Magnetic and polar properties of some geometrically frustrated transition metal oxides

Abstract

Recently there has been a surge of research interest in the magnetoelectric multiferroics where magnetic and polar orders co exist Intense study of magnetoelectric coupling inseveral materials has shed light on the different possible scenarios of combining magnetismand ferroelectricity in a single phase material The discovery of type II multiferroics wherethe electric polarization is induced by a specific type of non collinear magnetic order ing has brought rapid growth in the research area of magnetelectric multiferroic Themagnetic order in geometrically frustrated magnets are often nontrivial and has been afertile playground for exploring magnetoelectric coupling In this thesis we aim to studygeometrically frustrated transition metal oxides for designing new magnetoelectric mul tiferroic materials and to study their physical properties Chapter 1 gives a brief introduction and evolution of the research area of magnetoelectricmultiferroics The issues associated with the coexistence of magnetism and ferroelectricityare highlighted Typically multiferroics are broadly classified in two categories namelytype I and type II In a type I multiferroic the magnetism and ferroelectricity occur fromdifferent origins and results in a weak coupling between the order parameters On theother hand for a type II multiferroic various type of commensurate incommensurate spinconfigurations break spatial inversion symmetry and provide a strong coupling betweenthe order parameters Possible mechanisms of inducing ferroelectricty and magnetismin both type I and II multiferroics are described in details Different theoretical modelsare qualitatively described and their experimental realization also is presented Finally technological applications of these materials are highlighted and the motivation and thescope of the thesis is presented Chapter 2 describes the following measurement facil newline newline