Multiferroic magnetoelectric materials: Ferroelectricity induced by magnetic order and controlled by magnetic fields and pressure.
Bernd Lorenz
Texas Center for Superconductivity, University of Houston, Houston, TX
Date: June 15, 2007, Time: 3:30 pm, Location: W122-D3 Engineering Building 1, The University of Houston
Abstract:
Multiferroic magnetoelectric compounds exhibiting the coexistence of magnetic and ferroelectric orders have attracted attention because of the wealth of fundamental physical phenomena observed in these compounds and their implications on future applications as magnetoelectric memory or sensor elements. Of particular interest is a subgroup of magnetoelectrics characterized by improper ferroelectricity induced by magnetic orders. These materials usually undergo a sequence of magnetic phase transitions from paramagnetic to various antiferromagnetic phases with incommensurate or commensurate spin modulations in collinear or non-collinear magnetic structures. Typical examples are the rare earth manganites, RMnO 3 (R=Tb, Dy, Gd) and RMn 2O 5 (R=rare earth, Y), and other frustrated spin compounds such as Ni 3V 2O 8 and WMnO 4.
I will give a brief overview of the topic and discuss the magnetic origin of the ferroelectricity in multiferroics as well as novel physical effects observed in some of these compounds, including the giant magneto-dielectric response, the control of polarization by magnetic fields and pressure, and the experimental observation of a new fundamental excitation, electromagnons.
