Temperature-dependent spin-polarized electronic structure of the half-metallic Heusler alloy CoMnSi films

Sumida, Kazuki   ; Kakoki, Masaaki*; Sakuraba, Yuya*; Masuda, Keisuke*; Kono, Takashi*; Goto, Kazuki*; Miyamoto, Koji*; Miura, Yoshio*; Hono, Kazuhiro*; Okuda, Taichi*; Kimura, Akio*

Heusler alloy CoMnSi is theoretically predicted to be a half-metal ferromagnet exhibiting 100 spin-polarization. In fact, a huge output has been reported for tunnel magnetoresistance (TMR) devices using CoMnSi films. However, such a giant TMR ratio is observed only at low temperatures, and the output drastically decreases at room temperature. Several theoretical models have been proposed for the spin-depolarization at room temperature, but the mechanism remains unclear. In this study, we have fabricated CoMnSi films and performed temperature-dependent spin- and angle-resolved photoelectron spectroscopy. We confirmed a steep hole-band at point and electron-band at X point. Those experimentally observed bands are well reproduced by the calculations. More importantly, the temperature-dependent spin-polarization can be nicely fitted by Bloch law. This implies that the spin-depolarization can be explained by the thermally excited magnon model.