Magnetoelectric and magneto-dielectric effects in multiferroic manganites

Ferroelectric and magnetic materials have been a time-honored subject of study and have lead to some of the most important technological advances to date. Magnetic ordering is governed by the exchange interaction of the electron spins, while ferroelectric ordering is governed by the off-center structural distortions in the lattice. These two seemingly unrelated phenomena can actually coexist in certain unusual materials, termed multiferroics. The understanding of this remarkable occurrence remains a scientific challenge. Despite the possible coexistence of ferroelectricity and magnetism, any profound interplay between them has been rarely observed. This fact has largely prevented the realization of devices with a previously unavailable functionality, which these multiferroics could make possible. Herein, I have explored several multiferroic materials, which show astonishing interplays between ferroelectricity and magnetism during the course of my dissertation. A number of new discoveries have been made in the multiferroic manganites. Especially, polarization reversal by magnetic field and colossal magneto-capacitance effect have been observed in ThMn2O5 and DyMn2O5, respectively.