[21a-E216-5~11] 10.3 スピンデバイス・磁気メモリ・ストレージ技術

▼ [21a-E216-7] The atomic ordering dependence of valence electronic structure in half-metallic Co₂Fe(Ga_0.5Ge_0.5) Heusler alloy observed by hard X-ray photoemission spectroscopy

〇(DC)Kazuki Goto^1,2、Yuya Sakuraba²、Yoshio Miura²、Ivan Kurniawan^1,2、Akira yasui³、Kumara Rosantha³、Chen Zixi^1,2、Tajiri Hiroo³、Akio Kimura⁴、Kazuhiro Hono^1,2 (1.Univ. of Tsukuba、2.NIMS、3.JASRI、4.Hiroshima Univ.)

キーワード：half-metal Heusler alloy, HAXPES, valence band structure

Recently, outstanding MR ratio over 50% at room temperature have been demonstrated in CPP-GMR devices using half-metallic Heusler alloy, Co₂FeGa_0.5Ge_0.5 (CFGG), which is promising for future applications such as a next generation read head for HDD. However, it is still an open question how much intrinsic spin-polarization in the bulk region (b) and how b changes against temperature. In this study, anoumalous XRD measrement was performed for CFGG thin films annealed at different temperature at BL13XU SPring-8 to quantitatively evaluate the degree of atomic ordering including the order between Co and Fe. AXRD result indicated that the higher temperature annealing improves Co-Fe ordering in CFGG. Then, hard X-ray photoemission spectroscopy (HAXPES) was also performed at BL09XU SPring-8 to observe how half-metallic valence band (VB) structure forms with atomic ordering. The experimentally observed variation of VB structure agrees well with the total DOS calculated by the ab initio calculation results for different atomic ordering. Furthermore the existence of in-gap state by Co-Fe disordering and the formation of half-metallic gap by improving Co-Fe ordering was directly observed by HAXPES measurement.