[22p-B201-1~10] 10.1 Emerging materials in spintronics and magnetics (including fabrication and characterization methodologies)

▲ [22p-B201-10] Preparation and spin-orbit torque measurement of RuO₂/Co-Fe-B bilayer

〇Anh ThiVan Nguyen^1,2, Samik DuttaGupta^1,3, Yoshiaki Saito², Shunsuke Fukami^1,2,3,4,5, Duong Vu⁶, Hiroshi Naganuma^1,2, Shoji Ikeda^1,2, Tetsuo Endoh^1,2,3,4, Yasushi Endo^1,4 (1.CSIS, Tohoku Univ., 2.CIES, Tohoku Univ., 3.RIEC, Tohoku Univ., 4.ECEI, Tohohu Univ., 5.WPI-AIMR,Tohoku Univ, 6.IOP, VAST)

Keywords:Spin orbit torque induced magnetization switching, RuO2/Co-Be-B bilayer, effective SOT fields

Spin-orbit torque (SOT)-induced magnetization switching has attracted immense interest owing to its potential for high-performance spintronic devices such as SOT-MRAM [1,2], and material systems exhibiting large SOT are of great demand. So far, large SOT has been observed in heterostructures with 5d transition metals, whereas small SOT is expected in systems with 4d transition metals due to its small SOC [3]. As an effort to achieve a large SOT, however, some recent works have reported the SOT generation in antiferromagnetic RuO2 film thanks to its unique band structure [4], although the detailed investigation is lacking. Herein, we fabricate the (100)-oriented RuO2 film and evaluate SOT in a RuO2/Co-Fe-B bilayer by harmonic Hall measurement. RuO2 (4 nm)/Co-Fe-B (1.2 nm) bilayer was fabricated on an Al2O3(0001) substrate by DC/RF sputtering, where (100)-orientation of RuO2 with a three-domain structure is expected to be formed [5]. RuO2 layer was deposited by reactive sputtering at 300oC with a mixture of O2 gas (30%) and Ar gas. Ru (4 nm)/ Co-Fe-B (1.2 nm) bilayer was also fabricated for comparison. XRD pattern of a RuO2 film [Fig. 1(a)] shows only (h00) diffraction peaks of a rutile-type RuO2, proving the (100) orientation. The resistivity of RuO2 (100) film was determined as 247.4 mW.cm from the sheet resistance. The harmonic Hall measurement was performed for Hall bar devices of RuO2/Co-Fe-B and Ru/Co-Fe-B samples in a rotating magnetic field [Fig. 1(b), 1(c)]. A clear second harmonic signal is observed for RuO2/Co-Fe-B while it is negligible for Ru/Co-Fe-B, suggesting the SOT generation owing to the unique band structure of RuO2 [4]. The effective fields for the Slonczewski-like torque and field-like torque for RuO2/Co-Fe-B bilayer were obtained as m0H_SL = -0.11 mT and m0H_FL = -0.73 mT, respectively, at the current density of 6.5 MA/cm2. This result would be important for further research on the current-induced magnetization switching using antiferromagnets.