorhombic (Pca21) hafnia into the tetragonal (P42=nmc) phase, although the latter is not metastable upon release. These results are unified by an analysis of the energy landscape. The fact that pressure allows us to stabilize targeted metastable structures with less Y stabilizer is important to preserving the flat phonon band physics of pure HfO2. [ABSTRACT FROM AUTHOR]

In order to explore the consequences of spin–orbit coupling on spin–phonon interactions in a set of chemically similar mixed metal oxides, we measured the infrared vibrational properties of Co 4 B 2 O9 (B = Nb, Ta) as a function of temperature and compared our findings with lattice dynamics calculations and several different models of spin–phonon coupling. Frequency vs temperature trends for the Co2+ shearing mode near 150 cm−1 reveal significant shifts across the magnetic ordering temperature that are especially large in relative terms. Bringing these results together and accounting for noncollinearity, we obtain spin–phonon coupling constants of −3.4 and −4.3 cm−1 for Co4Nb2O9 and the Ta analog, respectively. Analysis reveals that these coupling constants are derived from interlayer (rather than intralayer) exchange interactions and that the interlayer interactions contain competing antiferromagnetic and ferromagnetic contributions. At the same time, beyond-Heisenberg terms are minimized due to fortuitous symmetry considerations, different from most other 4d- and 5d-containing oxides. Comparison with other contemporary oxides shows that spin–phonon coupling in this family of materials is among the strongest ever reported, suggesting an origin for magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

Presents a study which performed high resolution photoemission measurements for the ferromagnetic transition of colossal magnetoresistance, mixed-valent manganese perovskite lanthanum[sub1-x]calcium[subx] manganese oxide. Samples and experimets; Collapse of band gap below the Curie temperature and the increase of density of states at the Fermi level upon cooling; Results of soft x-ray magnetic circular dichroism measurements.

Magnetically induced ferroelectric polarization in rare-earth RMn2O5 manganites is believed to originate from the symmetric exchange striction associated with a specific antiferromagnetic phase in the low temperature (T) region and would be irrelevant with electropoling in the high-T paramagnetic-paraelectric phase region. In this work, we demonstrate that low-T pyroelectric polarization of GdMn2O5 single crystals along the b axis in the antiferromagnetic phase exhibits remarkable dependence on the electropoling history imposed in the high-T paramagnetic-paraelectric phase. In particular, the high-T electropoling results in a reversal of ferroelectric polarization in the low-T region, which can be flopped back by the electropoling being sustained in the low-T ferroelectric region. The existence of an electrically polarizable magnetic cluster state in the high-T paramagnetic-paraelectric region is proposed based on a combination of experimental observations and first-principles calculations. An intrinsic correlation between the low-T antiferromagnetic ordering and the high-T polarizable state is discussed. The present experiments unveil the emergent phenomena on multiferroicity of RMn2O5 and suggest an alternative scenario for electrocontrol of magnetism. [ABSTRACT FROM AUTHOR]

Frustrated magnetic interactions in a quasi-two-dimensional {111} slab of pyrochlore lattice were studied. For uniform nearest neighbor (NN) interactions, we show that the complex magnetic problem can be mapped onto a model with two independent degrees of freedom, tricolor and binary sign. This provides a systematic way to construct the complex classical spin ground states with collinear and coplanar bipyramid spins. We also identify "partial but extended" zero-energy excitations amongst the ground states. For nonuniform NN interactions, the coplanar ground state can be obtained from the collinear bipyramid spin state by collectively rotating two spins of each tetrahedron with an angle a in an opposite direction. The latter model with α ∼ 30° fits the experimental neutron data from SrCr9pGa12-9pO19 well. [ABSTRACT FROM AUTHOR]

We applied dc voltage (V) to the LuFe2O4 single crystal and measured the V-dependent optical reflectivity. As V increases, an optical absorption band appears at the mid-infrared frequency range which we could identify as resulting from the dc electric (E) field. We discuss possible connection of this novel electro-optical effect with the strongly correlated states in LuFe2O4. In the mean time, a reflectivity level change is seen in the IR ∼ visible frequency range by the V application due to the Joule heating of the sample. [ABSTRACT FROM AUTHOR]

We discuss uniaxial optical anisotropy in single-crystal BiFeO3 determined by spectroscopic ellipsometry from 1.0 to 5.5 eV. The dielectric function ϵ = ϵ1 + iϵ2 and refractive index N = n + ik spectra of BiFeO3 are extracted for the tensor components along its ordinary and extraordinary principal axes. Using the standard line-shape analysis, we also obtain the energies of the major optical structures associated with the charge-transfer transitions in BiFeO3. [ABSTRACT FROM AUTHOR]

Piezoresponse force microscopy (PFM) has emerged as a powerful tool for research in ferroelectric and piezoelectric materials. While the vertical PFM (VPFM) mode is well understood and applied at a quantitative level, the lateral PFM (LPFM) mode is rarely quantified, mainly due to the lack of a practical calibration methodology. Here by PFM imaging on a LiNbO3 180° domain wall, we demonstrate a convenient way to achieve simultaneous VPFM and LPFM calibrations. Using these calibrations, we perform a full quantitative VPFM and LPFM measurement on a (001)-cut PbTiO3 single crystal. The measured effective piezoelectric coefficients def f 33 and def f 35 together naturally provide more information on a material's local tensorial electromechanical properties. The proposed approach can be applied to a wide variety of ferroelectric and piezoelectric systems. [ABSTRACT FROM AUTHOR]

Presents research which reported a different pattern of charge localization in the charge-ordered phase of a kind of manganese oxide. Stripe phases in systems of charge and spin; Physics of high-temperature superconductors; Static charge stripes in manganese oxides; Form of stripe pattern; Paired Jahn-Teller stripes; Implications for magnetic and transport properties of manganese oxides.

We report the discovery of finite length scale effects on vibronic coupling in nanoscale α-Fe2O3 as measured by the behavior of vibronically activated d-d on-site excitations of Fe3+ as a function of size and shape. An oscillator strength analysis reveals that the frequency of the coupled symmetry-breaking phonon changes with size, a crossover that we analyze in terms of increasing three-dimensional character to the displacement pattern. These findings demonstrate the flexibility of mixing processes in confined systems and suggest a strategy for both enhancing and controlling charge-lattice interactions in other materials. [ABSTRACT FROM AUTHOR]

Cryogenic-temperature technology is a promising and practical solution for the intense demand for high performance electronics. By utilizing the unique hysteretic behavior of perovskite (La,Pr,Ca)MnO3 observed either as a function of temperature and/or applied electric fields, we discovered low-temperature phases with either metallic and/or insulating resistance values. Low temperature resistivity state can be repeatedly switched by applying various voltage pulses. Resistance value of each phase is stable in time and reproducible after many switching cycles. Phases with intermediate resistance values can also be repeatedly stabilized. The behaviors reported here can be harnessed for cryogenic-temperature phase-change random access memory applications. [ABSTRACT FROM AUTHOR]

We detected broadband coherent terahertz emission from multiferroic BiFeO3 after illuminating a high-quality bulk single ferroelectric domain crystal with an ∼100 fs optical pulse. The dependence of the emitted terahertz waveform on the energy and polarization of the optical pulse is consistent with the optical rectification mechanism of terahertz emission. We also report room-temperature terahertz optical constants of BiFeO3. [ABSTRACT FROM AUTHOR]

Single crystals of multiferroic BiFeO3 were investigated using neutron scattering. Application of an electric field reversibly switches ferroelastic domains, inducing changes in the magnetic structure which follows rotation of the structural domains. In addition, electric fields can be used to control the populations of the equivalent magnetic domains within a single ferroelastic domain, possibly via field-induced strain. [ABSTRACT FROM AUTHOR]

By using high-pressure heat treatment, we synthesized the single perovskite phase of polycrystalline (1-x)PbZn[sub 1/3]Nb[sub 2/3]O[sub 3]-xPbTiO[sub 3] which was reported to show giant piezoelectricity in crystal forms. Piezoelectric constant of the polycrystalline materials at room temperature was found to become maximum at the rhombohedral side (x=8%) of morphotropic phase boundary. Microscopic strain under the electric field (E) along different crystallographic directions was identified by observing the x-ray Bragg peak shift of polycrystalline samples with E. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Measurements of the structure of hexagonal RMnO3 [R = rare earths (Ho) and Y] for temperatures significantly above the ferroelectric transition temperature (TFE) were conducted to determine the nature of the transition. The local and long range structural measurements were complemented by ab initio molecular dynamics simulations. With respect to the Mn sites in YMnO3 and HoMnO3, we find no large atomic (bond distances or thermal factors), electronic structure changes, or rehybridization on crossing TFE from local structural methods. The local symmetry about the Mn sites is preserved. With respect to the local structure about the Ho sites, a reduction of the average Ho-O bond with increased temperature is found. Ab initio molecular dynamics calculations on HoMnO3 reveal the detailed motions of all ions. Above ∼900 K there are large displacements of the Ho, O3, and O4 ions along the z axis which reduce the buckling of the MnO3/O4 planes. The changes result in O3/O4 ions moving to toward central points between pairs of Ho ions on the z axis. These structural changes make the coordination of Ho sites more symmetric thus extinguishing the electric polarization. At significantly higher temperatures, rotation of the MnO5 polyhedra occurs without a significant change in electric polarization. The Born effective charge tensor is found to be highly anisotropic at the O sites but does not change appreciably at high temperatures. [ABSTRACT FROM AUTHOR]

The local structure of the parent and doped LaFeAsO1-xFx (pnictide) compounds were studied by x-ray absorption spectroscopy and density functional methods. In the doped system, the Fe-As and Fe-Fe correlations are both well modeled by an Einstein model. For the Fe-As bonds, the Einstein temperatures are identical for the doped (11%) and undoped samples but the doped sample is found to have a lower level of static disorder. Doping is found to increases the effective Einstein temperature of Fe-Fe atomic correlation. The results suggest that the onset of superconductivity in the F doped system may be related to enhanced magnetic interactions. Density functional calculations of the total charge density reveal strong bonding between neighboring As ions but metal-like behavior in the Fe layers. It is also seen directly that the replacement of oxygen by fluorine modifies the electron charge density mainly on the Fe sites. [ABSTRACT FROM AUTHOR]

We have investigated the details of phase separation in the electron-doped manganites Sm1-xCaxMnO3 (0.8≤x≤0.92) by using temperature dependent x-ray diffraction. The lattice of the low-temperature orthorhombic phase is distorted to various extents according to the strength of the coexisting monoclinic phase. Meanwhile, the room-temperature lattice becomes more distorted due to the increasing Jahn–Teller active Mn3+ ions by Sm3+ doping. On the other hand, the substitution of Ca2+ with Sm3+ introduces the Mn3+–Mn4+ pairs, which favor the double exchange ferromagnetism. As a result of the competition between the lattice distortion and electron doping level, the modified phase diagram have been presented, including the high-temperature Griffiths phase and the ground state with competing multiphases. [ABSTRACT FROM AUTHOR]

We report a sequent phase transition using high-resolution synchrotron x-ray scattering in a single crystal Nd1/2Sr1/2MnO3. By measuring the peak profile of Bragg reflections, upon cooling, we observed an increase in the width of the Bragg reflections around the Curie temperature (252 K) corresponding to the transition from a paramagnetic to a ferromagnetic state. Below approximately 200 K, dramatic changes in the width and integrated intensity were observed. Changes continued until the formation of charge ordering with q=(12,0,0) at TCO=152 K. This charge ordering was observed to be the first order transition with a large hysteresis width of 10 K. This sequent transition is understood by the formation of different magnetic domains at different temperature ranges as that observed by neutron powder diffraction. [ABSTRACT FROM AUTHOR]

Hexagonal HoMnO3 is a frustrated antiferromagnet (TN=72 K) ferroelectric (TC=875 K) with a rich magnetic phase diagram consisting of multiple temperature- and field-dependent phases. Previously observed anomalies in the dielectric constant at magnetic phase transitions indicate strong coupling between the ferroelectricity and magnetism. Neutron-diffraction measurements in a magnetic field reveal new intermediate-field phases at low temperatures. Inelastic neutron-scattering measurements are used to establish the primary magnetic interactions and demonstrate that the spin dynamics in HoMnO3 are well described by a simple two-dimensional nearest-neighbor Heisenberg antiferromagnetic exchange J=2.44 meV and a temperature-dependent anisotropy D. [ABSTRACT FROM AUTHOR]

Thin films of Sr[sub 2]FeMoO[sub 6] have been deposited on single-crystalline and polycrystalline SrTiO[sub 3] substrates by pulsed laser deposition from a stoichiometric target. In order to obtain high-quality films, the deposition parameters were systematically optimized. The films grown under optimized conditions show properties comparable to those of bulk Sr[sub 2]FeMoO[sub 6] single crystals. Surprisingly, polycrystalline films obtained by depositing on polycrystalline SrTiO[sub 3] substrates do not show any significant low-field magnetoresistance (MR), contrary to expectations for a spin-polarized material. However, after controlled annealing-induced alteration of the grain-boundary properties, a development of the low-field MR feature is clearly observed. The occurrence of the low-field MR is accompanied by nonlinearity in the current-voltage characteristics. These results are analyzed in the light of the prevalent understanding of the properties of this double perovskite material. [ABSTRACT FROM AUTHOR]

Examines the importance of strain in the magnetic anisotropy of manganite thin films. Explanation for the film symmetries; Dependence of magnetic properties on the film thickness; Generation of magnetization measurements on a Lakeshore vibrating sample magnetometer.

Presents an abstract of an article on inelastic neutron scattering investigations of magnetic excitations in lanthanum cuprate.

The protected electron states at the boundaries or on the surfaces of topological insulators (TIs) have been the subject of intense theoretical and experimental investigations. Such states are enforced by very strong spin-orbit interaction in solids composed of heavy elements. Here, we study the composite particles--chiral excitons--formed by the Coulomb attraction between electrons and holes residing on the surface of an archetypical 3D TI, Bi2Se3. Photoluminescence (PL) emission arising due to recombination of excitons in conventional semiconductors is usually unpolarized because of scattering by phonons and other degrees of freedom during exciton thermalization. On the contrary, we observe almost perfectly polarization-preserving PL emission from chiral excitons. We demonstrate that the chiral excitons can be optically oriented with circularly polarized light in a broad range of excitation energies, even when the latter deviate fromthe (apparent) optical band gap by hundreds of millielectronvolts, and that the orientation remains preserved even at room temperature. Based on the dependences of the PL spectra on the energy and polarization of incident photons, we propose that chiral excitons are made from massive holes and massless (Dirac) electrons, both with chiral spin textures enforced by strong spin-orbit coupling. A theoretical model based on this proposal describes quantitatively the experimental observations. The optical orientation of composite particles, the chiral excitons, emerges as a general result of strong spin-orbit coupling in a 2D electron system. Our findings can potentially expand applications of TIs in photonics and optoelectronics. [ABSTRACT FROM AUTHOR]

A temperature dependent Raman scattering study in multiferroic single crystals RMn2O5 (R=Bi, Eu, and Dy) was performed. The Raman spectra were measured in the range from 150 to 450 cm-1 involving mostly Mn–O–Mn bending vibrations, complementing our previous work in a higher frequency range involving Mn–O stretching modes. A number of studied phonons present anomalous frequency behavior below a characteristic temperature, T*∼60–65 K, such as that found for the stretching modes. The sign and magnitude of such anomalous behavior appear to be correlated with the ionic radius of R, being softening for R=Bi and hardening for R=Eu and Dy in the range between TC/TN and T*. The anomalous phonon behaviors in both bending and stretching modes are consistent with an interpretation in terms of the spin-phonon coupling in a scenario of strong magnetic correlations. [ABSTRACT FROM AUTHOR]

The complex conductive behavior of ferroelectric domain walls is attracting more and more attention for their potential application as an independent nanoelectronic component. For the (001) epitaxial BiFeO3 films, we find that the domain wall conductivity varies among 71° domain walls, with tail-to-tail (T-T) domain walls more conductive than head-to-head (H-H) and head-to-tail (H-T) ones. Furthermore, it is observed that most of the conductive areas are composed of two parallel lines around the T-T domain walls. These experimental results can be well simulated by our theoretical model based on the polarization configuration and a tunneling mechanism. Our work will help to understand the mechanism of domain wall conductance in ferroelectric materials and further promote the usage of domain walls in advanced nano-devices. [ABSTRACT FROM AUTHOR]

Thermal expansion measurements were done on single-crystal RMn2O5 (R=Tb,Dy,Ho) along the principal crystallographic axes. Distinctive anomalies were observed in the linear thermal expansivities at critical temperatures marking the onset of long-range antiferromagnetic order (TN1), ferroelectricity (TC1), as well as at temperatures when anomalous changes in the polarization, dielectric constant, and spin wave incommensurability have been previously reported. These observations suggest that the coupling between the magnetic orders and the dielectric properties is mediated by the lattice distortion. In particular, a possible scenario as to how ferroelectricity arises and subsequently is altered as a result of the subtle changes in the highly frustrated magnetic order, is discussed in the light of the strong spin-lattice coupling observed in these materials. Neutron diffraction measurements on HoMn2O5 show a spin reorientation at 23 K corresponding to a step-like anomaly in the dielectric constant. [ABSTRACT FROM AUTHOR]

The crystallographic and magnetic properties of HoMn0.9957Fe0.01O3 powder have been studied by x-ray diffraction, superconducting quantum interference device measurements, and Mössbauer spectroscopy. It has a hexagonal space group P63cm with the lattice constants a0=6.139 and c0=11.402 Å at room temperature. The magnetic susceptibility follows a Curie–Weiss law behavior, where the Curie–Weiss temperature was determined to be θCW=-18 K. The Mössbauer spectra below TN=72 K exhibit the six-line patterns, which coalesce into two lines above TN. The electric quadrupole splitting value at TN was ΔEQ=1.79±0.01 mm/s. An important point can be accessed that the direct observation of a coupling for the electric and magnetic order parameters was possible by Mössbauer spectroscopy. [ABSTRACT FROM AUTHOR]

Results of studies of the susceptibility, magnetic specific heat, and electron paramagnetic resonance spectrum of the geometrically frustrated antiferromagnetic ZnCr[sub 2]O[sub 4] are presented. The temperature dependence of the susceptibility and the specific heat are in good agreement with the predictions of the quantum tetrahedral mean field model for exchange-coupled spin-3/2 ions on a pyrochlore lattice. The origin of the anomalous behavior of the resonance intensity below 90 K is discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Transmittance spectra of TbFeO3 single crystals have been studied in the far-infrared spectral range 15-120cm-1 in the external magnetic fields up to 9 T and at low temperatures down to 1.5 K. The temperature and magnetic-field dependencies of the antiferromagnetic resonance (AFMR) modes have been measured below and above the magnetic ordering temperature of Tb moments TNTb=3.3K. Both the quasiferromagnetic and quasiantiferromagnetic modes of AFMR demonstrate hardening at T

Investigates the electron spin resonance and magnetic properties in perovskite and pyrochlore manganites. Preparation of ceramic samples of La0.67Ca0.33MnO3; Description of the ferromagnetic interaction between manganese (Mn) ions in colossal magnetoresistence perovskites using double exchange interaction; Results of the investigation.

Presents a study that investigated the relationship between weak ferromagnetism, superconductivity, and lattice parameter in the A[sub2-x-y]B[subx]Ce[suby]CuO[sub4] (A,B...La, Pr, Nd, Sm, Eu, Gd, Y) compounds. Information on ac susceptibility as a function of temperature of Eu[sub1.8]Y[sub02]CuO[sub4]; Spectra for Sm[sub2-x]Y[subx]CuO[sub4] measured at 9Ghz and 263 Kelvin; Analysis of dc susceptibility measured at 10 Oe on a powder sample of La[sub1.1]Gd[0.75]Ce[sub0.15]CuO[sub4].

Presents a study of the magnetic and structural properties of a single crystal of neodymium[sub2] copper oxygen[sub4]. Results for copper and neodymium spin ordering; Structural distortion.

Hybrid improper ferroelectrics have their electric polarization generated by two or more combined non-ferroelectric structural distortions, such as the rotation and tilting of Ti-O octahedral in the Ca3Ti2O7 (CTO) family. In this work, we prepare the high quality (010)-oriented CTO thin films on (110) SrTiO3 (STO) substrates by pulsed laser deposition. The good epitaxial growth of the CTO thin films on the substrates with the interfacial epitaxial relationship of [001]CTO//[001]STO and [100]CTO//[-110]STO is revealed. The in-plane ferroelectric hysteresis unveils an ultralow coercive field of ~5 kV/cm even at low temperature, nearly two orders of magnitude lower than that of bulk CTO single crystals. The huge difference between the epitaxial thin films and bulk crystals is most likely due to the lattice imperfections in the thin films rather than substrate induced lattice strains, suggesting high sensitivity of the ferroelectric properties to lattice defects. [ABSTRACT FROM AUTHOR]

We report the discovery of a metamagnetic phase transition in a polar antiferromagnet Ni3TeO6 that occurs at 52 T. The new phase transition accompanies a colossal magnetoelectric effect, with a magneticfield- induced polarization change of 0.3 μC/cm2, 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. [ABSTRACT FROM AUTHOR]

Multiferroics permit the magnetic control of the electric polarization and the electric control of the magnetization. These static magnetoelectric (ME) effects are of enormous interest; The ability to read and write a magnetic state current-free by an electric voltage would provide a huge technological advantage. Dynamic or optical ME effects are equally interesting, because they give rise to unidirectional light propagation as recently observed in low-temperature multiferroics. This phenomenon, if realized at room temperature, would allow the development of optical diodes which transmit unpolarized light in one, but not in the opposite, direction. Here, we report strong unidirectional transmission in the room-temperature multiferroic BiFe03 over the gigahertz-terahertz frequency range. The supporting theory attributes the observed unidirectional transmission to the spin-current-driven dynamic ME effect. These findings are an important step toward the realization of optical diodes, supplemented by the ability to switch the transmission direction with a magnetic or electric field. [ABSTRACT FROM AUTHOR]

LuFe2O4 is a multiferroic system which exhibits charge order, ferroelectricity, and ferrimagnetism simultaneously below ~230 K. The ferroelectric/charge order domains of LuFe2O4 are imaged with both piezoresponse force microscopy (PFM) and electrostatic force microscopy (EFM), while the magnetic domains are characterized by magnetic force microscopy (MFM). Comparison of PFM and EFM results suggests that the proposed ferroelectricity in LuFe2O4 is not of usual displacive type but of electronic origin. Simultaneous characterization of ferroelectric/charge order and magnetic domains by EFM and MFM, respectively, on the same surface of LuFe2O4 reveals that both domains have irregular patterns of similar shape, but the length scales are quite different. The domain size is approximately 100 nm for the ferroelectric domains, while the magnetic domain size is much larger and gets as large as 1 μm. We also demonstrate that the origin of the formation of irregular domains in LuFe2O4 is not extrinsic but intrinsic. [ABSTRACT FROM AUTHOR]

We have explored the origin of unusual first-order-type electronic and structural transitions in IrTe2, based on the first-principles total energy density functional theory analysis. We have clarified that the structural transition occurs through the interplay among the charge density wavelike lattice modulation with q1/5=(1/5,0,1/5), in-plane dimer ordering, and the uniform lattice deformation. The Ir-Ir dimer formation via a molecular-orbital version of the Jahn-Teller distortion in the Ir-Ir zigzag stripe is found to play the most important role in producing the charge disproportionation state. Angle-resolved photo-emission spectroscopy reveals the characteristic features of structural transition, which are in good agreement with the density functional theory bands obtained by the band-unfolding technique. [ABSTRACT FROM AUTHOR]