Transition metal dichalcogenides (TMDs) are potential materials for exerting efficient spin-orbit torque (SOT) on the adjacent ferromagnetic (FM) layer due to their high spin-orbit coupling (SOC) and broken inversion symmetry at the interface 1. An unconventional SOT is recently observed in WTe2/NiFe heterostructures due to low symmetry in WTe2 2. PtSe2 is one of the TMDs having high SOC 3. In this work, we measured the effective spin Hall efficiency (SHE) in PtSe2/NiFe/Pt heterostructure using spin-torque ferromagnetic resonance (STFMR). PtSe2 was synthesized by salinization of a sputtered Pt (3 nm) film. The growth of PtSe2 was confirmed using Raman measurements, which shows two peaks at 176 cm-1 (Eg) and 206 cm-1 (A1g). Subsequently, a 6 nm thick NiFe (Py) layer followed by Pt (3 nm) capping layer was deposited on PtSe2 using magnetron sputtering. For STFMR measurements, RF current of frequency varying from 3 GHz to 7 GHz was applied to the device in the presence of an external magnetic field (H). The mixing voltage (Vmix) across the device was measured and the symmetric & anti-symmetric components (VS, VA) of Vmix, linewidth (ΔH), and resonance field (Hr) were extracted (Fig.1) from the fitting of STFMR spectra. Effective SHE was calculated using the ratio of VS and VA and found to be increased 33% for PtSe2/Py/Pt compared to reference (Py/Pt). This change in SHE is due to the presence of PtSe2, which was further confirmed by making a stack with Pt/Py/Pt structure. STFMR signal of all three stacks has been compared in Fig. 1 (a). No clear signal was observed for Pt/Py/Pt which confirms the presence of SOT due to PtSe2. Damping parameter was extracted by the fitting of linewidth (ΔH) vs. frequency (f) curve (Fig. 2) and was found to be enhanced by 131% in the case of PtSe2/Py/Pt compared to its reference Py/Pt. Large enhancement in damping parameter indicates large spin pumping into PtSe2. These results indicate the suitability of using PtSe2 as a potential material for spin-orbit torque.
1 Q. Shao et al., Nano Letter 16, 7514-7520 (2016) 2 D. MacNeill et. al., Nature Physics, 13, 300-305 (2017) 3 Marcin Kurpas and Jaroslav Fabian, Physical Review B, 103, 125409 (2017)