Facet-dependent magnon-polarons in epitaxial ferrimagnetic Fe3O4 thin films

TL;DR

This study experimentally observes facet-dependent magnon-polarons in epitaxial Fe3O4 thin films, revealing how crystal orientation influences their properties and potential for spintronic device manipulation.

Contribution

It reports the first observation of facet-dependent magnon-polarons in Fe3O4 thin films and links phonon velocity differences to magnetic field thresholds.

Findings

Critical magnetic fields differ for (110) and (100) orientations.

Magnon-polarons influence spin Seebeck voltage with temperature.

Crystal orientation affects magnon-polaron behavior.

Abstract

Magnon-polarons are coherently mixed quasiparticles that originate from the strong magnetoelastic coupling of lattice vibrations and spin waves in magnetic-ordered materials. Recently, magnon-polarons have attracted a lot of attention since they provide a powerful tool to manipulate magnons, which is essential for magnon-based spintronic devices. In this work, we report the experimental observation of facet-dependent magnon-polarons in epitaxial ferrimagnetic Fe3O4 thin films via spin Seebeck effect measurement. The critical magnetic fields for the magnon-polarons in the (110)- and (100)-oriented Fe3O4 films are 1.5 T and 1.8 T, respectively, which arises from the different phonon velocities along the [110] and [100] directions. As the temperature decreases, the magnon-polarons-enhanced spin Seebeck voltage decreases in both (110)- and (100)-oriented Fe3O4 films, which could be attributed to the enhanced magnon-polarons scattering at elevated temperatures. This work demonstrates the crystal structure engineering in epitaxial magnetic films as a promising route to manipulate the magnon-polarons for future magnon spintronic applications.