In the mid 1990's Hideo Ohno and co-workers succeeded in substituting Mn into Ga site of a III-V semiconductor GaAs by using Molecular Beam Epitaxy (MBE), opening a field of diluted magnetic semiconductors (DMS).  Since then, ferromagnetic (Ga,Mn)As has been extensively studied with respect to possible applications to spin sensitive electronics (spintronics) devices.  Substitution of Mn^{2+} and Ga^{3+}, however, led to limitations as (a) very small chemical solubility which prohibits availability of bulk specimens; and (b) simultaneous spin and charge doping leading only to p-type systems.

Collaborative effort by the group of Chanqing Jin (IOP) and the present speaker has succeeded in synthesizing new DMS systems Li(Zn,Mn)As ([1] ferromagnetic Tc up to 50 K) and (Ba,K)(Zn,Mn)2As2 ([2] Tc up to 200 K). These systems have similar/identical crystal structures with those of FeAs superconductors LiFeAs and (Ba,K)Fe2As2, with a very good matching of lattice parameters.  Bulk specimens of these new DMS systms have already enabled NMR and neutron measurements, while future developments may allow production of n-type ferromagnets, bipolar transistors, and multilayer/interface junctions of various combinations of lattice-matched semiconductor, ferromagnet, antiferromagnet and superconductor.

In this talk, I will describe our materials developments and MuSR studies on these traditional [3] and novel [1,2] DMS systems. If time allows, I will also cover our MuSR results on "topological superconductors", including time reversal symmetry breaking of Sr2RuO4 [4], static magnetic order of (Sr,Ca)2RuO4 [5] and most recent findings on bulk specimen of Cu0.3Bi2Se3.[6].

[1] D. Zheng et al. Nature Communications, 2:422 (2011)
[2] K. Zhao et al., Nacure Communications, to be published.
[3] S.R. Dunsiger et al., Nature Materials, 9, 299-303 (2010).
[4] G.M. Luke et al., Nature 394 (1998) 558.
[5] J.P. Carlo et al., Nature Materials 11 (2012) 323.
[6] Unpublished work performed in collaboration with Yoichi Ando.

[1,2] have been performed with C.Q. Jin, F.L. Ning, Yayu Wang, S. Maekawa, Bo Gu, S.R. Dunsiger, W. Higemoto, T. Goko and others with support from JAEA, REIMEI project and NSF Super-PIRE Collaboration.