Spin-orbit torque properties of W-V alloy based magnetic heterostructures

다국어 초록 (Multilingual Abstract)

β-W is considered the most promising transition metal due to its outstanding charge-to-spin conversion efficiency. Despite this exceptional property, alloys based on β-W as a spin current generating layer have been rarely studied due to their lack of phase stability. This study examines various properties of W-V alloy layers in W100-xVx (5)/CoFeB (2.5)/MgO (1)/Ta (2) magnetic heterostructures with different W-V compositions. Samples were sputtered onto thermally oxidized Si wafers under a base pressure below 5 × 10<SUP>-9</SUP> Torr. Diverse W100-xVx compositions were fabricated by changing sputtering power densities of W and V targets during co-deposition. X-ray diffraction verified the existence of β-W up to a V content of 20 at%. It also confirmed that Co-V alloys are formed when V content exceeded 60 at%. Spin-orbit torque properties were analyzed by harmonics Hall measurement. Out of all the samples measured, the sample with W content of 80 at% and V of 20 at% showed the maximum damping-like torque efficiency of -0.45 ± 0.04. ξDL decreased drastically when V content exceeded 20 at% because phase transition from β-W to α-W occurred. We also fabricated heterostructures of W (5)/CoFeB (0.9)/MgO (1)/Ta (2) and W80V20 (5)/CoFeB (0.9)/MgO (1)/Ta (2) to obtain perpendicular magnetic anisotropy. These samples were used to acquire optical microscope images and determine switching current densities. We utilized Magneto-Optic Kerr Effect microscope to observe and obtain current-induced spin-orbit torque switching images for the W80V20 alloy-based sample. The change in the contrast of the images successfully depicted the magnetization switching of the ferromagnetic CoFeB layers. The switching current (current density) was 11 mA (2.2 × 10<SUP>7</SUP> A cm<SUP>-2</SUP>) and 6 mA (1.2 × 10<SUP>7</SUP> A cm<SUP>-2</SUP>) for β-W and W80V20, respectively. The switching current is clearly reduced when W80V20 is used instead of pristine W. We hope that this work will play as a key role in the field of spintronics in the future.
〈그림 본문참조〉