Electron spin resonance study of Bi(1−x)CaxMnO3

Abstract

The temperature dependent electron spin resonance (ESR) studies on Bi(1−x)CaxMnO3 (x=0.4, 0.45, and 0.5) having a triclinic structure were carried out to understand the spin dynamics, short-range magnetic interactions, and micromagnetic phase formation in these materials. The phase transition into charge-ordered (CO) state takes place at temperatures TCO=313K (for x=0.4 and 0.5) and at 317K (for x=0.45) samples. The data are explained in view of the existence of mixed valence clusters of Mn3+–Mn4+ ions coupled by strong short-range ferromagnetic (FM) double-exchange interactions in the paramagnetic state. The orbital ordering changes from FM to antiferromagnetic (AFM) type ∼190K (for x=0.4 and 0.5) and ∼180K (for x=0.45). The Néel Temperatures TN are 163K (for x=0.4 and 0.5) and 153K (for x=0.45). The temperature independence of ln (DI) double integrated intensity of the ESR resonance below 125K is ascribed to the existence of FM ordered microinhomogeneities embedded in the AFM ordered bulk sample. The TCO and TN values are found to be weakly dependent on the composition. The temperature dependence of ESR linewidth near TN has been analyzed in view of the spin-spin relaxation near magnetic critical points, as given by Seehra and Huber [AIP Conf. Proc. 24, 261 (1975)].