Spin-polarizations on ferromagnet surfaces observed by a spin-polarized positron beam

スピン偏極陽電子ビームを用いて磁性体の表面の電流誘起スピン蓄積効果を観測

Li, H.; Zhang, H.; 前川 雅樹; 深谷 有喜   ; 河裾 厚男

Li, H.; Zhang, H.; Maekawa, Masaki; Fukaya, Yuki; Kawasuso, Atsuo

Surface magnetic properties attract extraordinary interest concerning both fundamental and industrial viewpoints in spintronics. We investigated the surface spin-polarizations of conventional ferromagnets using spin-polarized positron beam (SPPB). The samples were Ni(001), Fe(001) and Co(001) single crystal films grown on MgO(001). After removing oxide over-layers by Ar ion sputtering, these were in-plane magnetized by a magnetic field of 0.04 T. Spin-polarized positron beam of energy of 50 eV was incident on the sample and positronium emitted into vacuum was observed. From the field-reversal effect on spin-triplet Ps formation, we evaluated the surface spin-polarizations. The spin-polarizations are positive 6-7% for Fe and Co, while negative 6% for Ni. The absolute values are much smaller than the spin-polarizations at the Fermi levels. Probably, positrons capture electrons located deeper than the Fermi levels. More details about underlying mechanism will be discussed.