Electronic spin resonance study of perovskite-type manganites

The electron spin resonance behavior of two typical systems with Mn3+/Mn4= 2:1 and 1:1 within the temperature range T>T-C is studied experimentally. The results show that there exists a temperature T-min(>T-C)dividing the m agnetic behavior above T-C into two distinguishable regime. While T>T-min, The ESR spectrum consists of one symmetrical resonance line. The Lande fact or is independent of temperature and close to the value of free electron (s imilar to 2.0023), and the linewidth increases linearly with increasing tem perature. Some distortions are observed when the temperature is lower than T-min. The line shape becomes unsymmetrical. The g factor become dependent on the temperature and the linewidth increases anomalously with decreasing temperature. These results point out that the complete paramagnetism exits only in the temperature range T>T-min. When T-C<T<T-min, the anomalous para magnetic behavior may be caused by the magnetic inhomogeneity. The mechanis m of resonance linewidth broadening is discussed based on an analysis of th e linewidth above T-min, suggesting that the exchange narrowing spin-spin i nteraction and the spin-lattice interaction are two possible reasons of lin ewidth changes in the high temperature regime.