Investigation of some 4d and 5d transition metal based Double Perovskites

Abstract

Iridium based Double Perovskites have been of keen interest in solid-state Physics due to the intricate interplay of fundamental interactions like on-site Coulombic force, electron bandwidth, crystal field energy, and spin-orbit coupling. The dynamics between these forces and electron degrees of freedom (charge, spin, and orbital) result in novel electronic and magnetic ground states. During this project, Double Perovskites; Ba2FeIrO6, Y2(Ni/Co)IrO6 are synthesized via solid-state route. Ba2FeIrO6 with Ir in 5+ oxidation state crystallizes in a hexagonal structure. Due to the similarity in ionic radii of two transition metal cations, it possesses high antisite disorder. This also reflects in its molar heat capacity measurement, which shows evidence of a glassy phase. Y2(Ni/Co)IrO6, on the other hand, has iridium in the 4+ oxidation state and crystallizes in monoclinic structure. The octahedral tilt occurring to compensate the small A cation size results in a high magnetic order temperature of 186K in Y2NiIrO6. The data obtained corroborate with the strong magneto-structural coupling observed in the Ln2NiIrO6 series. Molar heat capacity studies indicate the presence of glassy phase at low temperature. The development of an automated susceptometer for measuring linear and non-linear dielectric response has also been a part of the project. The design principles, as well as the calibration of the instrument using the first harmonic response of a standard dielectric sample KH2PO4 is described.