Laser-induced ultrafast spin dynamics in ErFeO3

Abstract

Using 100-fs optical laser pulses, we have been able to excite and probe spin dynamics in the rare-earth orthoferrite ${\mathrm{ErFeO}}_{3}$. The investigation was performed in a broad temperature range with the focus on the vicinities of the compensation point ${T}_{\mathrm{comp}}\ensuremath{\approx}47\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and the spin reorientation transition region in the interval $86\phantom{\rule{0.16em}{0ex}}\mathrm{K}\ensuremath{\lesssim}T\ensuremath{\lesssim}99\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Spin precession excited by the laser pulse was present in a large part of the investigated temperature range, but was especially strong near the spin reorientation region. In this region the laser pulse also caused an ultrafast spin reorientation. By changing the laser pulse fluence, we could vary both the reorientation amplitude and the reorientation speed. We show that the laser-induced spin dynamics in ${\mathrm{ErFeO}}_{3}$ is caused in part by heating and in part by the inverse Faraday effect. Comparing to the results of similar experiments in other rare-earth orthoferrites, we found the speed of the laser-induced spin reorientation to be significantly lower. We attribute this finding to the weaker electron-phonon coupling of the ${\mathrm{Er}}^{3+}$ 4f electrons with the lattice.