First-principles calculation of filled tetrahedral compound magnetic semiconductors

Kazunori Sato

Osaka University, Graduate School of Engineering Science, Osaka, Japan

To realize semiconductor spintronics, much effort has been devoted to synthesize dilute magnetic semiconductors (DMS) with room-temperature ferromagnetism. According to the first-principles calculations [1] the magnetic percolation effect is disastrous to the high temperature ferromagnetism in DMS in particular for low concentration. Thus, to realize high-TC it is important to find a way to dope magnetic impurities into host semiconductors up to high concentration. So far, the Mn-doped III-V compound based semiconductors have been investigated as promising spintronics materials. For example, in case of (Ga, Mn)As we substitute Mn2+ for Ga3+, thus the system becomes p-type and introduced hole carriers mediate ferromagnetic interactions (i.e., carrier induced ferromagnetism). However, high concentration doping of Mn is always tricky in these systems.

In this work, we propose filled tetrahedral compounds, such as LiZnAs, LiZnP and LiZnN, as host materials of magnetic semiconductors. The crystal structure of LiZnAs shows zinc-blende framework of ZnAs and its tetrahedral interstitial sites surrounded by As are filled up by Li completely. In this case, Mn2+ ions occupy Zn2+ sites, thus we can expect rather high solubility of Mn in these compounds [2]. Our calculations are based on the local density approximation and we use the Korringa-Kohn-Rostoker coherent potential approximation method [3] to simulate substitutional disorder in the material. It is found that by introducing Li vacancies in, e.g. Li(Zn, Mn)As, the system becomes p-type and the ferromagnetism appears. The calculated density of states suggests that the p-d exchange mediates the ferromagnetic interaction between Mn. Since the removal of Li is expected to be rather easy, we can induce the ferromagnetism in Li(Zn, Mn)As by using post-growth annealing. For estimating Curie temperature we use the mean field approximation, random phase approximation and Monte Carlo simulation. Systematic study on the magnetism of filled tetrahedral compound based DMS will be discussed in the presentation.

References:
1. K. Sato et al., Rev. Mod. Phys. 82, 1633 (2010).
2. J. Masek et al. Phys. Rev. Lett. 98, 067202 (2007).
3. MACHIKANEYAMA2002 developed by Akai, http://kkr.phys.sci.osaka-u.ac.jp

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