Microwave absorption anomalies due to the low dimensionality of the magnetic structure of BaMnF4

We investigate absorption bands due to two-magnon processes under parallel microwave pumping. The frequency-field diagram of these bands is determined for different crystal orientations relative to the external field. The value of the weak exchange interaction in the system (J'/J≈10−4) is found from an analysis of the shape of the total absorption band. We find that in an external magnetic field the homogeneous resonance line undergoes an anomalous change in width and a change in its position as the result of the decay of the homogeneous (k = 0) magnon of the high-frequency branch of the spectrum into two magnons of the low-frequency branch. The results are shown to be in good agreement with the predictions of the theory.

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