Magnetodielectric coupling in multiferroic transition metal oxides

The study of materials that show cross-coupling effects between magnetization and electrical polarization (thus dielectric constant), has become one of the most popular areas in the field of solid state physics since the discovery of large magnetoelectric coupling in TbMnO3 in 2003. The revival of research into materials that show this cross-coupling effect, namely, magnetoelectrics and multiferroics, coincided with the integration of ferroelectric thin films and new high-k dielectrics in Si technology starting in the 1990s. These materials in thin film form could allow the coupling of polarization P to magnetization M, which can be potentially exploited for multiple-state memory elements. However, utilizing multiferroics as new multistate memory elements is not yet possible since the magnetic (electric) fields necessary to switch the electric (magnetic) state of the materials are too high to be used in memory devices due to the weak cross-coupling effects. This thesis aims to understand magneto(di)electric coupling in transition metal oxides. We have measured the magnetodielectric response of different known as well as novel materials and studied the effects of the magnetic symmetry and the structural changes on the magneto(di)electric coupling. Our studies provide valuable insight into the fundamental mechanisms of the coupling, which is necessary to understand the interplay of phonons, magnetism and electrical dipoles