Characterization of magnetic phase in yttrium-doped polycrystalline La1−x−yYyCaxMnO3 with x=0.05,0.33 and y=0.07 using dielectric and optical parameters

The dielectric permittivity of yttrium-doped polycrystalline samples La1−x−yYyCaxMnO3 with x=0.05,0.33 and y=0.07 has been measured at frequencies f from 20Hz to 2MHz and at temperatures T from 80K to 350K. These samples were prepared in the form of bulk polycrystals(ceramics) by solid state reaction method and characterized by X-ray diffraction technique. With the decrease in temperature, this system exhibits a phase transition from paramagnetic insulating to ferromagnetic metallic at a temperature TMI=225K for x=0.05 and at 170K for x=0.33. In this report, it is shown that such phase transition can be characterized by the exponents obtained from the scaling analysis of the variation of the real and the imaginary part of the dielectric permittivity ϵ1 and ϵ2 and the loss factor tanδ as a function of frequency and temperature. Results are analyzed systematically from the existing theoretical models and the scaling formalism.