Complex magnetism and structural phase transition in correlated oxide systems

Abstract

Perovskite and pyrochlore materials constitute a profoundly intriguing and extensively studied family owing to their diverse magnetic and structural properties. we thoroughly explored the structure and magnetism of the polycrystalline LaFe0.5Mn0.5O3 compound. The compound shows antiferromagnetic ordering at 276 K. Additionally, Griffiths Phase-like phenomenon was observed from 276 K to 314 K. At lower temperatures, the dominance of ferromagnetic interaction becomes noticeable, significantly influencing spontaneous magnetization (Ms). Next, a comprehensive exploration of the structural and magnetic characteristics of the 6H perovskite Ba3Nd0.5Gd0.5Ru2O9 has been done. This material showcases a layered structure with Ru2O9 dimers, highlighting a mixed oxidation state of Ru4+ and Ru5+. At room temperature (300 K), it crystallizes in a hexagonal structure with the P63/mmc space group and undergoes a structural phase transition to a monoclinic structure (C2/c) around 127.3 K as the temperature decreases. At 23.7 K, the compound undergoes a ferromagnetic transition. However, below this temperature, it exhibits a competition between ferromagnetic and antiferromagnetic behaviours, influenced by the presence of rare earth elements (Gd and Nd). An intriguing Griffiths phase-like behaviour is observed from 201 K to 23.7 K. Magnetocaloric study reveals an entropy change of 2.1508 JKg−1K−1 around the ferromagnetic transition at TC = 23.7 K. Then, we aim to delve into the specific structural attributes of Tb2Ti2O7 and shed light on its unique properties. Employing a thorough investigation that utilizes high-brilliance synchrotron X-ray diffraction. we meticulously examined the structural evolution of Tb2Ti2O7 under external pressure and temperature. Our findings conclusively confirm the occurrence of an isostructural phase transition beyond the pressure threshold of 10 GPa. This transition is marked by a distinctive signature in the variation of lattice parameters under pressure, inducing changes in mechanical properties.

Finally, we focus on single crystals of Sm1−xYxFeO3 (x = 0.3, 0.7) and their intriguing magnetic properties. Crystals were grown using an optical floating zone (OFZ) furnace with the zone refinement technique. Sm1−xYxFeO3 (x = 0.3, 0.7) crystals along different crystallographic axes confirmed a spin reorientation transition. At low temperatures below 15 K, various anomalies appear in Sm1−xYxFeO3 due to rare earth ordering. Exchange bias behaviour was observed at 5 K in all the samples.