Multiferroic State Research Articles

Density-functional analysis of spin exchange and ferroelectric polarization inAgCrO2

Density-functional calculations were carried out for AgCrO2 to examine its spin exchange and ferroelectric polarization. In the multiferroic state of AgCrO2 the triangular spin lattice of each CrO2 layer forms parallel chains with helical-spin order. The spin exchange interactions of AgCrO2 are strongly frustrated both within and between adjacent CuO2 layers, which gives rise to the observed helical-spin order. The observed ferroelectric polarization of AgCrO2 is not caused by individual helical-spin chains, but by the spiral-spin chain structures that propagate between the helical-spin chains.

Electrical control of magnetization in charge-ordered multiferroicLuFe2O4

${\text{LuFe}}_{2}{\text{O}}_{4}$ exhibits multiferroicity due to charge order on a frustrated triangular lattice. We find that the magnetization of ${\text{LuFe}}_{2}{\text{O}}_{4}$ in the multiferroic state can be electrically controlled by applying voltage pulses. Depending on with or without magnetic fields, the magnetization can be electrically switched up or down. We have excluded thermal heating effect and attributed this electrical control of magnetization to an intrinsic magnetoelectric coupling in response to the electrical breakdown of charge ordering. Our findings open up an effective way toward electrical control of magnetization.

Nonlinear optical detection of a ferromagnetic state at the single interface of an antiferromagneticLaMnO3/SrMnO3double layer

Emergence of a ferromagnetic state at the single interface of two antiferromagnetic perovskite manganites, ${\text{LaMnO}}_{3}$ and ${\text{SrMnO}}_{3}$, has been detected with nonlinear magneto-optical Kerr rotation. The samples are composed of approximately four unit cells of each material, with reversed stacking sequence. The existence and orientations of the interface dipole or that of so-called toroidal moment were determined through phase-sensitive second-harmonic detection. Characterization of multiferroic states at the single interfaces, and non-negligible effect of surfaces on the Kerr rotation are demonstrated.

다중강전자 상태를 가진 육방정계물질의 전자구조 계산

다중강전자 상태의 <TEX>$YMnO_3,\;ScMnO_3$</TEX>의 전자구조와 자기구조를 국소스핀밀도근사(LSDA)를 이용하여 계산하였다. 강자성 상태이며 강유전 상태의 전자구조는 육방정계 구조로 인하여 Mn 3d 에너지띠가 분리되어 띠틈을 나타내었다. 이러한 에너지 띠틈과 작은 Y, Sc 이온의 반경으로 인하여 <TEX>$YMnO_3,\;ScMnO_3$</TEX>는 반강자성 강유전적 성질을 가지는 다중강전자 구조를 가지고 있음을 보았다. 또한 총에너지 계산을 통하여 반강자성, 강유전 상태가 가장 안정됨이 실험과 일치하였다. We have studied electronic structures and magnetic properties of <TEX>$YMnO_3,\;ScManO_3$</TEX> with hexagonal structure using Full Potential Linearized Augmented Plane Wave (FLAPW) method based on LSDA method. LSDA calculation results show that multiferroic <TEX>$YMnO_3$</TEX> shows energy gap due to hexagonal symmetry and magnetic interaction. Because of insulating gap and small Y ion, <TEX>$YMnO_3$</TEX> shows magnetic and ferroelectric state. However, <TEX>$ScMnO_3$</TEX> does not show the energy gap because of strong hybridization of Mn-O for LSDA calculation. We confirmed the stability of multiferroic state for <TEX>$YMnO_3\;and\;ScManO_3$</TEX> using total energy calculations. The antiferromagnetic and ferroelectric states have the lowest energy about 100 meV.

New orthorhombic multiferroics R1–xYx MnO3 (R = Eu, Gd)

AbstractA tendency to form multiferroic states with a spatially modulated antiferromagnetic structure and electric polarization in pure orthorhombic manganites RMnO3 upon decreasing of the rare‐earth ionic radii has been realized in single crystals of substituted compounds Eu1–x Yx MnO3 (0.2 ≤ x ≤ 0.5) and Gd1–y Yy MnO3 (0 ≤ y ≤ 0.2). While the parent pure and slightly substituted (x ≤ 0.1) compounds exhibited a spontaneous transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at T CA &lt; T N = 45–50 K, the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at T lock &lt; T N for x ≥ 0.3 and y ≥ 0.05 accompanied by dielectric anomalies. Various phase transitions were observed in magnetic fields up to 250 kOe along the a ‐, b ‐, c ‐axes by magnetization, magnetostriction and electric polarization measurements. The latter indicate the existence of a spontaneous electric polarization below T lock. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Magnetic, dielectric and magnetoelectric properties of new family of orthorhombic multiferroic Eu 1−xY xMNO 3 manganites

Multiferroic ground states with a spatially modulated antiferromagnetic structure and electric polarization have been revealed in Eu 1− x Y x MnO 3 ( 0.2 ⩽ x ⩽ 0.5 ) single crystals. While the slightly substituted ( x ⩽ 0.1 ) compounds exhibited a transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at T CA < T N , the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at T lock < T N for x > 0.2 . Various phase transitions were observed in the magnetic fields up to 250 kOe along a, b, c axes by magnetization, magnetostriction and electric polarization measurements which show an existence of a spontaneous electric polarization below T lock.