Intrinsic Magnetoelectric Effect Research Articles

Quantum theory of the intrinsic orbital magnetoelectric effect in itinerant electron systems at finite temperatures

Magnetization can be induced by an electric field in systems without inversion symmetry $\mathcal{P}$ and time-reversal symmetry $\mathcal{T}$. This phenomenon is called the magnetoelectric (ME) effect. The spin ME effect has been actively studied in multiferroics. The orbital ME effect also exists and has been mainly discussed in topological insulators at zero temperature. In this paper, we study the intrinsic orbital ME response in metals at finite temperature using the Kubo formula. The intrinsic response originates from the Fermi sea and does not depend on the dissipation. Especially in systems with $\mathcal{PT}$ symmetry, the extrinsic orbital ME effect becomes zero, and the intrinsic ME effect is dominant. We apply the response tensor obtained in this work to a $\mathcal{PT}$-symmetric model Hamiltonian with antiferromagnetic loop current order, demonstrating that the intrinsic ME effect is enhanced around the Dirac points.

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.

Magnetoelectric effect in Sm-substituted tungsten bronze structure Ba4(SmxLa1-x)2Fe2Nb8O30 ceramics

Magnetoelectric effect is directly measured in the Ba4(SmxLa1-x)2Fe2Nb8O30 ceramics, which is rarely reported in tungsten bronze ceramics. Besides, the effects of Sm-substitution on the crystal structure, dielectric, ferroelectric and magnetic properties have been systematically studied. XRD Rietveld refinement confirms all the ceramics to be single phase with space group of P4bm. With the increase of x, Ba4(SmxLa1-x)2Fe2Nb8O30 ceramics transform from paraelectric to ferroelectric. The compositions of x = 0.9, 0.95 and 1 show first-order ferroelectric phase transitions above room temperature. Compared to composition x = 0, the dielectric constant of other compositions exhibits frequency stability and the dielectric loss decreases apparently at room temperature. The ferroelectricity improves with increasing x, which can be ascribed to the increased A2-A1 ionic radius difference. Meanwhile, the magnetic hysteresis loops are obtained for some compositions. All the results approve Ba4(SmxLa1-x)2Fe2Nb8O30 (x = 0.9, 0.95, 1) ceramics as room temperature multiferroic materials with intrinsic magnetoelectric effect.

Temperature and field induced spin reorientation and dielectric properties in YCr0.88Fe0.12O3 single crystal

The structural, magnetic, and dielectric properties of the YCr0.88Fe0.12O3 single crystals were studied. Detailed magnetic studies demonstrate that the crystal is antiferromagnetic with weak canted ferromagnetism and experiences three sequential magnetic transitions around TN1 ∼ 127.3 K, TN2 ∼ 115.2 K, and TSR ∼ 99.0 K. Interestingly, a temperature induced spin reorientation (SR) near TSR and magnetic field induced SR below TSR were observed. The H–T phase diagram was revealed to be quite different from both parent compounds YFeO3 and YCrO3. A dielectric relaxation around TN1 was found to be associated with electron hopping. An intrinsic magnetoelectric effect was also observed at low temperatures. These results are helpful for understanding the exotic magnetic and magnetoelectric properties in the orthochromite and orthoferrite related systems.

Nonlinear magnetoelectric effect and magnetostriction in piezoelectric CsCuCl3 in paramagnetic and antiferromagnetic states

The direct nonlinear magnetoelectric (ME) effect and the magnetostriction of piezoelectric CsCuCl3 single crystals were comprehensively studied over a wide temperature range in stationary magnetic fields of up to 14 T. The direct nonlinear ME effect measurements were also performed in pulsed magnetic fields up to 31 T, at liquid helium temperature in the antiferromagnetic (AF) state for the crystallographic direction in which effect has the maximum value. The nonlinear ME effect was quadratic in the paramagnetic state for the whole range of magnetic fields. In the AF state the phase transition between different configurations of spins manifested itself as plateau-like peculiarity on the nonlinear ME effect. The nonlinear ME effect was saturated by the phase transition to the spin-saturated paramagnetic state. Two contributions to the nonlinear ME effects in CsCuCl3 were extracted from the experimental data: the intrinsic ME effect originated from the magnetoelectric interactions, and the extrinsic one, which resulted from a magnetostriction-induced piezoelectric effect.

Nanoscale-driven crystal growth of hexaferrite heterostructures for magnetoelectric tuning of microwave semiconductor integrated devices.

A nanoscale-driven crystal growth of magnetic hexaferrites was successfully demonstrated at low growth temperatures (25-40% lower than the temperatures required often for crystal growth). This outcome exhibits thermodynamic processes of crystal growth, allowing ease in fabrication of advanced multifunctional materials. Most importantly, the crystal growth technique is considered theoretically and experimentally to be universal and suitable for the growth of a wide range of diverse crystals. In the present experiment, the conical spin structure of Co2Y ferrite crystals was found to give rise to an intrinsic magnetoelectric effect. Our experiment reveals a remarkable increase in the conical phase transition temperature by ∼150 K for Co2Y ferrite, compared to 5-10 K of Zn2Y ferrites recently reported. The high quality Co2Y ferrite crystals, having low microwave loss and magnetoelectricity, were successfully grown on a wide bandgap semiconductor GaN. The demonstration of the nanostructure materials-based "system on a wafer" architecture is a critical milestone to next generation microwave integrated systems. It is also practical that future microwave integrated systems and their magnetic performances could be tuned by an electric field because of the magnetoelectricity of hexaferrites.

Ferromagnetic-nonmagnetic and metal-insulator phase transitions at the interfaces of KTaO3 and PbTiO3

We studied the electronic and magnetic properties of hole doped KTaO3/PbTiO3 interface using density functional theory methods. Ferromagnetic-nonmagnetic phase transition and metal-insulator phase transition occur simultaneously at the interface with ferroelectric polarization reversal. Furthermore, these two transitions are coupled with each other because hole doping with large concentration of holes gives rise to ferromagnetism. The interfacial magnetization, which is proportional to hole concentration at the interface, can be tuned by ferroelectric polarization, leading to strong intrinsic magnetoelectric effect at the interface of originally nonmagnetic KTaO3 and PbTiO3.

Two-step transition in a magnetoelectric ferrimagnet Cu2OSeO3

We report a detailed single-crystal investigation of a magnetoelectric ferrimagnet ${\mathrm{Cu}}_{2}{\mathrm{OSeO}}_{3}$ using dc magnetization and ac susceptibility along the three principal directions [100], [110], and [111]. We have observed that in small magnetic fields two magnetic transitions occur, one at ${T}_{c}=57$ K and the second one at ${T}_{N}=58$ K. At ${T}_{c}$ the nonlinear susceptibility reveals the emergence of the ferromagnetic component and below ${T}_{c}$ the magnetization measurements show the splitting between field-cooled and zero-field-cooled regimes. Above 1000 Oe the magnetization saturates and the system is in a single domain state. The temperature dependence of the saturation below ${T}_{c}$ can be well described by $\ensuremath{\mu}(T)=\ensuremath{\mu}(0){[1\ensuremath{-}{(T/{T}_{c})}^{2}]}^{\ensuremath{\beta}}$, with $\ensuremath{\mu}(0)=0.56{\ensuremath{\mu}}_{B}$/Cu, corresponding to the 3-up-1-down configuration. The dielectric constant measured on a thin single crystal shows a systematic deviation below the transition, indicating an intrinsic magnetoelectric effect.