Correlation between electron spin resonance and magnetization in Gd5 Ge4

Electron spin resonance (ESR) across the field-induced antiferromagnetic (AFM) to ferromagnetic (FM) transition in Gd5 Ge4 has been studied. The AFM-FM transition can be characterized as an anomaly in the ESR spectrum. In the high-field FM state, a single strong ESR peak is observed while in the low-field AFM state, the ESR spectrum presents relatively weak double peaks. In the coexisting AFM and FM phases, the ESR spectrum is an asymmetrical double-peak structure due to a superposition of AFM and FM resonances. Thus, the ESR result is significantly correlated with magnetization. The g value for FM resonance is found to be close to g=1.992 for the free Gd3+ ion. The exchange interactions in the AFM state are discussed qualitatively.