IRG 2: Multifunctional Magnetic Oxides

IRG-2 is focused on the science and technology of magneto-electric (ME) coupling both in bulk multiferroic transition metal oxides and in thin film heterostructures. Multiferroics are materials that exhibit two kinds of ferroic order simultaneously. Ferroelectric and magnetic orders which can lead to a strong coupling between the respective properties of the material are of particular interest. There has been a dramatic resurgence of interest in these materials following the discovery of magnetic switching of the polarization state in several improper ferroelectric multiferroics as well as development of elastically coupled composite multiferroics. The ME effects have great potential for important new technological applications in sensor arrays, memory devices, and information processing.

The properties of intrinsic multiferroics are governed by time reversal symmetry (magnetism) and spatial inversion symmetry (ferroelectricity). The combination of these two symmetries appears to lead to a new conserved quantity for multiferroics - the toroidal moment. Magnetic, dielectric and optical measurements have suggested the conservation of the toroidal moment. This concept may improve our understanding of these novel materials.

The coupling between ferroelectric and magnetic order also implies a coupling between the low lying lattice and magnetic excitations – the phonons and magnons which normally interact only weakly. The result is magnons (normally only magnetic dipole active) with electric dipole activity and phonons (normally only electric dipole active) with magnetic activity. The electric dipole coupled magnons or “electromagnons” are the new excitations of multiferroics that produce low frequency dielectric response which enhances the static dielectric constant in the multiferroic phase. This is the origin of a giant magneto capacitance which is another type of magneto - electric coupling.

IRG-2 is a team of materials scientists and physicists that has established itself as one of the leading research groups in metal oxides. We are using state of the art growth techniques for synthesizing single crystals and atomically controlled thin film multilayers. A comprehensive range of characterization tools and advanced theoretical analysis are implemented to address the science and technology of multiferroics. For instance, the use of laser MBE and combinatorial synthesis allows controlled growth and rapid optimization of useful properties. Samples are characterized by TEM, EELS, RHEED, synchrotron x-ray diffraction, magneto-circular dichroism, transport, magnetic, magneto-optical, and non linear optical, neutron scattering, and velocity of sound measurements. Lorentz microscopy and low temperature magnetic force microscopy are currently being added to further enhance the arsenal of characterization techniques. The goal of this research group is to understand the fundamental processes in these materials and develop and test novel room-temperature device concepts for their exploitation in applications including ultrasensitive magnetic field sensor arrays and bi-tunable memory elements.