  We utilize spin Hall magnetoresistance (SMR) measurements to experimentally
investigate the pure spin current transport and magnetic properties of nickel
ferrite (NiFe2O4,NFO)/normal metal (NM) thin film heterostructures. We use
(001)-oriented NFO thin films grown on lattice-matched magnesium gallate
substrates by pulsed laser deposition, which significantly improves the
magnetic and structural properties of the ferrimagnetic insulator. The NM in
our experiments is either Pt or Ta. A comparison of the obtained SMR magnitude
for charge currents applied in the [100]- and [110]-direction of NFO yields a
change of 50% for Pt at room temperature. We also investigated the temperature
dependence of this current direction anisotropy and find that it is
qualitatively different for the conductivity and the SMR magnitude. From our
results we conclude that the observed current direction anisotropy may
originate from an anisotropy of the spin mixing conductance or of the spin Hall
effect in these Pt and Ta layers, and/or additional spin-galvanic contributions
from the NFO/NM interface.
