Large negative uniaxial magnetic anisotropy in highly distorted Co-ferrite thin films

The strain induced magnetic anisotropy (MA) of epitaxial Co-ferrite (CFO) thin films grown on MgAl2O4(001) (MAO) by reactive sputtering was studied. These films underwent large tetragonal compressive strain due to the lattice mismatch between the substrates and films, resulting in tetragonalities of up to −0.04. Scanning transmission electron microscopy observation combined with fast Fourier transform analysis revealed that the lattice distortion monotonically relaxed with the increasing film thickness. Unlike the CFO(001) films on MgO(001) substrates, a magnetically enhanced layer exists at the interface between CFO and MAO. A large negative uniaxial MA energy of −5.9 MJ/m3 was confirmed for the thinnest film of 12.9 nm at 300 K by magneto-torque measurements. The induced uniaxial anisotropy decreased with the increasing film thickness owing to misfit relaxation. The magneto-elastic (ME) constant, which was determined by a fitting line for films with different thicknesses and therefore different tetragonalities, was 0.15±0.01 GJ/m3. This result is consistent with the value of 0.14 GJ/m3 for the bulk and suggests that the framework of the phenomenological ME theory for CFO is valid for a wide range of tetragonalities, at least up to −0.04. Our results also indicate that the misfit engineering of CFO thin films has great potential in inducing enhanced uniaxial MA

Spin Hall magnetoresistance at the interface between platinum and cobalt ferrite thin films with large magnetic anisotropy

The recently discovered spin Hall magnetoresistance (SMR) effect is a useful means to obtain information on the magnetization process at the interface between a nonmagnetic metal and ferromagnetic insulators. We report the SMR measurements at the interface between platinum and cobalt ferrite thin films for samples with two different preferential directions of magnetization (out-of-plane and in-plane). The directional difference of the magnetic easy axis does not seem to influence the value of SMR