Experimental study of antiferromagnetic resonance in noncollinear antiferromagnet Mn$_{3}$Al$_{2}$Ge$_{3}$O$_{12}$

TL;DR

This study measures antiferromagnetic resonance in Mn$_{3}$Al$_{2}$Ge$_{3}$O$_{12}$ across a broad frequency and field range, confirming theoretical models and revealing hysteresis linked to domain structures.

Contribution

First comprehensive experimental AFMR frequency-field data for Mn$_{3}$Al$_{2}$Ge$_{3}$O$_{12}$, validating hydrodynamic theory and exploring domain-related hysteresis effects.

Findings

Three AFMR modes observed with zero field gaps of 40 and 70 GHz

Hysteresis and history dependence of resonance absorption near gap frequencies

AFMR signals detected at 1 to 5 GHz frequencies near spin-reorientation transition

Abstract

We have measured antiferromagnetic resonance (AFMR) frequency-field dependences for aluminum-manganese garnet Mn$_{3}$Al$_{2}$Ge$_{3}$O$_{12}$ at frequencies from 1 to 125 GHz and at the fields up to 60 kOe. Three AFMR modes were observed for all orientations, their zero field gaps are about 40 and 70 GHz. Andreev-Marchenko hydrodynamic theory [Sov. Phys. Usp. 130, 39 (1980)] well describes experimental frequency-field dependences. We have observed hysteresis of resonance absorption as well as history dependence of resonance absorption near gap frequencies below 10 kOe in all three measured field orientations, which are supposedly due to the sample domain structure. Observation of the AFMR signal at the frequencies from 1 to 5 GHz allows to estimate repulsion of nuclear and electron modes of spin precession in the vicinity of spin-reorientation transition at H||[100].