Antiferromagnetic resonance linewidth in MnF 2 near the transition temperature

Abstract

The antiferromagnetic resonance (AFMR) linewidth of MnF 2 was studied near the Néel temperature. In the presence of an applied magnetic field, the linewidth diverges approximately as |T−T N| − 5 6 . In the absence of an applied field, the line-width is larger and diverges approximately as |T−T N| − 4 3 . The linewidth is independent of the direction of the magnetic field and is the same for both branches of the AFMR spectrum. Though qualitative attempts to explain the temperature dependence both in the presence and absence of an applied magnetic field were made, a detailed theoretical explanation is still lacking. The independence of the linewidth on applied magnetic field direction and on AFMR mode are what we expect intuitively, although work by Mori and Kawasaki suggests that the linewidths for the two branches of the AFMR spectrum ought to be different. Above T N electron paramagnetic resonance (EPR) in MnF 2 was observed. For H parallel to c, at temperatures near T N , the linewidth increases approximately as |T−T N| − 3 8 . A smaller increase occurs for H perpendicular to c. The EPR data are discussed relative to the work of Heller and Benedek and of Moriya.