Proceedings PaperTheoretical study of magnetic semiconductors with high Curie temperatures (Conference Presentation)
Combining magnetism and semiconductor enables the development of magnetic semiconductors, a promising way to realize spintronic applications based on use of both charge and spin degrees of freedom. The highest Curie temperature of the most extensively studied diluted magnetic semiconductor (DMS) (Ga,Mn)As has been Tc = 200 K, still far below room temperature. Owing to simultaneous doping of charge and spin induced by Mn substitution, it is difficult to individually optimize charge and spin densities. To overcome these difficulties, recently a new type of DMS (Ba,K)(Zn,Mn)2As2 was observed in experiments with Tc up to 230K . Motivated by the high Tc, density functional theory calculations  and photoemission spectroscopy experiments  were conducted to understand the microscopic mechanism of ferromagnetism of p-type DMS (Ba,K)(Zn,Mn)2As2. In addition, the n-type DMS Ba(Zn,Mn,Co)2As2 was also reported in the recent experiments with Tc = 45 K. In Mn-doped BaZn2As2, why is the ferromagnetic coupling? Why is Tc much lower in the n-type case than that in p-type case? In general, can p- and n-type DMS be realized? Here, we propose a method to realize DMS with p- and n-type carriers by choosing host semiconductors with a narrow band gap [5, 6]. By density function theory and quantum Monte Carlo simulation, we demonstrate such semiconductors using Mn-doped BaZn2As2, which has a band gap of 0.2 eV. In addition, we found a new non-toxic DMS Mn-doped BaZn2Sb2, of which the Curie temperature Tc is predicted to be higher than that of Mn-doped BaZn2As2, the Tc of which was up to 230 K in the recent experiment . We also predict the DMS Cr-doped BaZn2As2 with stable ferromagnetism in p- and n-type carriers . In addition, by density functional theory calculations we predict the strain-induced room-temperature intrinsic ferromagnetic semiconductors in two-dimensional Cr2Ge2Se6 . We find that Tc = 144 K in Cr2Ge2Se6, which can be enhanced to Tc = 326 K by applying 3% strain, and Tc = 421 K by 5% strain. The enhanced Tc in Cr2Ge2Se6 by strain can be understood by superexchange interaction. References:  K. Zhao et al., Nat. Commun. 4, 1442 (2013); Chin. Sci. Bull. 59, 2524 (2014).  J. K. Glasbrenner, I. Zutic, and I. I. Mazin, Phys. Rev. B 90, 140403(R) (2014).  H. Suzuki et al., Phys. Rev. B 91, 140401(R) (2015); Phys. Rev. B 92, 235120 (2015).  H. Y. Man et al., arXiv:1403.4019 (2014); S. Guo et al., arXiv:1712.06764 (2017).  B. Gu, and S. Maekawa, Phys. Rev. B 94, 155202 (2016).  B. Gu, and S. Maekawa, AIP Advances 7, 055805 (2017).  X. J. Dong, J. Y. You, B. Gu, and G. Su, arXiv:1901.09306 (2019).