제목 [05/03] [colloquium] Roles of nonmagnetic elements in magnetic devices: first-principles studies
작성자 물리학과홈피 등록일 2016-04-25 오후 2:49:41 조회수 178
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[05/03] [colloquium] Roles of nonmagnetic elements in magnetic devices: first-principles studies
날 짜 : 2016년 5월 3일 화요일
시 간 : PM 4:30
장 소 : R404
연 사 :  홍순철 교수님(울산대학교)
제목:  Roles of nonmagnetic elements in magnetic devices: first-principles studies

  In this talk we discuss mainly effects of nonmagnetic elements on perpendicular magnetocrystalline anisotropy (PMCA), which is required in spintronic devices for enhancing areal recording density and reducing critical current density for writing information. The talk will be focused mainly on our recent first-principles calculational results of three systems; i) Fe/MgO(001) surface capped by 4d and 5d transition metals [TM/Fe/MgO(001)], ii) metastable phase of the body-centered-tetragonal ruthenium (bct–Ru), and iii) Pd(001) and Pd(111) thin films. In the TM/Fe/MgO(001) systems, strong PMCAs are found. The origin of the extremely large PMCA will be discussed by calculating the spin-channel decomposed contribution and electronic structure analyses. Strong hybridization between the d bands of TM and Fe in the minority spin state is revealed to be responsible for the sign changes of the MCA from parallel to perpendicular. A bct–Ru is identified to exhibit a large PMCA as well as an appreciable magnetic moment. The MCA energy is as large as 150 μeV/atom, two orders of magnitude greater than those of 3d magnetic metals. Further investigation over the range of tetragonal distortion suggests that the appearance of the magnetism in the bct–Ru is governed by the Jahn-Teller spit eg orbitals. Moreover, from band analysis, MCA is mainly determined by an interplay between two eg states, dx2−y2 and dz2 states, as a result of level reversal associated with tetragonal distortion. Finally we will present thickness-dependent magnetism of Pd(001) and Pd(111) thin films. The films are found to be stable in ferromagnetic states only for certain thicknesses. Stability of the ferromagnetic states is obviously triggered by quantum well states, rather than by surface termination. The thickness-dependent magnetism may be the origin of asymmetric magnetic behaviors observed in recent experiments on Pd/Co/Pd(111), which shows strong spin-orbit torque.  

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