Enhanced Room-Temperature Spin Hall Magnetoresistance in Single-Domain BiFeO₃ and Pt Bilayer

Spin Hall magnetoresistance (SMR) is an effect arising at the interface between a heavy metal and a magnetic insulator. Here, we report the magnetic-field and temperature dependence of longitudinal SMR in BiFeO₃/Pt bilayer samples. Multiferroic BiFeO₃ epitaxial thin films are grown on STO (001) substrates with a 4° miscut toward [110], resulting in a single ferroelectric/ferroelastic domain, which is verified by piezoresponse force microscopy (PFM) and reciprocal space mapping (RSM). The first-harmonic SMR in the BiFeO₃/Pt samples shows a typical cos[2(φ-φ₀)] dependence, where φ is the angle between the current and the external magnetic field, with a SMR amplitude that increases quadratically with field magnitude as expected for an antiferromagnet/metal sample. However, unlike the usual SMR in ferromagnet/metal or antiferromagnet/metal samples, BiFeO₃/Pt has the maximum SMR signal at an angle different than φ₀ = 0° or 90°. We believe that this might be due to the more complicated spin structure associated with the spin cycloid, which can be further probed from various other techniques such as neutron diffraction and non-resonant x-ray magnetic scattering (NXMS).