Vectorial observation of the spin Seebeck effect in epitaxial NiFe2O4 thin films with various magnetic anisotropy contributions

Abstract

We have developed a vectorial type of measurement for the spin Seebeck effect (SSE) in epitaxial NiFe2O4 thin films which have been grown by pulsed laser deposition on MgGa2O4 with (001) and (011) orientations as well as CoGa2O4 (011), thus varying the lattice mismatch and crystal orientation. We confirm that a large lattice mismatch leads to strain anisotropy in addition to the magnetocrystalline anisotropy in the thin films using vibrating sample magnetometry and ferromagnetic resonance measurements. Moreover, we show that the existence of a magnetic strain anisotropy in NiFe2O4 thin films significantly impacts the shape and magnitude of the magnetic-field-dependent SSE voltage loops. We further demonstrate that bidirectional field-dependent SSE voltage curves can be utilized to reveal the complete magnetization reversal process, which establishes a vectorial magnetometry technique based on a spin caloric effect.