Effects of Size, Shape, and Frequency on the Antiferromagnetic Resonance Linewidth of MnF2

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Abstract
Experimental measurements of the antiferromagnetic resonance in MnF2 at 4.2°K have been made as a function of microwave frequency and sample size and shape. Measurement frequencies ranged from 100 to 305 GHz. The experimental data have been analyzed with the aid of a newly derived electrodynamic treatment of the experimental arrangement combined with a molecular field theoretic calculation of the rf permeability tensor for MnF2. Agreement between experiment and theory is good using only a one‐parameter fit. It was found that the linewidth is not strongly frequency dependent in very good samples except at frequencies very near to or very far from the zero‐field resonance frequency. The effect of sample size on observed linewidth is very significant. A value of 90 Oe is given for the residual size‐independent linewidth. Experimental aspects are emphasized due to the extremely high frequencies employed.