Influence of Sample Preparation on Spin Glass Behavior at the Ni/MoS₂ Interface

Incorporating MoS2 substrates into spintronic devices requires a thorough understanding of the properties of their interface with ferromagnetic metals. To this end, we investigated the magnetic properties of Ni/MoS2 samples fabricated under several different conditions. Depositing Ni using electron beam evaporation resulted in spin glass-like behavior, suggestive of a superspin glass (SSG) state. In samples where Ni was deposited on MoS2 substrates previously annealed at 300°C, the time relaxation of the magnetoresistance was significantly more rapid compared to unannealed samples. Scanning tunneling microscopy images reveal that Ni forms circularly symmetric structures with a circular diameter of two nanometers in both the annealed and unannealed samples. Samples created by depositing Ni using thermal evaporation also resulted in a granular Ni structure. However, the Ni grains were no longer circularly symmetric; rather, they were ellipsoidal. These samples also resulted in SSG behavior, including slow relaxation, memory, and rejuvenation. Thus, the magnetic behavior of granular Ni films does not seem to depend sensitively on the shape of the grains. At the same time, annealing reduces disorder at and near the interface, which does result in significant changes in glassy dynamics.