Magnetoelectric Properties Research Articles

Dimensional Control of Octahedral Tilt in SrRuO3 via Infinite-Layered Oxides.

Manipulation of octahedral distortion at atomic scale is an effective means to tune the ground states of functional oxides. Previous work demonstrates that strain and film thickness are variable parameters to modify the octahedral parameters. However, selective control of bonding geometry by structural propagation from adjacent layers is rarely studied. Here we propose a new route to tune the ferromagnetism in SrRuO3 (SRO) ultrathin layers by oxygen coordination of adjacent SrCuO2 (SCO) layers. The infinite-layered CuO2 exhibits a structural transformation from "planar-type" to "chain-type" with reduced film thickness. Two orientations dramatically modify the polyhedral connectivity at the interface, thus altering the octahedral distortion of SRO. The local structural variation changes the spin state of Ru and orbital hybridization strength, leading to a significant change in the magnetoresistance and anomalous Hall resistivity. These findings could launch investigations into adaptive control of functionalities in quantum oxide heterostructures using oxygen coordination.

Mn0.7Zn0.3Fe2O4 + BaTiO3 composites: structural, morphological, magnetic, M–E effect and dielectric properties

Here in the present investigation, constituent phases of (1 − x)Mn0.7Zn0.3Fe2O4(MZFO) + (x)BaTiO3(BTO) (where x = 0.0, 0.25, 0.50, 0.75 and 1.0) composites have been synthesized by sol–gel auto-ignition route and the composite structure by ceramic route. The XRD analysis ensures that the composite structure consists of both cubic spinel piezomagnetic and perovskite piezoelectric phases. The average crystallite size estimated from Scherrer equation increases from 15.36 to 21.94 nm. The strain induced in individual phases has been investigated by W–H analysis and it is observed that the MZFO phase shows comprehensive type strain while BTO phase shows tensile type strain. Scanning electron micrographs confirm the microstructure of the sample with grain size ranges from 36.006 to 54 nm. Energy dispersive X-ray spectra and elemental color mappings of typical samples (x = 0.0 and 0.75) clearly indicates the phase purity and stoichiometric proportion of the composites. Fourier transform infrared spectra showed five major absorption bands related to stretching vibrations of different kinds of metal ions and oxygen ions. Increasing percentage of BTO phase in the composite reduces the saturation magnetization, remnant magnetization and coercivity. Real and imaginary parts of permittivity show maximum values at lower frequency region and decrease with increase in applied frequency. For the composition (0.25)MZFO–(0.75)BTO, composite shows maximum value of magnetoelectric coupling coefficient (αME = 20.45 mVcm−1 Oe−1). The improved magnetoelectric properties make MZFO–BTO composite applicable for electronic devices.

High-resolution optical spectroscopy, magnetic properties, and single-crystal neutron diffraction of multiferroic HoFe3(BO3)4 : Magnetic structure

The magnetic structure is usually determined by the neutron diffraction measurements. However, in the case of complex multisublattice magnetics, this method fails to give an unambiguous result. Here, on the example of multiferroic ${\mathrm{HoFe}}_{3}{({\mathrm{BO}}_{3})}_{4}$, we show that in the case of rare-earth (RE) compounds the right magnetic structure can be determined by additionally using optical spectroscopy and a theoretical analysis based on spectroscopic data. ${\mathrm{HoFe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ demonstrates a series of phase transitions and interesting magnetic and magnetoelectric properties. The available information on the magnetic structure of the compound, necessary for understanding and utilizing these properties, is contradictory. To resolve the existing ambiguities, we apply a combined approach. The high-resolution spectroscopy data deliver a set of the ${\mathrm{Ho}}^{3+}$ crystal-field (CF) levels in the paramagnetic and both easy-plane and easy-axis magnetic phases. These data are used to determine CF and ${\mathrm{Ho}}^{3+}\text{\ensuremath{-}}{\mathrm{Fe}}^{3+}$ exchange parameters and, then, to calculate the temperature dependencies of the magnetic susceptibility tensor of ${\mathrm{HoFe}}_{3}{({\mathrm{BO}}_{3})}_{4}$. Based on these calculations, we suggest an easy-plane antiferromagnetic structure with a collinear arrangement of the Fe spins along the $a$ axis and induced noncolinear moments of magnetically nonequivalent Ho ions. The suggested structure is further confirmed by single-crystal elastic neutron scattering experiments. We argue that specific features of the magnetic properties of RE iron borates isostructural to ${\mathrm{HoFe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ are governed by the energy patterns and the symmetry properties of the wave functions of the lower CF levels of the RE ground multiplet in the crystal field of the ${C}_{2}$ symmetry.

Effect of Al2O3 Addition on Magnetoelectric Properties of Ni0.5Zn0.5Fe2O4/Ba0.8Sr0.2TiO3 Composite Ceramics

Effect of Al2O3 Addition on Magnetoelectric Properties of Ni0.5Zn0.5Fe2O4/Ba0.8Sr0.2TiO3 Composite Ceramics

Influence of phase dominance on structural, magneto-dielectric, magnetic-electric properties of (Ba0.85Ca0.15Zr0.1Ti0.9)O3-CoFe2O3 composites

In this work, lead-free (1-x) Ba0.85Ca0.15Zr0.1Ti0.9)O3–xCoFe2O3 (BCZT-CFO, x = 00, 0.2,0.8 and 1) multiferroic composites have been prepared by chemical solution technique and sintered at 1300 °C. The article is focused on a systematic study of phase dominance effect on structure, microstructure, dielectric, magneto-dielectric, magnetic, electric, and magneto-electric properties of the BCZT-CFO composites. The XRD study confirms perovskite phase in BCZT, cubic spinal phase in CFO and mixed structural evolution in composite samples without any traceable secondary phase formation. William-Hall equation has been used to evaluate strain kinetics in pure and composite samples. The scanning electron micrographs show dispersion of smaller BCZT grains in larger CFO grains matrix. The dense microstructure has been observed for composite sample with ferrite phase dominance. The room temperature dielectric study reveals frequency-dependent dielectric dispersion characteristics for composites and pure CFO. The enhanced dielectric properties are observed for composite sample with ferroelectric phase dominance. The room temperature magneto-dielectric behavior has been observed for lead-free multiferroic composites. Under magnetic study, observed typical ferromagnetic M-H hysteresis loop reveals presence of long-range ferromagnetic ordering in pure CFO as well as in composite samples. The highest value of Ms ~ 38.2 emu/g and Mr = 1.2 emu/g has been measured for ferrite phase dominant composite sample. Higher coercive field Hc value has been observed for composite with ferroelectric phase dominance. Leakage current characteristic has been investigated at and above room temperature for prepared samples. The composite with ferrite phase dominance has shown higher leakage current characteristics. The enhanced magento-electric coupling coefficient has been measured for composite with higher ferrite phase concentration.

Magnetoelectric and multiferroic properties of spinels

In the last two decades, significant progress has been made in combining ferroelectricity and magnetism in the same material. Usually, magnetism and ferroelectricity were thought of as independent phenomena. However, the discovery of spin-induced ferroelectricity with a strong coupling between magnetism and electric polarization is intriguing. Whether they interact non-trivially is determined by the symmetries of the crystal lattice and the appearing magnetic structure, which, in turn, depends on the nature of magnetic ions, their exchange, and anisotropic interactions, the presence of frustration, etc. Several structural families of compounds exhibiting magnetoelectric (ME) or multiferroic properties have already been reported. This paper gives an account of the richness of structure, magnetism, magnetoelectric and multiferroic properties of spinels. After presenting symmetry aspects of the crystal and magnetic structures of spinels related to these phenomena, we give several examples of magnetoelectric and multiferroic spinels explaining the relations between magnetism and electric polarization and discuss their future perspectives.

Bipolar Conduction and Giant Positive Magnetoresistance in Doped Metallic Titanium Oxide Heterostructures

AbstractEmpowering conventional materials with unexpected magnetoelectric properties is appealing to the multi‐functionalization of existing devices and the exploration of future electronics. Recently, owing to its unique effect in modulating a matter's properties, ultra‐small dopants, for example, H, D, and Li, attract enormous attention in creating emergent functionalities, such as superconductivity, and metal–insulator transition. Here, an observation of bipolar conduction accompanied by a giant positive magnetoresistance in D‐doped metallic Ti oxide (TiOxDy) films is reported. To overcome the challenges in intercalating the D into a crystalline oxide, a series of TiOxDy is formed by sequentially doping Ti with D and surface/interface oxidation. Intriguingly, while the electron mobility of the TiOxDy increases by an order of magnitude larger after doping, the emergent holes also exhibit high mobility. Moreover, the bipolar conduction induces a giant magnetoresistance up to 900% at 6 T, which is ≈6 times higher than its conventional phase. This study paves a way to empower conventional materials in existing electronics and induce novel electronic phases.

Magnetic and electric properties of multiferroic LiFeP2O7. Comparison with LiCrP2O7

The temperature and magnetic field dependence of the magnetic and electric properties of LiFeP2O7 (LFPO) and LiCrP2O7 (LCPO) are studied using a microscopic model and the Green’s function technique. We have shown that LFPO is antiferromagnetic, but shows a weak ferromagnetism along the [Formula: see text] axis which originates from the canted antiferromagnetic order. For LCPO, such a ferromagnetic order along the [Formula: see text] axis is not observed. In the temperature dependence of the electrical polarization [Formula: see text] along the [Formula: see text] axis there is a kink at [Formula: see text] K which is an indirect evidence for the intrinsic magnetoelectric effect in LFPO. Applying an external magnetic field [Formula: see text], the polarization [Formula: see text] increases, stronger for small temperatures and the kink at [Formula: see text] disappears. For LCPO, we do not obtain a kink at [Formula: see text] K. LCPO is polar, but not ferroelectric. We can conclude that the missing magnetoelectric properties in LCPO could be due to the differences in the magnetic orders between LFPO and LCPO.

Prediction of tunable magnetoelectric properties in compositionally graded ferroelectric/ferromagnetic laminated nanocomposites

The advent of modern thin-film deposition approaches has ushered in a new era of designed materials with well-controlled composition distributions, e.g., compositionally graded ferroelectric (CGFE) thin films, and thereby, it is readily accessible CGFE/FM (ferromagnetic) multilayer thin films. Being recognized this emerging class of materials, in this study, we develop a phase-field model based on the Ginzburg–Landau theory that takes into account the gradient of ferroelectric (FE) compositions in order to predict material properties of CGFE/FM thin films. The developed phase-field model is applied to investigate the effect of the FE composition gradient on magnetoelectric (ME) coupling of graded Pb(1−x)SrxTiO3/CoFe2O4 laminated nanocomposites. Two types of composition gradients are considered: inward (O-type) and outward (X-type) gradients. Unusual polarization domain structures with curved domain walls are formed in CGFE layers, which are governed by the composition gradients and distinct from typical stripe domains in homogeneous counterparts. As a result, the ME effect is strongly dependent on the composition gradient. Particularly, the ME coupling in the O-type nanocomposites increases with the increasing composition gradient, while it decreases in the X-type ones. The dependence of ME coupling on the composition gradient originates from the distinguishable energy distributions in O-type and X-type nanocomposites. This work, therefore, provides a strategy to design the ME effect via the configuration of the composition gradient.

Enhanced magnetoelectric coupling characteristics of Mn2O3-modified BiFeO3-based ceramics

BiFeO3 is the most important room-temperature multiferroic material. However, the magnetoelectric coupling effect of BiFeO3 is weak, and an effective way to improve it is to suppress the spin cycloid structure. In this work, Mn ions were substituted into BiFeO3-based ceramics to enhance the magnetoelectric coupling effect. All samples were refined with the rhombohedral R3c structure. The grain size gradually decreased with increasing Mn substitution content. According to DSC analysis, the endothermic peak and exothermic peak exhibit an obvious thermal hysteresis behavior, indicating that it is the first-order ferroelectric transition. Meanwhile, a dielectric anomaly was also found at that transition temperature. The leakage current increased with increasing Mn content, which can be ascribed to the increased oxygen vacancies. The magnetic properties were enhanced for all samples, and the maximum Mr = 51.9 emu/mol was obtained for x = 0.03. In addition, the magnetoelectric properties were improved, and the value of linear magnetoelectric coefficient exhibits a maximum value αME = 0.38 mV/cm Oe at x = 0.03. Thus, the addition of Mn at Fe sites may destroy the spin cycloid structure and enhance the ME effect of BiFeO3.

Emergence of room temperature stable skyrmionic bubbles in the rare earth based REMn2Ge2 (RE = Ce, Pr, and Nd) magnets

Skyrmionic spin configurations, including skyrmions and skyrmionic bubbles, have attracted much attention for their intriguing magneto-electrical properties. To date, most skyrmionic spin configurations are observed in transition metal based magnets, the correlations between topological structures and f orbital electrons are still unclear due to the lack of rare earth (RE) based magnets hosting skyrmionic spin configurations, especially at room temperature. Here, a family of RE-based intermetallics compounds, REMn2Ge2 (RE = Ce, Pr, and Nd) magnets, are demonstrated to be able to host skyrmionic bubbles in a wide temperature range of 220–320 K. By further applying a field-cooling procedure, high-density hexagonal lattices of skyrmionic bubbles are realized under zero magnetic field. By combing the micromagnetic simulations, the rotation of easy-magnetized axis plays a dominated role for present REMn2Ge2 magnets, plays a dominated role in the temperature and field induced magnetic domain evolutions. The skyrmionic spin configurations observed in the RE-based magnets can overcome the limiting factors in terms of material variations, operating temperature, and working magnetic field, which is of great significance to practical applications of the skyrmionic spin configurations.

Compositional-driven multiferroic and magnetoelectric properties of NdFeO3-PbTiO3 solid solutions

ABSTRACT Synthesis of polycrystalline (Pb1-x Nd x )(Ti1-x Fe x )O3(for x = 0.21–0.30) solid solutions using solid-state reaction method has been reported. The structural, dielectric, ferroelectric, magnetic, and magnetoelectric properties of the resulting solid solutions have been investigated in detail. The XRD data show that the phase transition occurs at 0.27 ≤ x ≤ 0.28 at room temperature. The dielectric studies show that the transition temperature continuously decreases with increasing “x”. So it is clearly evident from XRD and dielectric data that the tetragonal to cubic phase transition occurs at x = 0.27 to x = 0.28 at room temperature. The remnant polarization (Pr) decreases from 19.78 μC/cm2 to 11.13 µC/cm2 gradually up to x = 0.25 whereas other samples exhibit lossy behavior. The remnant magnetization (Mr) continuously increases from 0.068 emu/g to 0.467 emu/g with composition. All samples exhibit a positive magnetoelectric effect which is the strongest in x = 0.22 sample.

Single crystal growth and structural, magnetic, and magnetoelectric properties in spin-frustrated bow-tie lattice of α-Cu5O2(SeO3)2Cl2

Growth of α-Cu5O2(SeO3)2Cl2 single crystals with unique up-up and down-down ferromagnetic spin-dimers that results in higher magnetoelectric coupling.

Dielectric and magnetoelectric coupling properties of Lead-free (1-x) Bi 0.9Sm 0.1FeO 3/ (x) La 0.7Sr 0.3MnO3 (x = 0, 0.05, 0.1) composites at room temperature

Multiferroic composites (1-x) Bi 0.9Sm 0.1FeO 3/ (x) La 0.7Sr 0.3MnO3 (x = 0, 0.05, 0.1) have been synthesized and their dielectric and magnetoelectric (ME) properties were measured at room temperature. X-ray diffraction patterns show peaks corresponding to both Bi 0.9Sm 0.1FeO 3 (BSFO) and La 0.7Sr 0.3MnO3 (LSMO) phase, which indicates the successful formation of composites. The frequency responses of dielectric properties have been investigated over a wide range of frequencies at room temperature. The dielectric constant and AC conductivity of the samples enhances with increasing content of LSMO. Furthermore, the ME responses of the samples were analyzed at room temperature shows highest ME coupling value of 24.67 mV/cm Oe for composite with x = 0.05. It could generate up to 2.05 V/cm for a magnetic field of 86 Oe. The voltage generation in the composite with modulating AC field maintains a linear relation and point towards the direct application of the material in a variety of next generation low power consuming devices working at room temperature.

Ferroic phase transitions and magnetoelectric coupling in cobalt doped BaTiO3

The ferroelectric and magnetoelectric (ME) properties of cobalt doped BaTiO3 samples.

Magnetoelectric properties of materials based on barium zirconium titanate and various magnetic compounds

Multiferroic composites containing ferroelectric Ba(Ti0.80Zr0.20)O3 (BT80Zr20) phase and magnetic Ni0.7Zn0.3Fe2O4 (NZF), CoFe2O4 (CF) or Ni0.7Cu0.01Sm0.05Zn0.29Fe1.95O4 (NCuSmZF) phase were investigated in this study. Three composites, BT80Zr20-NZF, BT80Zr20-CF and BT80Zr20-NCuSmZF were prepared by mixing chemically synthesized powders in the planetary mill, uniaxial pressing and sintering at 1300?C. X-ray diffraction data for the single phase and composites ceramics indicated the formation of crystallized structure of both ferrites and barium zirconium titanate, without the presence of undesirable phases. Microstructure analysis has shown the formation of two types of nanosized grains, polygonal ferromagnetic andd rounded ferroelectric grains. Non-saturated hysteresis loops were evident in all composite samples possibly due to the presence of very high conductive ferrite phases. The BT80Zr20-CF has shown the lowest conductivity values in comparison with other two compounds and therefore the highest potential for ferroelectric application. The impedance investigations confirmed the presence of different relaxation processes that originate from the grain and grain boundary contributions. Investigation of J-E relation between leakage and electric field for the BT80Zr20 and composites revealed the presence of four possible mechanisms of conduction in these materials.

Investigation of structural, dielectric, and magnetoelectric properties of K0.5Na0.5NbO3–MnFe2O4 lead free composite system

In the present work, lead-free magnetoelectric composites (1 ̶x)K0.5Na0.5NbO3–(x)MnFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) synthesized by solid-state reaction route have been studied for their structural, dielectric, and magnetoelectric properties. The micro-structural analysis (XRD, FESEM, EDX, FTIR, and RAMAN spectroscopy) indicates the coexistence of diphase in the composites. Compared to the individual phases, composites exhibit better electrical properties such as low leakage current, high resistivity, high dielectric constant, and low dielectric loss. I–V characteristics reveal that the conduction behavior of the composites is ohmic in nature in whole tested electric field range at room temperature. The maximum value of dielectric constant is noticed for composite with 20 wt% of MnFe2O4 among the composites. The complex modulus analysis reveals the presence of non-Debye type phenomenon with spreading of relaxation time in the composites. Nyquist plots reveal that the composites exhibit polydispersive Maxwell–Wagner relaxation. The magnetic measurements indicate that the magnetic behavior of the composites lies on the mass content of MnFe2O4 phase. The magnetization increases with MnFe2O4 weight percentage which provides information regarding the magnetoelectric effect (ME) coupling between the magnetostrictive ferromagnetic and ferroelectric phases. Furthermore, ME effect is evaluated as a function of applied magnetic field. The highest ME response of 2.02 mV/cm-Oe is observed for composite with 80 wt% content of MnFe2O4. Findings of this research make these composites worthy material for environment-friendly ME device applications.

Effect of transition metal element substitution on magnetoelectric properties of BiFeO3-BaTiO3 ceramics

BiFeO3 is the most typical multiferroic materials. However, the poor magnetoelectric coupling effect limits its practical application. In this work, the transition metal elements (Co, Mn) were introduced to suppress the spin cycloid structure of BiFeO3-based ceramics. The structure, ferroelectric, magnetic and magnetoelectric properties were investigated thoroughly. The XRD and SAED analysis confirmed the coexistence of tetragonal (T) and rhombohedral (R) phases of all samples. The piezoelectric properties were enhanced in Co-substituted samples. In addition, the magnetic properties were enhanced with the addition of Co/Mn ions. According to the analysis of the M-H loops and XRD patterns before and after poling, the electric-field induced magnetic change was observed in all samples, which can be attributed to the phase transition from R-phase to T-phase during poling. The room-temperature linear magnetoelectric coefficient αME was analyzed, and the maximum αME was obtained at BF-BT-005BC sample, where αME = 0.66 mV/cm Oe. The enhanced magnetic and magnetoelectric properties were ascribed to the distortion of the spiral spin structure by transition metal ions.

Structural Quality and Magnetotransport Properties of Epitaxial Layers of the (Ga,Mn)(Bi,As) Dilute Magnetic Semiconductor.

Structural analysis of epitaxial layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor (DMS), together with investigations of their magnetotransport properties, has been thoroughly performed. The obtained results are compared with those for the reference (Ga,Mn)As layers, grown under similar conditions, with the aim to reveal an impact of Bi incorporation on the properties of this DMS material. Incorporation of Bi into GaAs strongly enhances the spin-orbit coupling strength in this semiconductor, and the same has been expected for the (Ga,Mn)(Bi,As) alloy. In turn, importantly for specific spintronic applications, strong spin-orbit coupling in ferromagnetic systems opens a possibility of directly controlling the direction of magnetization by the electric current. Our investigations, performed with high-resolution X-ray diffractometry and transmission electron microscopy, demonstrate that the (Ga,Mn)(Bi,As) layers of high structural quality and smooth interfaces can be grown by means of the low-temperature molecular-beam epitaxy method, despite a large difference between the sizes of Bi and As atoms. Depending on the applied buffer layer, the DMS layers can be grown under either compressive or tensile misfit strain, which influences their magnetic properties. It is shown that even small 1% Bi content in the layers strongly affects their magnetoelectric properties, such as the coercive field and anisotropic magnetoresistance.

Effect of Nd substitution on magnetoelectric properties of Sm2BaCuO5

We have investigated the magnetic and magnetoelectric properties of solid solutions in the green phase region of the 211-cuprate system Sm2−xNdxBaCuO5 (x = 0.2, 0.4 and 0.6). These compounds crystallize in the centrosymmetric orthorhombic (Pnma) structure. Upon substitution of Nd, the antiferromagnetic ordering temperature of Cu2+ ions (TN1 = 24 K) and Sm3+/Nd3+ ions (TN2 = 5 K) remain unchanged. Dielectric anomalies appear at TN1 under applied magnetic field, whose magnitude increases with field, and at TN2 = 5 K under zero magnetic field for all three compounds. Applied magnetic fields induce electric polarization at TN1 that vary linearly with magnetic fields. While the polarization decreases below TN2 in x = 0 and 0.2, it is enhanced for the samples with x = 0.4 and 0.6. Interestingly, an additional anomaly is observed in dielectric and electric polarization data at 23 K for the composition x = 0.4 under the magnetic fields. Our study reveals that the substitution of Nd significantly modifies the electrical properties due to changes in the interactions between 4f–3d moments.