Influence of Impurities to EPR in Two-Dimensional Antiferromagnet K₂MnF₄

Abstract

The EPR linewidth and the line shape of impurity-doped two-dimensional antiferromagnets K₂Mn_cMg_1−cF₄ (c\gtrsim0.35) in X-band region were investigated at room temperature. The minimum of the linewidth at a “magic angle” θ=55° (θ is the angle of dc field with respect to the c axis of the crystal) was observed indicating the dominancy of q\simeq0 diffusive mode in the dipolar interaction. The line shape at θ=0° approaches to Gaussian from nearly Lorentzian decreasing Mn contents. This fact can be explained by the formation of the broken chains of Mn atoms in the crystal. The calculated line shape for Mn chain consisting of 30 atoms agrees with the experimental results for c=0.35.
The low-temperature line-broadening of the impure two-dimensional systems was suppressed and the minimum of the width at the “magic angle” did not disappear even at the lowest temperatures on the contrary to the pure systems.