ESR and magnetization studies of Fe₂O₃-Bi₂O₃-ZnO-PbO glasses

The Electron Spin Resonance (ESR) and Magnetization measurements were undertaken in the temperature range 5–323 K to understand the spin dynamics in a new glass system with composition (Fe₂O₃)_x (70 Bi₂O₃ 20 ZnO 10 PbO)_1-x (x = 5 and 10 mol%). At high temperatures the ESR spectra consists of a narrow resonance at g ∼ 2. As the temperature decreases a second resonance peak emerges at a temperature, T_f which is ∼ 203 K. With further decrease in temperature, the second resonance peak progressively shifts towards lower field values. The ESR data shows the formation of magnetic clusters. The temperature dependent magnetization data exhibits a spin glass-like transition and a superparamagnetic blocking at a temperature which increases with decrease in x value. The unique magnetic transition of the present glass system is attributed to an inhomogeneous distribution of magnetic moments in the glass. There exist dilute and concentrated regions of magnetic moments. The former is responsible for a spin glass-like transition and the latter for superparamagnetic behavior.