Structural, dielectric and magnetic properties of La0.55Sr0.45MnO3 polycrystalline perovskite

Polycrystalline perovskite La0.55Sr0.45MnO3 has been prepared by the conventional solid-state reaction route using planetary ball milling technique. The structural properties have been investigated using XRD and SEM data. Rhombohedral structure with space group R-3c of the sample is confirmed by room temperature XRD investigation. Microstructure and chemical composition were determined by Scanning Electron Microscopy (SEM), which includes an energy dispersive X-ray diffractometer (EDX). The study of the dielectric properties of the sample reveals that La0.55Sr0.45MnO3 possesses a high dielectric constant at room temperature and at low frequencies. The real part of the dielectric constant epsilon' is also observed to be strongly dependent on the temperature and the best properties are found in the sample at room temperature for which epsilon' approximate to 10(4) up to f = 4x10(6) Hz. The dispersion of dielectric constants at low frequency is explained in the light of Maxwell-Wagner model. A pronounced increase in Capacitance C is observed from 273 K to 298 K and likely to be caused by the redistribution of ions due to the thermal agitation. The resistivity decreases with increasing temperature indicating that the sample has a semiconductor-like behavior. The constant value of mu' over a wide range of frequency indicates the compositional stability and the range of the suitability of the perovskite. A significant decrease of ac permeability has occurred around 298 K indicating a magnetic phase transition from ferromagnetic to paramagnetic state. Low temperature magnetization measurement reveals paramagnetic to ferromagnetic (FM) transition upon cooling at T-C = 244 K. But the FM state coexists with the residual canted AFM (anti-ferromagnetic) state rather than a pure FM state. Presence of external field H favors the FM phase which expands at the expense of the AFM phase. Thus M-H measurement reveals high saturation magnetization.