Optical Frequency Up-Conversion of the Ferromagnetic Resonance in an Ultrathin Garnet Mediated by Magnetoelastic Coupling

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 band gap, we trigger ultrafast optical and spin dynamics via both one- and two-photon absorption. Contrary to the common scenario, the optically induced excitation induces an increase up to 20% of the ferromagnetic resonance frequency of the material. We explain this unexpected result in terms of a modification of the magnetic anisotropy caused by a long-lived photo-induced strain, which transiently and reversibly modifies the magnetoelastic coupling in the material. Our results disclose the possibility to optically increase the magnetic eigenfrequency in nanometer-thick magnets.

Automated summary

In this study, ultrafast pump-probe measurements were performed on a nanometer-thick Bi-doped yttrium iron garnet film, revealing that optically induced excitation can increase the ferromagnetic resonance frequency of the material by up to 20%. This unexpected result is explained by a modification of the magnetic anisotropy caused by long-lived photo-induced strain that transiently and reversibly modifies the magnetoelastic coupling in the material.