Role of interface quality for the spin Hall magnetoresistance in nickel ferrite thin films with bulk-like magnetic properties

We utilized spin Hall magnetoresistance (SMR) measurements to experimentally investigate pure spin current transport in thin film heterostructures of nickel ferrite (NiFe₂O₄,NFO) and normal metals (NM) Ta and Pt. We grew (001)-oriented NFO thin films by pulsed laser deposition on lattice-matched magnesium gallate (MgGa₂O₄) substrates, thereby significantly improving their magnetic and structural properties. We performed SMR measurements at room temperature in patterned Hall bar structures for charge currents applied in the [100]- and [110]-directions of NFO. We found that the extracted SMR magnitude for NFO/Pt heterostructures depends crucially on the Pt resistivity of the investigated Hall bar structure. We further study this resistivity scaling of the SMR effect at different temperatures for NFO/Pt. Our results suggest that the spin mixing conductance of the NFO/Pt interface and the Pt resistivity depend on the interface quality and thus a correlation between these two quantities exists.