Dielectric and magnetic properties of Fe and Ti based perovskite oxides

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The present PhD thesis deals with extensive investigation of magnetic and dielectric properties of (1) YFe1-xMnxO3 (x = 0 to 0.3), (2) Bi1-xSmxFeO3 (x = 0 to 0.3), (3) PbTi1-xFexO3 (x = 0 to 0.3) and (4) BaTi1-xFexO3 (x = 0 to 0.3) samples. Study of complex impedance spectra, dielectric constant and ac electrical conductivity of YFe1-xMnxO3 (x = 0 – 0.3) compounds elucidates the role played by both grains and grain boundaries in shaping the dielectric relaxation. The relaxation is attributed to the short-range movement of oxygen vacancies. The Nyquist plots of complex impedance were analyzed by fitting them to an equivalent electrical circuit. This circuit contains three parts connected in series: first one is the electrode resistance (RE); second one is the parallel combination of resistance and capacitance of grains (RG ,CG) and the third one is the parallel combination of resistance and constant phase element of grain boundaries (RGB, QGB). Mn substitution is found to decrease the Néel temperature from 646 K to 428 K and induce spin reorientation transition at low temperature from 4 (AxFyGz) to 1 (GxCyAz) spin configuration. The spin reorientation transition temperature is found to increase from 81 K for x = 0.1 to 295 K for x = 0.3. These samples exhibit interesting exchange bias behavior above room temperature with a maximum exchange bias field of 1.2 kOe at 413 K.
Supervisors: S. Ravi and A. Perumal