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Thickness and composition-dependent spin-orbit torque behaviors in perpendicularly magnetized Ta/W (t)/CoFeB and Ta1-xWx/CoFeB junction structures

Authors
Cha, In HoKim, TaehyunKim, Yong JinKim, Gyu WonKim, Young Keun
Issue Date
15-5월-2020
Publisher
ELSEVIER SCIENCE SA
Keywords
Ta-W; Alloy; Spin-orbit torque; Perpendicular magnetic anisotropy; Switching current; Microstructure
Citation
JOURNAL OF ALLOYS AND COMPOUNDS, v.823
Indexed
SCIE
SCOPUS
Journal Title
JOURNAL OF ALLOYS AND COMPOUNDS
Volume
823
URI
https://scholar.korea.ac.kr/handle/2021.sw.korea/55687
DOI
10.1016/j.jallcom.2020.153744
ISSN
0925-8388
Abstract
The spin-orbit torque (SOT) generated in normal metal (NM)/ferromagnet (FM) junctions is of technological interest as it can reduce the critical current density required for magnetization switching in memory devices. Ta and W, 5d NMs, exhibit large spin-orbit couplings and are compatible with the semiconductor processing. In this study, we investigate variations in SOT properties of Ta/W(t)/CoFeB/MgO/Ta (bilayer NM structures, where t is the W thickness) and Ta1-xWx/CoFeB/MgO/Ta (alloyed NM structures, where x is the W concentration in at%) junctions prepared on Si substrates with thermal oxides. In the former structure, the effective spin-orbit torque (SOT) field gradually increases with the W thickness reaching its maximum at 2.0 nm, followed by a decrease. In the latter structure, the effective SOT field behaves differently in the Ta- and W-rich regions. In-plane-current-induced switching measurements show similar trends, where the minimum and maximum switching current densities for the bilayer and alloyed NM structures are 3.4-10.3 and 0.81 to 6.3 x 10(7) A/cm(2), respectively. Microstructural analyses by X-ray diffraction and transmission electron microscopy suggest that the crystal phase of W changes from the amorphous to the alpha phase in the bilayer NM structure with the increase in the W thickness and the alloyed NM structure with the change in the concentration. (C) 2020 Elsevier B.V. All rights reserved.
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공과대학 (신소재공학부)
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