Study Of Magnetic And Transport Anomalies In Rare Earth Based Intermetallics And Oxides

Abstract

Abstract There has been a considerable interest in understanding the physical properties of the compounds containing rare-earths, not only from the angle of basic science but also considering growing application potential. Current trends in condensed matter area suggest that investigation of new materials in particular are important in this respect, as such studies often paved the way for new concepts and resultant applications. Keeping this in mind, some ternary compounds – less investigated in the literature – have been taken up for magnetic investigations, and also for exploring antibacterial studies. Such compounds for our studies are: Nd2RhSi3, Er2RhSi3, Ho4PtAl, Er4PtAl, and Dy4RhAl among metals and spin-chain insulators Tb2BaNiO5 and Tb2BaCoO5, in both bulk and nanoforms. There are structural features facilitating ‘geometrically frustrated magnetism’ – a current trend in magnetism - in the above-mentioned metallic compounds. While many novel features (revealing structure-property relation) in the magnetic behavior of these compounds are reported in this thesis, main highlights are: (i) Establishment of an exceptional magnetism of Nd2RhSi3. (ii) Establishment of antiferromagnetism at 5 K in Er2RhSi3, however, with concurrent cluster spin-glass features, attributable to partially disordered antiferromagnetism; 1/3 magnetization plateau – less known among metals – and corresponding magnetoresistance plateau are intriguing findings. (iii) Ho4PtAl and Er4PtAl exhibit a re-entrant cluster spin-glass behavior, with the onset of an antiferromagnetic ordering; isothermal entropy change is very large at the onset of magnetic order, making these compounds useful for magnetic refrigeration applications. Dy4RhAl exhibits spin-glass features which coexists with xxvii antiferromagnetic order (18 K); this magnetic behavior is interestingly different from that of Dy4PtAl, which is ferromagnetic. (iv) Pressure studies on the magnetic ordering temperatures of well-known ‘exotic’ multiferroic systems. Tb2BaNiO5 and Tb2BaCoO5 bring out how magnetism of localized 4f electrons behave in a complex fashion to the application of external and chemical pressures, influencing other coupled phenomena. (v) A reduction in particle to nanoform in Dy4RhAl, leads to the evolution of a Griffiths-phase like behavior (a novel concept in magnetism), suppressing antiferromagnetic order – a rare demonstration in magnetic metals. In other cases, the changes in magnetic properties in nanoform are subtle. This reinforces the fact that one needs to be cautious while employing nanoparticles for medicinal applications based on the properties of the bulk forms, though none of these compounds are efficacious in inhibition of bacterial and fungal growths. The studies serve as a classic study for exploration of such rare-earth intermetallic materials for medicinal applications.