Temperature and magnetic field dependent magnetic properties and critical behavior of some electron doped rare earth manganites

Abstract

This thesis deals with the results of experimental investigation on temperature and newlinemagnetic field dependent magnetic properties and critical behavior of some electron doped newlinemanganites using experimental magnetization data. A series of polycrystalline electron-doped rare newlineearth manganites Ca0.85R0.15MnO3 (R = Dy, Sm, Nd) are synthesized and a systematic newlineinvestigation of structural properties, magnetic properties and critical behavior of these materials newlineis carried out. Structural parameters of all these samples are determined by analyzing newlinecorresponding x-ray diffraction profile based on Rietveld refinement method using the profile newlineanalysis program FULLPROF. For measuring magnetization both VSM magnetometer and newlineSQUID magnetometer have been used. Magnetic properties and critical behavior of these newlinecompounds are studied based on dc magnetization data. DC magnetizations have been measured newlinein both zero field cooled (ZFC) and Field cooled (FC) sequences . Critical behaviors of these newlinematerials are studied based on isothermal magnetization data using the techniques like Arrott plot, newlinemodified Arrott plot (MAP) method, Kouvel-Fisher method and critical isotherm analysis. All the newlinesynthesized materials exhibit almost same qualitative behavior but small variation of magnetic newlineproperties and critical behavior are observed with the variation of the substituting rare earth newlineelement. The effects of Griffiths phase and magnetic relaxation behavior on the magnetocaloric newlineeffect are studied. newlineTemperature and Magnetic field dependent magnetization properties of electron doped newlinepolycrystalline sample Ca0.85Dy0.15MnO3(CDMO) prepared by solid state reaction method have newlinebeen studied. The sample undergoes ferromagnetic to paramagnetic phase transition at about newline111K. From the study of magnetic properties in terms of Arrott plots it is observed that the phase newlinetransition is of 2nd order. newline