Tuning of Spin Reorientation and Compensation Transitions in Ferrites

Abstract

Ferrites have attracted the attention of scientists and engineers in the last few years because of a combination of ferrimagnetic and insulating character. This makes them suitable for high frequency devices in telecommunication and radar systems. The subsets of orthoferrites and spinel ferrites form the focus in this thesis. Magnetic interactions between 4f and 3d electrons of rare earth and transition metal based perovskite oxides give rise to several exciting properties, such as magnetoelectric effect, multiferroicity, spin-reorientation transition, magnetic compensation, magnetization reversal, and spin switching. Perovskite structure of orthoferrites allows a great deal of flexibility for doping in the A and B sites. By choosing a suitable dopant with optimum concentration, many properties of the parent compound can be tuned. We were motivated to raise the spin reorientation transition temperature of RFeO3 to as near as the room temperature by doping either sites. In this study, several interesting phenomena of doped orthoferrites will be discussed. Alongside, multifunctional spinel ferrites offering novel electrical and magnetic properties are explored. Their structural and magnetic properties were tuned by varying the cation distribution which has an influence on many magnetic properties and magnetic compensation phenomena. The work presented in this thesis is broadly divided into three parts. In the first part, B-site doping (50% Cr) and its effect on the magnetic properties of orthoferrites have been detailed, especially changes in the spin reorientation transition temperature of TbFeO3 (TbFe0.5Cr0.5O3). A clear evidence of Griffiths phase was observed which was presumably due to short range spin fluctuations. This was later confirmed from the results of neutron diffraction and thermal conductivity measurement. Further, a signature of spin-phonon coupling was observed in the Raman spectroscopy data...