Exchange Interactions and Curie Temperatures in Dilute Magnetic Semiconductors
Exchange Interactions and Curie Temperatures in Dilute Magnetic Semiconductors
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DOI：
10.1007/s10751-005-9149-5
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发表时间：
2004-03
影响因子：
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通讯作者：
Kazunori Sato;Kazunori Sato;P. Dederichs;H. Katayama‐Yoshida
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作者：
Kazunori Sato;Kazunori Sato;P. Dederichs;H. Katayama‐Yoshida
我们讨论了稀磁半导体铁磁性的起源基于从头计算Mn掺杂的GaN，GaP，GaAs和GaSb。我们使用Korringa-Kohn-Rostoker方法结合相干势近似来描述替代和矩无序。居里温度（TC）的计算从第一原理通过使用海森堡模型在平均场近似的映射。发现如果在差距中形成杂质带，如（Ga，Mn）N的情况，则双交换占主导地位，导致TC作为Mn浓度c的函数的特征性ε c依赖性。另一方面，如果d态是局域的，如在（Ga，Mn）Sb中，则Zener的p-d交换占优势，导致TC的线性依赖性。为了更精确地估计TC，用Reynstensteinet公式计算了有效交换耦合常数Jij，发现（Ga，Mn）N中的交换作用范围很短。另一方面，在（Ga，Mn）As的相互作用是弱的，但长程。Monte Carlo模拟表明，（Ga，Mn）N的TC值很低，因为在低浓度下难以实现渗流，平均场近似大大高估了TC。即使在（Ga，Mn）As中，渗流效应仍然很重要.
We discuss the origin of ferromagnetism in dilute magnetic semiconductors based on ab initio calculations for Mn-doped GaN, GaP, GaAs and GaSb. We use the Korringa–Kohn–Rostoker method in connection with the coherent potential approximation to describe the substitutional and moment disorder. Curie temperatures (TC) are calculated from first-principles by using a mapping on a Heisenberg model in a mean field approximation. It is found that if impurity bands are formed in the gap, as it is the case for (Ga, Mn)N, double exchange dominates leading to a characteristic √cdependence ofTCas a function of the Mn concentrationc. On the other hand, if the d-states are localized, as in (Ga, Mn)Sb, Zener's p–d exchange prevails resulting in a linearc-dependence ofTC. In order to have more precise estimations ofTC, effective exchange coupling constantsJij's are calculated by using the formula of Liechtensteinet al.It is found that the range of the exchange interaction in (Ga, Mn)N is very short. On the other hand, in (Ga, Mn)As the interaction is weaker but long ranged. Monte Carlo simulations show that theTCvalues of (Ga, Mn)N are very low since percolation is difficult to achieve for small concentrations and the mean field approximation strongly overestimatesTC. Even in (Ga, Mn)As the percolation effect is still important.