Manipulation of nuclear spins in GaAs using a half-metallic spin source of Co<inf>2</inf>MnSi

Abstract

Nuclear spins in semiconductors are an ideal system for implementing quantum bits (qubits) for quantum computation because of an extremely long coherence time. Dynamic nuclear polarization (DNP) through hyperfine interaction with electron spins and control of nuclear spin states by nuclear magnetic resonance (NMR) in semiconductors provide basic technologies for implementing nuclear-spin based qubits. A half-metallic ferromagnet could be considered an excellent candidate for a spin source for efficient DNP because it provides complete spin polarization at the Fermi level. In previous studies, we demonstrated high tunneling magnetoresistance ratios of up to 1995% at 4.2 K and up to 354% at 290 K in magnetic tunnel junctions (MTJs) having Mn-rich Co 2 MnSi (CMS) electrodes [1], and 2610% at 4.2 K and 429% at 290 K in Mn-rich Co 2 (Mn, Fe)Si MTJs [2]. Furthermore, we have achieved efficient spin injection from Mn-rich CMS into GaAs via an ultra-thin CoFe insertion layer, resulting in electron spin polarization of up to 52% in GaAs at 4.2 K [3]. This value is more than one order of magnitude higher than those obtained for a Fe electrode or a CoFe electrode [4].