Spectral characteristics of antiferromagnetic resonance of MnVG garnet

Antiferromagnetic resonance is detected in an $NaCa_2Mn_2V_3O_{12}$ crystal which contains octahedral $Mn^{2+}$ ions. It is established that there is an isotropic slot ($\Delta ^2$) in the antiferromagnetic resonance spectrum of the crystal, whose value is maximal at T $\sim$ 7K and is sharply reduced with a reduction in temperature. The results of measurements of the static magnetostriction of the same crystal justifies the hypothesis that $\Delta ^2$ is not related to the magnetoelastic interaction. The possible mechanism of the observed characteristics of the antiferromagnetic resonance in this crystal is discussed. This is interaction of the Jahn-Teller admixtures of the $Mn^{3+}$ ions in the crystal.