Exploring the Physics and Application of biphasic La2NiMnO6 based Double Perovskites

Abstract

In the search of an alternative magnetoelectric material, La2NiMnO6(LNM) is a potential prototype due to its near room temperature ferromagnetic insulating nature, collosal magnetodi-electricity & magnetoresistance. The biphasic composition is more interesting to study because of the inherent intrinsic lattice strain. In the present thesis various physical properties such as structural, surface morphology, electrical, magnetic, magnetoimpedance, magnetoresistance and gas sensing properties of biphasic LNM and its derivatives are studied. Low temperature impedance, resistance, magnetoresistance, magnetoimpedance measurements are done in a Closed Cycle Refrigerator. Interfacing of instruments are done by LabView software. Biphasic LNM and its Cu2+ doped derivatives are prepared from the combustion method of synthesis. M-LNM is prepared by impregnating the LNM pellet. Rietveld renement of XRD data conrms the biphasic nature of samples with varying degrees of R 􀀀 3c and Pbnm phases. Surface mor- phology study by FESEM show the size of the nanoparticles around 30nm. Strong correlation of dielectric relaxation with magnetic ordering is seen in LNM. Signature of Griths phase is seen in the magnetization data. Due to partial Cu2+ substitution, there is decrease in Curietemperature and saturation magnetization with enhancement of various antiferromagnetic interactions. The strength of Griths phase and intrinsic dielectric constant increases with Cu2+ substitution. Contrasting magneteimpedance behaviours comprising positive magnetoimpedance for LNM and negative magnetoimpedance for M{LNM is seen. Based on the conductance and magnetoresistance behaviour, the conduction mechanism is modelled as spin polarized tunnelling through insulating gap in LNM and through shunt resistances in M-LNM. Signature of inverse metamagnetic transition originating due to the dipolar eld of Pbnm phase acting on R 􀀀 3cphase is seen in magnetoresistance of M-LNM. Exploration of gas sensing property of LNM reveals maximum sensitive for Argon gas amongst N2, Argon & O2 . [brace not closed]