Enhanced magnon spin transport in NiFe$_2$O$_4$ thin films on a lattice-matched substrate

TL;DR

This study demonstrates enhanced magnon spin transport in epitaxial NiFe₂O₄ thin films grown on lattice-matched substrates, showing improved properties and magnon relaxation length comparable to yttrium iron garnet, with evidence of magnon polaron formation.

Contribution

It reports the first observation of enhanced magnon transport in NiFe₂O₄ films on lattice-matched substrates, highlighting improved magnetic properties and magnon relaxation length.

Findings

Magnon relaxation length around 2.5 μm at room temperature.

Enhanced magnon signals in nonlocal transport experiments.

Evidence of magnon polaron formation at various temperatures.

Abstract

We investigate magnon spin transport in epitaxial nickel ferrite (NiFe$_2$O$_4$, NFO) films grown on magnesium gallate spinel (MgGa$_2$O$_4$, MGO) substrates, which have a lattice mismatch with NFO as small as 0.78%, resulting in the reduction of antiphase boundary defects and thus in improved magnetic properties in the NFO films. In the nonlocal transport experiments, enhanced signals are observed for both electrically and thermally excited magnons, and the magnon relaxation length ($\lambda_m$) of NFO is found to be around 2.5 $\mu$m at room temperature. Moreover, at both room and low temperatures, we present distinct features from the nonlocal spin Seebeck signals which arise from magnon polaron formation. Our results demonstrate excellent magnon transport properties (magnon spin conductivity, $\lambda_m$ and spin mixing conductance at the interface between Pt) of NFO films grown on a lattice-matched substrate that are comparable with those of yttrium iron garnet.