Two-magnon inelastic light scattering in the antiferromagnetsCoF2andNiF2: Experiment and theory

Abstract

Experimental measurements for the two-magnon Raman scattering in the rutile-structure antiferromagnets ${\mathrm{CoF}}_{2}$ and ${\mathrm{NiF}}_{2}$ are reported. For ${\mathrm{CoF}}_{2}$ the temperature and polarization dependences of the two-magnon scattering are investigated up to the N\'eel temperature ${T}_{N}$. An effective spin model is employed to obtain a good theoretical description of the line shapes and peak frequencies for temperatures up to $0.4{T}_{N}$. For ${\mathrm{NiF}}_{2}$, we present results for the polarization characteristics of the scattering at low temperatures $T\ensuremath{\ll}{T}_{N}$. A theoretical model similar to that employed for ${\mathrm{CoF}}_{2}$ is used to compare with the experimental measurements and good agreement is obtained for the line shapes and peak frequencies. Results are also deduced for some exchange and anisotropy parameters and the relative magnitudes of the magneto-optical coefficients in the interaction Hamiltonian for both ${\mathrm{CoF}}_{2}$ and ${\mathrm{NiF}}_{2}$.