Optical generation of nonzero-wave-vector magnons in antiferromagnetic MnF2

Abstract

Abstract New methods for the generation and detection of nonzero-wave-vector magnons are applied to a study of the dynamics of magnons in antiferromagnetic MnF2. The magnons are generated by pulsed optical excitation either of Er3+ centers into the upper level of the lowest 4F 9 2 (1) doublet followed by direct decay, or, at wave vectors close to the zone boundary, of a sideband of the 6A1g-4T1g transition of Mn2+ followed by breakup of exciton-magnon pairs. In the latter case, gradual lifting of degeneracy of the magnon branches permits both the intersublattice and intrasublattice rates to be measured. Detection is accomplished via the luminescence of the Er3+ center, or, at larger wave vectors, via the voltage induced in a pickup coil by the transient magnetization. Various decay processes are discussed in comparison with theoretical estimates.