Thermal transport in MnF2. II. Magnetic field effects

Abstract

The thermal conductivity of the antiferromagnet Mn${\mathrm{F}}_{2}$ has been measured in magnetic fields up to 60 kOe for temperatures between 4.2 and 0.3 K. The conductivity does not change in fields applied parallel to the [001] easy axis of magnetization. This is in disagreement with calculations of the boundary-limited magnon conductivity. Possible explanations for the absence of magnon heat transport are discussed. Variations in the conductivity for fields applied at an angle to the [001] direction are shown to be due to an increase in the resonant frequency for phonon scattering by O${\mathrm{H}}^{\ensuremath{-}}$ impurities. This is explained in terms of the tunneling model for the O${\mathrm{H}}^{\ensuremath{-}}$ states that was outlined in the preceding paper. Because of the magnetoelastic interaction, an off-axis magnetic field creates static strains in the crystal which increase the tunnel splitting.