Optically-induced frequency up-conversion of the ferromagnetic resonance in an ultrathin garnet

TL;DR

This study demonstrates that ultrafast optical pulses can increase the ferromagnetic resonance frequency in ultrathin garnet films by modifying magnetic anisotropy, revealing new ways to control magnetic properties optically.

Contribution

It shows that optical heating can unexpectedly raise the ferromagnetic resonance frequency via anisotropy modification in nanometer-thick garnet films.

Findings

Optical heating increases FMR frequency up to 20%.

Both one- and two-photon absorption trigger spin dynamics.

Conditions for effective optical control of magnetic anisotropy are identified.

Abstract

We perform ultrafast pump-probe measurements on a nanometer-thick crystalline Bi-doped yttrium iron garnet film with perpendicular magnetic anisotropy. Tuning the photon energy of the pump laser pulses above and below the material's bandgap, we trigger ultrafast optical and spin dynamics via both one- and two-photon absorption. Contrary to the common scenario, the optically-induced heating of the system induces an increase up to 20% of the ferromagnetic resonance frequency. We explain this unexpected result in terms of a photo-induced modification of the magnetic anisotropy, i.e. of the effective field, identifying the necessary conditions to observe this effect. Our results disclose the possibility to optically increase the magnetic eigenfrequency in nanometer-thick magnets.