Logemann R, Rudenko A N, Katsnelson M I, Kirilyuk A
Radboud University, Institute for Molecules and Materials, NL-6525 AJ Nijmegen, Netherlands.
J Phys Condens Matter. 2017 Aug 23;29(33):335801. doi: 10.1088/1361-648X/aa7b00. Epub 2017 Jun 22.
Magnetism of transition metal (TM) oxides is usually described in terms of the Heisenberg model, with orientation-independent interactions between the spins. However, the applicability of such a model is not fully justified for TM oxides because spin polarization of oxygen is usually ignored. In the conventional model based on the Anderson principle, oxygen effects are considered as a property of the TM ion and only TM interactions are relevant. Here, we perform a systematic comparison between two approaches for spin polarization on oxygen in typical TM oxides. To this end, we calculate the exchange interactions in NiO, MnO and hematite (FeO) for different magnetic configurations using the magnetic force theorem. We consider the full spin Hamiltonian including oxygen sites, and also derive an effective model where the spin polarization on oxygen renormalizes the exchange interactions between TM sites. Surprisingly, the exchange interactions in NiO depend on the magnetic state if spin polarization on oxygen is neglected, resulting in non-Heisenberg behavior. In contrast, the inclusion of spin polarization in NiO makes the Heisenberg model more applicable. Just the opposite, MnO behaves as a Heisenberg magnet when oxygen spin polarization is neglected, but shows strong non-Heisenberg effects when spin polarization on oxygen is included. In hematite, both models result in non-Heisenberg behavior. The general applicability of the magnetic force theorem as well as the Heisenberg model to TM oxides is discussed.
过渡金属（TM）氧化物的磁性通常用海森堡模型来描述，其中自旋之间的相互作用与取向无关。然而，这种模型对TM氧化物的适用性并不完全合理，因为通常忽略了氧的自旋极化。在基于安德森原理的传统模型中，氧的效应被视为TM离子的一种属性，只有TM之间的相互作用才是相关的。在这里，我们对典型TM氧化物中氧的两种自旋极化方法进行了系统比较。为此，我们使用磁力定理计算了NiO、MnO和赤铁矿（FeO）在不同磁构型下的交换相互作用。我们考虑了包含氧位点的完整自旋哈密顿量，还推导了一个有效模型，其中氧上的自旋极化使TM位点之间的交换相互作用重整化。令人惊讶的是，如果忽略氧上的自旋极化，NiO中的交换相互作用取决于磁状态，导致非海森堡行为。相反，在NiO中考虑自旋极化使海森堡模型更适用。恰恰相反，当忽略氧自旋极化时，MnO表现为海森堡磁体，但当考虑氧上的自旋极化时，会表现出强烈的非海森堡效应。在赤铁矿中，两种模型都导致非海森堡行为。我们讨论了磁力定理以及海森堡模型对TM氧化物的一般适用性。
