Electron spin resonance and resistivity studies of charge-ordered Bi (1− x) Sr xMnO 3

Abstract

In this paper we report the temperature dependent electron spin resonance (ESR) and electrical resistivity studies of Bi (1− x) Sr x MnO 3 ( x = 0.3, 0.4, 0.45, and 0.5). The double integrated (DI) intensity of the ESR signal vs temperature ( T) and ln DI vs 1000/ T plots have been used to get information about magnetic interactions in the sample. A sharp change in the slope of this plot indicates the onset of long range antiferromagnetic (AFM) order. The Neel temperatures ( T N) of the sample increases with increase in Sr content. In the temperature range T > T N, domains of ferromagnetic (FM) and AFM correlations co-exist. The contributions of AFM correlations increase with the increase in Sr content. The observation of weak ESR signal in the temperature range below T N indicates the freezing of FM microdomains/inhomogeneities in the AFM long range ordered state. The resistivity ( ρ) data are analyzed in view of polaron model and variable range hopping (VRH) models given by Mott and Efros–Shklovskii (ES). As per Motts VRH model, ln ρ varies linearly with T −1/4 with a change in slope at T N. The estimated values of hopping distance and localization length are reasonable. It is also found that ln ρ varies linearly with T −1/2 in accordance with the ES VRH model. However, the estimated values of the model parameters are unrealistic. The ESR and resistivity data are also analyzed in view of phase separation (PS) model.