Frustrated magnetism and cooperative phase transitions in spinels

1Department of Physics, University of Virginia, Charlottesville, VA 22904, USA Advanced Institute for Materials Research, Tohoku University, Katahira, Sendai 980-8577, Japan 3Department of Advanced Materials, The University of Tokyo, Kashiwa, Chiba 277-8561, Japan 4Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 5The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan 6Department of Physics, Waseda University, Tokyo 169-8050, Japan 7Department of Physics, Korea University, Seoul 136-701, Korea HANARO Center, Korea Atomic Energy Research Institute, Daejeon, Korea 9Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA 10Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218. USA