# Vectorial observation of the spin Seebeck effect in epitaxial NiFe$_2$O$_4$ thin films with various magnetic anisotropy contributions

## TL;DR

This study introduces a vectorial measurement method for the spin Seebeck effect in epitaxial NiFe₂O₄ thin films, revealing how magnetic strain anisotropy influences SSE signals and enabling a new magnetometry technique.

## Contribution

The paper presents a novel vectorial measurement approach for SSE in epitaxial NiFe₂O₄ films, demonstrating the impact of magnetic strain anisotropy on SSE signals and establishing a vectorial magnetometry method.

## Key findings

- Large lattice mismatch induces strain and magnetocrystalline anisotropy.
- Magnetic strain anisotropy affects SSE voltage shape and magnitude.
- Bidirectional SSE curves enable complete magnetization reversal detection.

## Abstract

We have developed a vectorial type of measurement for the spin Seebeck effect (SSE) in epitaxial NiFe$_2$O$_4$ thin films which have been grown by pulsed laser deposition on MgGa$_2$O$_4$ (MGO) with (001) and (011) orientation as well as CoGa$_2$O$_4$ (011) (CGO), 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 NiFe$_2$O$_4$ 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.