Spin polarization of Pt/Fe/MgO and Pt/MgO surfaces studied by spin-polarized positron beam

スピン偏極陽電子ビームを用いたPt/Fe/MgOとPt/MgO表面のスピン蓄積効果の研究

Zhang, H.; 深谷 有喜   ; 前川 雅樹; Li, H.; 河裾 厚男; 関 剛斎*; 吉野 達郎*; 齊藤 英治*; 高梨 弘毅*

Zhang, H.; Fukaya, Yuki; Maekawa, Masaki; Li, H.; Kawasuso, Atsuo; Seki, Takeshi*; Yoshino, Tatsuro*; Saito, Eiji*; Takanashi, Koki*

To directly observe the current-induced spin accumulation (CISP) on the outermost surface of Pt thin films, the Pt/Fe/MgO and Pt/MgO with different Pt thickness were prepared by magnetron sputtering and measured by using the newly-developed spin-polarized positron beam. The 3 annihilation fraction of Pt(25,50 nm)/Fe(1 nm)/MgO exhibited an asymmetry upon DC reversal suggesting the appearance of in-plane spin-polarized electrons on the outermost surface. The asymmetry of the 3 annihilation fraction of Pt(25)/Fe(1 nm)/MgO upon DC reversal disappears after rotating 90 degrees around the sample center, indicates that the CISP of the surface electrons is in-plane and perpendicular to the DC. The thickness dependence of CISP in Pt(t)/Fe(1nm)/MgO (t=25, 50, 75 nm) was studied. The estimated spin polarization of Pt(25 nm)/Fe(1 nm)/MgO was 0.11 at j=1.810 A/cm, which is nearly two times bigger than that of Pt(50 nm)/Fe(1nm)/MgO at the same current density. While for Pt(75 nm)/Fe(1 nm)/MgO surface no spin polarization was observed. The surface spin polarization of Pt(25 nm)/Fe(1nm)/MgO is nearly the same with that of Pt(25 nm)/AlO sample. This phenomenon implies that the surface spin polarization of Pt/Fe/MgO is not induced by the proximity ferromagnetism on the Pt/Fe interface.