Semiconductor spintronics with Co2-Heusler compounds

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Ferromagnetic Co2-Heusler compounds showing high spin polarization have been utilized as spin injectors and detectors for III–V and Group-IV semiconductors. In this article, we first describe the progress in the crystal growth of Co2-Heusler films on GaAs(001) and Ge(111) by low-temperature molecular beam epitaxy. Next, some examples of electrical spin injection from Co2-Heusler contacts into GaAs and Ge through Schottky-tunnel barriers are introduced. Thanks to those efforts, it was found that Co2-Heusler compounds are useful for the realization of spin injection, transport, and detection in GaAs and Ge at room temperature. However, to achieve highly efficient spin transport, it is very important to suppress the interfacial out-diffusion of GaAs or Ge into the Co2-Heusler layer near the heterojunction. Recent progress in high-quality Co2-Heusler/Ge heterojunctions has demonstrated two-terminal magnetoresistance ratios of more than 0.1% at room temperature even for semiconductor spintronic device structures. The approach using Co2-Heusler compounds provides a powerful solution to the need for simultaneous achievement of highly efficient spin injection and low electric power at the source and drain contacts in semiconductor devices such as a spin MOSFET.Graphical abstract