Problems of spin and orbital dynamics associated with femtosecond optical magnetic reversal

Abstract

Features of the orbital and spin dynamics of ferromagnets irradiated by femtosecond laser pulses are discussed. A model in which only the orbital momenta of the electrons can change during femtosecond optical pumping is used. The spins undergo reorientation over the subnanosecond times characteristic of spin dynamics after the pump pulse ends. The spin reorientation is caused by the spin-orbital field of the orbital momenta created by the optical pump. Producing the coherent state of the nonequilibrium orbital momenta needed for spin reorientation requires suppression of the quantum fluctuations of the orbital momenta. These fluctuations are caused by tunnel transitions between degenerate (in terms of the sign of the magnetic quantum number) states of the orbital momenta in the crystal field. The possibility of suppressing them by an interatomic interaction of the orbital momenta, similar to the intra-atomic interorbital interaction responsible for Hund’s second rule, is discussed.