title: Competing Anisotropy-Tunneling Correlation of the CoFeB/MgO Perpendicular Magnetic Tunnel Junction: An Electronic Approach.
abstract: We intensively investigate the physical principles regulating the tunneling magneto-resistance (TMR) and perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO magnetic tunnel junction (MTJ) by means of angle-resolved x-ray magnetic spectroscopy. The angle-resolved capability was easily achieved, and it provided greater sensitivity to symmetry-related d-band occupation compared to traditional x-ray spectroscopy. This added degree of freedom successfully solved the unclear mechanism of this MTJ system renowned for controllable PMA and excellent TMR. As a surprising discovery, these two physical characteristics interact in a competing manner because of opposite band-filling preference in space-correlated symmetry of the 3d-orbital. An overlooked but harmful superparamagnetic phase resulting from magnetic inhomogeneity was also observed. This important finding reveals that simultaneously achieving fast switching and a high tunneling efficiency at an ultimate level is improbable for this MTJ system owing to its fundamental limit in physics. We suggest that the development of independent TMR and PMA mechanisms is critical towards a complementary relationship between the two physical characteristics, as well as the realization of superior performance, of this perpendicular MTJ. Furthermore, this study provides an easy approach to evaluate the futurity of any emerging spintronic candidates by electronically examining the relationship between their magnetic anisotropy and transport.
authors.affiliation: Department of Materials Science &Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, 30010, Taiwan, R.O.C.
authors.forename: Chao-Yao
authors.initials: CY
authors.lastname: Yang
authors.affiliation: Department of Materials Science &Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, 30010, Taiwan, R.O.C.
authors.forename: Shu-Jui
authors.initials: SJ
authors.lastname: Chang
authors.affiliation: Undergraduate Honors Program of Nano Science and Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, 30010, Taiwan, R.O.C.
authors.forename: Min-Han
authors.initials: MH
authors.lastname: Lee
authors.affiliation: Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsin-Chu, Taiwan 30010, R.O.C.
authors.forename: Kuei-Hung
authors.initials: KH
authors.lastname: Shen
authors.affiliation: Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsin-Chu, Taiwan 30010, R.O.C.
authors.forename: Shan-Yi
authors.initials: SY
authors.lastname: Yang
authors.affiliation: National Synchrotron Radiation Research Center, Taiwan, 101 Hsin Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan, R.O.C.
authors.forename: Horng-Ji
authors.initials: HJ
authors.lastname: Lin
authors.affiliation: Department of Materials Science &Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, 30010, Taiwan, R.O.C.
authors.forename: Yuan-Chieh
authors.initials: YC
authors.lastname: Tseng