Electron Spin Resonance and Magnetization Studies of Bi-Rich La-Manganites

In this paper, the temperature-dependent electron spin resonance and magnetization (M) studies of La_0.7-xBi_xCa_0.3MnO₃ (x = 0, 0.35, 0.42, 0.56, and 0.63) manganites synthesized by the sol-gel method are reported. In all the samples, the coexistence of paramagnetic and ferromagnetic phases over a wide range of temperature is observed. The estimated Curie temperature (T_C), the Curie-Weiss temperature (θ_C), and the temperature at which linewidth (ΔH) becomes minimum (T_min) decrease with the increase in the Bi content. The decreasing trend of these parameters is discussed in view of the difference in the ionic radii of La³⁺ and Bi³⁺ and the variations in 6s² lone pair character of Bi³⁺ ions with the increase in the Bi content. The evolution of various types of magnetic interactions as a function of temperature and Bi content is discussed.