Optimization of growth of large-area SnS thin films and heterostructures for spin pumping and spin-orbit torque

Two-dimensional (2D) van der Waals materials are promising for spintronics due to their unique physical properties down to the monolayer thickness. Tin monosulfide (SnS) is a van der Waals material belonging to the monochalcogenide family, lacking mirror symmetry in its crystal structure. Monolayer SnS also exhibits spin-splitting band structure as well as in-plane ferroelectricity. In this work, we investigate the potential of SnS for spintronic applications by optimizing the growth of large-area 2D thin films of SnS on a CMOS-compatible Si/SiO2 substrate using pulsed laser deposition. We perform a comprehensive SnS thickness-dependent spin pumping study in SnS/Ni80Fe20 system for SnS films grown at 300 and 473 K. The thickness dependence of the damping constant of Ni80Fe20 agreed with the theory of spin pumping only for optimized SnS layers grown at 300 K, exhibiting low and thickness-independent surface roughness. The effective spin mixing conductance of SnS/Ni80Fe20 for optimized SnS layers grown at 300 K is estimated to be (8.83 +/- 1.15) nm-2. We also performed spin-torque ferromagnetic resonance (STFMR) measurements on the SnS (1.3 nm)/Ni80Fe20 devices for the optimized SnS layers grown at 300 K. Through angle-resolved STFMR measurements, we show the presence of unconventional spin-orbit torques in SnS. Our findings suggest that SnS is promising for emerging spintronic devices.