Low-temperature ferromagnetism in (Ga, Mn)N: Ab initio calculations
Low-temperature ferromagnetism in (Ga, Mn)N: Ab initio calculations
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DOI：
10.1103/physrevb.70.201202
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发表时间：
2004-11
影响因子：
3.7
通讯作者：
Kazunori Sato;W. Schweika;P. Dederichs;H. Katayama‐Yoshida
中科院分区：
文献类型：
--
作者：
Kazunori Sato;W. Schweika;P. Dederichs;H. Katayama‐Yoshida
通过将从头算结果映射到经典海森堡模型上，从第一性原理计算了稀磁半导体（DMS）的磁性。在局域密度近似下，采用Korringa-Kohn-Rostoker相干势近似（KKR-CPA）方法计算了（Ga，Mn）N和（Ga，Mn）As的电子结构.通过在CPA介质中的i和j位嵌入两种Mn杂质并使用Liattensteinet等人的Jij公式[J.Magn.Magn.Mater.67，65（1987）]来确定有效交换耦合常数Jij ′。发现（Ga，Mn）N中的交换作用范围很短，主要是双交换机制，这是由于杂质波函数在差距中呈指数衰减的缘故。另一方面，在p-d交换机制占主导地位的（Ga，Mn）As中，相互作用范围较弱但范围较长，因为扩展价空穴态介导了铁磁相互作用。本文采用平均场近似、随机相位近似和MonteCarlo方法计算了直磁半导体的居里温度。据发现，TC值的（Ga，Mn）N是非常低的，因为，由于短程相互作用，渗滤的铁磁耦合是难以实现的小浓度。MFA严重高估了TC。即使在（Ga，Mn）As中，交换作用范围更长，渗滤效应仍然很重要，MFA高估TC约50%-100%。
The magnetic properties of dilute magnetic semiconductors (DMSs) are calculated from first-principles by mapping theab initio results on a classical Heisenberg model. By using the Korringa–Kohn–Rostoker coherent-potential approximation (KKR-CPA) method within the local-density approximation, the electronic structure of(Ga, Mn)N and (Ga, Mn)As is calculated. Effective exchange coupling constants Jij ’ are determined by embedding two Mn impurities at sites i and j in the CPA medium and using the Jij formula of Liechtensteinet al. [J. Magn. Magn. Mater.67, 65 (1987)]. It is found that the range of the exchange interaction in(Ga, Mn)N, being dominated by the double exchange mechanism, is very short ranged due to the exponential decay of the impurity wave function in the gap. On the other hand, in (Ga, Mn)As, wherep-d exchange mechanism dominates, the interaction range is weaker but long ranged, because the extended valence hole states mediate the ferromagnetic interaction. Curie temperatures (TC’s) of DMSs are calculated by using the mean-field approximation (MFA), the random-phase approximation, and the, in principle exact, Monte Carlo method. It is found that the TC values of (Ga, Mn)N are very low since, due to the short-ranged interaction, percolation of the ferromagnetic coupling is difficult to achieve for small concentrations. The MFA strongly overestimates TC. Even in(Ga, Mn)As, where the exchange interaction is longer ranged, the percolation effect is still important and the MFA overestimates TC by about 50%–100%.