铕单硫族化物磁性半导体中的交换相互作用及其对流体静力应变的依赖性
Exchange interactions in europium monochalcogenide magnetic semiconductors and their dependence on hydrostatic strain
摘要：
采用经典的Heisenberg模型，用Monte Carlo方法研究了EuO，EuS，EuSe和EuTe中的间接最近邻（NN）交换和次最近邻（NNN）超交换相互作用的距离依赖性.为此，首先，磁有序温度的依赖性，即，居里，分别确定了铁磁和反铁磁有序交换常数的Néel温度。然后，这是用于分析的实验数据的静水压力实验。它表明，所有的实验结果，即，随着晶格常数的减小，EuTe和EuSe的临界温度的急剧升高以及从反铁磁有序向铁磁有序的转变可以用磁Grüneisen定律很好地描述，其中交换常数以幂律的形式依赖于Eu离子的原子间距离.根据这些计算，对于所有四种铕单硫族化物，间接NN交换的特征在于约20的Grüneisen指数和约10的NNN超交换指数。后者同意Bloch的经验10/3定律的超交换相互作用的绝缘磁性材料的体积依赖性。蒙特卡罗计算也产生显着修订的交换常数为无应变的散装材料，因为自旋波动在非零温度考虑在内。随着晶格参数的减小，交换常数的强烈增加为应变外延结构中居里温度的增加提供了空间，这对于器件应用是重要的。
英文摘要：
The classical Heisenberg model is applied in a Monte Carlo study to investigate the distance dependence of the indirect nearest neighbor (NN) exchange and next-nearest neighbor (NNN) superexchange interaction in EuO, EuS, EuSe and EuTe. For this purpose, first, the dependence of the magnetic ordering temperature, i.e., Curie, respectively, Néel temperature for ferromagnetic and antiferromagnetic ordering on the exchange constants was determined. This was then employed for the analysis of experimental data of hydrostatic pressure experiments. It is shown that all experimental findings, i.e., the strong increase of the critical temperatures, as well as the transition from antiferromagnetic to ferromagnetic ordering for EuTe and EuSe with decreasing lattice parameter is well described by the magnetic Grüneisen law, in which the exchange constants depend on the interatomic distances of the Eu ions in the form of a power law. According to these calculations, the indirect NN exchange is characterized by a Grüneisen exponent of approximately 20 and the NNN superexchange by an exponent of about 10 for all four europium monochalcogenides. The latter agrees with Bloch's empirical 10/3 law for the volume dependence of superexchange interactions in insulating magnetic materials. The Monte Carlo calculations also yield significantly revised exchange constants for unstrained bulk material because spin fluctuations at non-zero temperatures are taken into account. The strong increase of the exchange constants with decreasing lattice parameter provides room for increasing the Curie temperatures in strained epitaxial structures, which is important for device applications.
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