Biquadratic exchange interactions in two-dimensional magnets
Biquadratic exchange interactions in two-dimensional magnets
复制标题
二维磁体中的双二次交换相互作用
DOI：
10.1038/s41524-020-00416-1
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发表时间：
2020-10-09
影响因子：
9.7
通讯作者：
Santos, Elton J. G.
中科院分区：
文献类型：
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作者：
Kartsev, Alexey;Augustin, Mathias;Santos, Elton J. G.
最近发现的货车范德华材料的磁性为研究真正二维的基本自旋相互作用开辟了几条途径。一个首要的问题是，双线性海森堡交换之外的高阶相互作用对少原子厚化合物的磁性有什么影响。在这里，我们证明了双二次交换相互作用，这是最简单和最自然的形式的非海森堡耦合，假设层状磁体的磁性能的关键作用。结合使用非微扰分析技术，非共线的第一原理方法和经典的蒙特卡罗计算，将高阶交换，我们表明，几个数量，包括磁各向异性，自旋波隙和拓扑自旋激发本质上重整化导致进一步的热稳定性的层。我们开发了一个自旋哈密顿量，也包含反对称交换（例如，Dzyaloshinskiii-Moriya相互作用）成功地合理化了许多观察结果，例如尽管有很强的磁各向异性，但几种化合物的非伊辛特性，二维磁体的磁振子谱的特殊性，以及测量和计算的居里温度之间的差异。我们的研究结果提供了一个理论框架，探索不同的物理现象，在二维磁体中，双二次交换相互作用有重要的贡献。
Magnetism in recently discovered van der Waals materials has opened several avenues in the study of fundamental spin interactions in truly two-dimensions. A paramount question is what effect higher-order interactions beyond bilinear Heisenberg exchange have on the magnetic properties of few-atom thick compounds. Here we demonstrate that biquadratic exchange interactions, which is the simplest and most natural form of non-Heisenberg coupling, assume a key role in the magnetic properties of layered magnets. Using a combination of nonperturbative analytical techniques, non-collinear first-principles methods and classical Monte Carlo calculations that incorporate higher-order exchange, we show that several quantities including magnetic anisotropies, spin-wave gaps and topological spin-excitations are intrinsically renormalized leading to further thermal stability of the layers. We develop a spin Hamiltonian that also contains antisymmetric exchanges (e.g., Dzyaloshinskii-Moriya interactions) to successfully rationalize numerous observations, such as the non-Ising character of several compounds despite a strong magnetic anisotropy, peculiarities of the magnon spectrum of 2D magnets, and the discrepancy between measured and calculated Curie temperatures. Our results provide a theoretical framework for the exploration of different physical phenomena in 2D magnets where biquadratic exchange interactions have an important contribution.