Investigations of Magnetic and Structural Properties of Rare Earth Substituted NdCrO3

Abstract

This thesis comprises magnetic and structural studies of substituted NdCrO3 compounds. The prepared samples exhibit high quality and their magnetic properties yield remarkable outcomes. The first work incorporates the synthesis of polycrystalline Nd1-xEuxCrO3 (x = 0.0-1.0) samples. The dc magnetization measurements show decreased antiferromagnetic transition temperature (TN) and spin-reorientation transition (TSR) with Eu substitution. The exchange bias (EB) effect is observed and the EB field decreases with increasing Eu content. The non-monotonic behavior of the EB field around T* ~ 90 K between the TN ~ 225 K and TSR ~ 35 K is observed for low substitution. The strong spin-phonon coupling for x = 0.0-0.20 samples is described via the evolution of Raman modes in 80-300 K temperature range. Importantly, the T* found from the non-monotonicity of the EB is imprinted with the additional phonon anomaly. The magnetoelastic coupling was explored by the variation of structural parameters in 3-300 K temperature range. The electron density distribution using the maximum entropy method around T* is studied. The study emphasizes lattice modulations near T* between TN and TSR for the first time in pure and substituted NdCrO3 by exploring spin-phonon induced exchange bias and magneto-structural imprints. The second work involves the investigations of Nd1-xPrxCrO3 (x = 0.0-0.30) samples. In contrast to Eu, here the substituent Pr is magnetic with larger ion size. The significant magnetization value with slightly increased TN and vanishing of TSR is observed. The Griffiths-like phase is seen for substituted samples. Compared to Eu substitution, here the larger value of EB field is achieved. The behavior of EB field below and above TSR with Pr substitution displayed interesting trends linked with structural parameters. These findings highlight the interplay of spin reorientation and EB in Nd1-xPrxCrO3 compounds. The last work is dedicated to the study of Nd1-xCexCrO3 (x = 0.0-0.175) compounds for the first time. The presence of mixed Ce valency on the Nd-site and its influence on NdCrO3 are discussed. The TN and TSR exist for all the samples. For the first time, a demonstration to obtain different magnitudes of magnetization at same applied field in opposite directions revealing different magnetic states is presented. Overall, the discovery of the spin-phonon induced exchange bias effect, structural reorientations, and magnetic states in compounds of Nd1-xRxCrO3 (R = Eu, Pr, and Ce) are witnessed. This thesis shows the magnetic transition can be coupled to crystalline lattice modulations near liquid nitrogen temperatures for potential applications as multifunctional material.