Exchange couplings for Mn ions in CdTe: Validity of spin models for dilute magnetic II-VI semiconductors
Exchange couplings for Mn ions in CdTe: Validity of spin models for dilute magnetic II-VI semiconductors
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CdTe 中 Mn 离子的交换耦合：稀磁 II-VI 半导体自旋模型的有效性
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
F. Anders
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文献类型：
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作者：
Thorben Linneweber;Jorg Bunemann;Ute Low;F. Gebhard;F. Anders
我们采用密度泛函理论（DFT）的广义梯度近似（GGA）及其扩展GGA+$U$和GGA+Gutzwiller计算Mn离子对之间的磁交换耦合取代镉在CdTe晶体中在很小的掺杂。DFT（GGA）高估了三倍的交换耦合，因为它低估了Mn掺杂的II-VI族半导体中的电荷转移间隙。在GGA+ U$、GGA+Gutzwiller或DFT（GGA）结果的简单标度下，将最近邻耦合J_1 $固定到其实验值，可提供Cd（Mn）Te、Zn（Mn）Te、Zn（Mn）Se和Zn（Mn）S中第二、第三和第四邻距离处交换耦合的可接受值。特别地，我们恢复了实验上观察到的关系$J_4> J_2，J_3 $。Mn 3$d$-壳层的填充不是整数，这使得潜在的海森堡描述受到质疑。然而，使用一个少离子玩具模型的图片出现了一个稍微扩展的本地时刻，使一个整数$3d$-壳填充是不是一个先决条件等距磁化高原，如在实验中所看到的。
We employ density-functional theory (DFT) in the generalized gradient approximation (GGA) and its extensions GGA+$U$ and GGA+Gutzwiller to calculate the magnetic exchange couplings between pairs of Mn ions substituting Cd in a CdTe crystal at very small doping. DFT(GGA) overestimates the exchange couplings by a factor of three because it underestimates the charge-transfer gap in Mn-doped II-VI semiconductors. Fixing the nearest-neighbor coupling $J_1$ to its experimental value in GGA+$U$, in GGA+Gutzwiller, or by a simple scaling of the DFT(GGA) results provides acceptable values for the exchange couplings at 2nd, 3rd, and 4th neighbor distances in Cd(Mn)Te, Zn(Mn)Te, Zn(Mn)Se, and Zn(Mn)S. In particular, we recover the experimentally observed relation $J_4>J_2,J_3$. The filling of the Mn 3$d$-shell is not integer which puts the underlying Heisenberg description into question. However, using a few-ion toy model the picture of a slightly extended local moment emerges so that an integer $3d$-shell filling is not a prerequisite for equidistant magnetization plateaus, as seen in experiment.