Impurity Magnons in MnF2:Co

Abstract

Complete understanding of magnetic impurity modes can be obtained from their energies and wavefunctions. Energies are obtained from absorption, Raman, and fluorescent measurements but wavefunction information from g factors is most useful when the impurity and host g factor are very dissimilar. To this end, impurity modes in MnF2:Co2+ have been studied by far ir absorption and Raman scattering, respectively. The g factor for the s0 mode is measured to be 3.21 and differs substantially from 4.24, the value obtained by EPR in the diamagnetic isomorph MgF2. The s0 energy and g factor can be explained consistently by exchange mixing of the ground state with excited orbital states of Co2+. The g factor for the pair mode at 170.3 cm−1 was found to be 1.61, significantly larger than g (s0) - g (Mn2+) = 1.2. The Ising pair mode energies and g factors have been renormalized by including transverse exchange to second order. The correct energies for the impurity modes are obtained but the g factors of the pair modes do not agree with experiment. Higher-order spin interactions produced by the orbital motion on the cobalt ion do not significantly alter this result.