Wednesday, September 28, 2016
Transition metal oxides exhibit almost every physical state known including metallic conductivity, (high-temperature) superconductivity, colossal magnetoresistance, photoconductivity, ferroelectricity, and ferromagnetism. Key to both harnessing these exotic phases in device applications and further materials discovery is developing an atomic-resolution understanding of the structural, electronic and magnetic properties. Here I will show how analytical electron microscopy and spectroscopy, in conjunction with advanced thin film deposition, can be used to engineer new materials including a magnetoelectric multiferroic superlattice where ferroelectricity enhances magnetism at all relevant length scales. Starting with a single layer of a ferrimagnet with magnetic spin frustration, we impose sub-Angstrom ferroelectric rumpling to lower the spin frustration and boost the magnetic transition to above room-temperature. As motivated by atomic-resolution electron spectroscopy, we further engineer the ferroelectric domain architecture to move charge through the system to boost the magnetic moment. Our results demonstrate a design methodology for creating higher-temperature multiferroics by exploiting a combination of geometric frustration, polarization doping and epitaxial engineering.