Ultrafast Control of Magnetic Anisotropy by Resonant Excitation of 4f Electrons and Phonons in Sm0.7Er0.3FeO3

Abstract

We compare the ultrafast dynamics of the spin reorientation transition in the orthoferrite Sm0.7Er0.3FeO3 following two different pumping mechanisms. Intense few-cycle pulses in the midinfrared selectively excite either the f-f electronic transition of Sm3+ or optical phonons. With phonon pumping, a finite time delay exists for the spin reorientation, reflecting the energy transfer between the lattice and 4f system. In contrast, an instantaneous response is found for resonant f-f excitation. This suggests that 4f electronic pumping can directly alter the magnetic anisotropy due to the modification of 4f-3d exchange at femtosecond timescales, without involving lattice thermalization.