Electron Spin Resonance Studies of Bi1-xCaxMnO3(X ≥ 0.65)

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 (Delta H) and resonance field (H-r) values of the ESR signal have been used to get information about magnetic interactions. The charge ordering (T-CO), antiferromagnetic (AFM) ordering, i.e., Neel temperature (T-N) values are estimated within +/-3 K of experimental error for all the samples. The estimated T-CO 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 T-N 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> T-CO. 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 < T-CO.