Yamauchi Kunihiko, Picozzi Silvia
Consiglio Nazionale delle Ricerche-Istituto Nazionale per la Fisica della Materia (CNR-INFM), CASTI Regional Laboratory, 67100 L'Aquila, Italy.
J Phys Condens Matter. 2009 Feb 11;21(6):064203. doi: 10.1088/0953-8984/21/6/064203. Epub 2009 Jan 20.
Improper ferroelectricity in magnets, as induced by non-centrosymmetric spin-, charge- or orbital-ordering, is a branch of the field of multiferroics having fascinating physics and a potentially important technological outcome. We focus here on ferroelectricity in orthorhombic TbMnO(3), where the magnetic field along the a-axis produces a polar collinear spin-arrangement with a rather large in-plane electric polarization. The mechanism, similar to that occurring in orthorhombic HoMnO(3) in the AFM-E phase, is efficiently driven by a large modification of the structural properties (such as MnO bond-lengths and Mn-O-Mn bond-angles) to favor e(g) electron hopping between Mn with parallel spins. A similar mechanism where the t(2g) states are involved is examined through a hypothetical collinear spin-structure, resulting in a weaker out-of-plane ferroelectric polarization.
由非中心对称自旋、电荷或轨道有序诱导产生的磁体中的反常铁电性，是多铁性领域的一个分支，具有引人入胜的物理学特性和潜在的重要技术成果。我们在此聚焦于正交晶系TbMnO₃中的铁电性，其中沿a轴的磁场会产生具有相当大的面内极化的极性共线自旋排列。该机制类似于在AFM - E相的正交晶系HoMnO₃中发生的机制，通过结构性质（如MnO键长和Mn - O - Mn键角）的大幅改变有效地驱动，以利于具有平行自旋的Mn之间的e(g)电子跳跃。通过假设的共线自旋结构研究了涉及t(2g)态的类似机制，结果导致较弱的面外铁电极化。
