Quantum theory of femtosecond optomagnetic effects for rare-earth ions in DyFeO3

Abstract

Our theoretical analysis shows that a femtosecond laser pulse can efficiently launch magnetization dynamics of ${\mathrm{Dy}}^{3+}$ ions in ${\mathrm{DyFeO}}_{3}$ and ${\mathrm{DyAlO}}_{3}$. Excitation of electrons from the ground state to the low-lying electronic level of ${\mathrm{Dy}}^{3+}$ ions by circularly or linearly polarized light can be seen as a result of an effective magnetic field acting on the magnetic moments of the rare-earth ions. It is shown that the launched magnetization dynamics can be expressed as a combination of coherent oscillations of mutually parallel and mutually antiparallel magnetic moments of ${\mathrm{Dy}}^{3+}$ ions, respectively. While the antiparallel magnetic moments lie in the plane perpendicular to the wave vector of light in the medium $\mathbit{k}$, the parallel magnetic moments are aligned along $\mathbit{k}$. The magnetization dynamics depend strongly on the duration and the shape of the pumping laser pulse, as well as on the anisotropy in properties of the rare-earth ion.