Biferroic YCrO3

YCrO3 which has a monoclinic structure, shows weak ferromagnetism below 140 K (TN) and a ferroelectric transition at 473 K accompanied by hysteresis. We have determined the structure and energetics of YCrO3 with ferromagnetic and antiferromagnetic ordering by means of first-principles density functional theory calculations, based on pseudopotentials and a plane wave basis. The non-centrosymmetric monoclinic structure is found to be lower in energy than the orthorhombic structure, supporting the biferroic nature of YCrO3.Comment: 16 pages including figure

Multiferroic nature of charge-ordered rare earth manganites

Charge-ordered rare earth manganites Nd0.5Ca0.5MnO3, La0.25Nd0.25Ca0.5MnO3, Pr0.7Ca0.3MnO3 and Pr0.6Ca0.4MnO3 are found to exhibit dielectric constant anomalies around the charge-ordering or the magnetic transition temperatures. Magnetic fields have a marked effect on the dielectric properties, indicating the presence of coupling between the magnetic and electrical order parameters. The observation of magnetoferroelectricity in these manganites is in accord with the recent theoretical predictions of Khomskii and coworkers

Atomic-scale control of magnetic anisotropy via novel spin-orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices

Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e. magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry. Extrinsic control over the MA is usually achieved by introducing shape anisotropy or exchange bias from another magnetically ordered material. Here we demonstrate a pathway to manipulate MA of 3d transition metal oxides (TMOs) by digitally inserting non-magnetic 5d TMOs with pronounced spin-orbit coupling (SOC). High quality superlattices comprised of ferromagnetic La2/3Sr1/3MnO3 (LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control of thickness at atomic scale. Magnetic easy axis reorientation is observed by controlling the dimensionality of SIO, mediated through the emergence of a novel spin-orbit state within the nominally paramagnetic SIO.Comment: Proceedings of the National Academy of Sciences, May 201

Interface engineering of domain structures in BiFeO3 thin films

A wealth of fascinating phenomena have been discovered at the BiFeO3 domain walls, examples such as domain wall conductivity, photovoltaic effects, and magnetoelectric coupling. Thus, the ability to precisely control the domain structures and accurately study their switching behaviors is critical to realize the next generation of novel devices based on domain wall functionalities. In this work, the introduction of a dielectric layer leads to the tunability of the depolarization field both in the multilayers and superlattices, which provides a novel approach to control the domain patterns of BiFeO3 films. Moreover, we are able to study the switching behavior of the first time obtained periodic 109° stripe domains with a thick bottom electrode. Besides, the precise controlling of pure 71° and 109° periodic stripe domain walls enable us to make a clear demonstration that the exchange bias in the ferromagnet/BiFeO3 system originates from 109° domain walls. Our findings provide future directions to study the room temperature electric field control of exchange bias and open a new pathway to explore the room temperature multiferroic vortices in the BiFeO3 system

New routes to multiferroics

Multiferroic materials are those which possess both ferroelectric and ferromagnetic properties. Clearly, there is a contradiction here since ferromagnetism requires d-electrons while ferroelectricity generally occurs only in the absence of d-electrons. Several multiferroics demonstrating magnetoelectric coupling effects have, however, been discovered in the past few years, but they generally make use of alternative mechanisms in attaining these properties. Several new ideas and concepts have emerged in the past two years, typical of them being magnetic ferroelectricity induced by frustrated magnetism, lone pair effect, charge-ordering and local non-centrosymmetry. Charge-order driven magnetic ferroelectricity is interesting in that it would be expected to occur in a large number of rare earth manganites, Ln<SUB>1−x</SUB>A<SUB>x</SUB>MnO<SUB>3</SUB> (A=alkaline earth), well known for colossal magnetoresistance, electronic phase separation and other properties. In this article, we discuss novel routes to multiferroics, giving specific examples of materials along with their characteristics

Charge-order-driven multiferroic properties of Y<SUB>1&#8722;x</SUB>Ca<SUB>x</SUB>MnO<SUB>3</SUB>

Dielectric measurements on the charge-ordered insulators, Y1&#8722;xCaxMnO3 (x=0.4, 0.45 and 0.5), show maxima in the dielectric constant around the charge ordering transition temperature while magnetic measurements show the presence of weak ferromagnetic interactions at low temperatures. Besides the magnetic field dependence of the dielectric constant, these manganites also exhibit second harmonic generation. Thus, the charge-ordered Y1&#8722;xCaxMnO3 compositions are multiferroic and magnetoelectric, in accordance with theoretical predictions. Magnetoelectric properties are retained in small particles of Y0.5Ca0.5MnO3

InMnO<SUB>3</SUB>: a biferroic

InMnO3 which has a hexagonal structure similar to that of YMnO3 is found to show a canted antiferromagnetic behavior below 50 K (TN) and a ferroelectric (FE) transition at 500 K accompanied by hystersis. We have determined the structure, polarization, and energetics of the FE and paraelectric (PE) phases of InMnO3 using first-principles density functional theory calculations based on pseudopotentials and a plane-wave basis, and find the polarization of the PE phase to be a half-integer quantum. The difference in polarization of the FE and PE phases calculated along a simple path is different from the absolute value of polarization of the FE phase. A weak piezoelectric response is exhibited by InMnO3 to uniaxial strain

Ferroelectricity in Pb_1+δZrO₃ Thin Films

Antiferroelectric PbZrO₃ is being considered for a wide range of applications where the competition between centrosymmetric and noncentrosymmetric phases is important to the response. Here, we focus on the epitaxial growth of PbZrO₃ thin films and understanding the chemistry–structure coupling in Pb_1+δZrO₃ (δ = 0, 0.1, 0.2). High-quality, single-phase Pb_1+δZrO₃ films are synthesized via pulsed-laser deposition. Although no significant lattice parameter change is observed in X-ray studies, electrical characterization reveals that while the PbZrO₃ and Pb_1.1ZrO₃ heterostructures remain intrinsically antiferroelectric, the Pb_1.2ZrO₃ heterostructures exhibit a hysteresis loop indicative of ferroelectric response. Further X-ray scattering studies reveal strong quarter-order diffraction peaks in PbZrO₃ and Pb_1.1ZrO₃ heterostructures indicative of antiferroelectricity, while no such peaks are observed for Pb_1.2ZrO₃ heterostructures. Density functional theory calculations suggest the large cation nonstoichiometry is accommodated by incorporation of antisite Pb_Zr defects, which drive the Pb_1.2ZrO₃ heterostructures to a ferroelectric phase with <i>R</i>3<i>c</i> symmetry. In the end, stabilization of metastable phases in materials via chemical nonstoichiometry and defect engineering enables a novel route to manipulate the energy of the ground state of materials and the corresponding material properties