Electron Spin Resonance Studies of Bi$_{1 - {\rm x}}$Ca$_{\rm x}$MnO$_{3}$(X $\geq$ 0.65)

Abstract

In this paper, we report the electron spin resonance (ESR) studies of Bi1-xCaxMnO3 (0.65 ≤ x ≤ 0.90) samples synthesized by sol-gel technique. From the temperature dependent ESR data, double integrated intensity (DI), linewidth (ΔH) and resonance field (Hr) values of the ESR signal have been used to get information about magnetic interactions. The charge ordering (TCO), antiferromagnetic (AFM) ordering, i.e., Neel temperature (TN) values are estimated within ±3 K of experimental error for all the samples. The estimated TCO values are 288, 302, 219, and 220 K for x = 0.65, 0.70, 0.75, and 0.80 samples, respectively. The charge ordered state is suppressed for samples with x = 0.85 and 0.90. The estimated TN values are 139, 128, 139, 132, 126, and 126 K for x = 0.65, 0.70, 0.75, 0.80, 0.85, and 0.90, respectively. For the samples with 0.65 ≤ x ≤ 0.80, the ferromagnetic (FM) interactions dominate in the temperature range T >; TCO. Whereas for x = 0.85 and 0.90 samples, the existence of AFM superexchange interactions and localized FM-AFM transition are evident. The FM and AFM correlations coexist in the temperature range TN <; T <; TCO.