MAGNETIC AND ORBITAL ORDERS COUPLED TO NEGATIVE THERMAL EXPANSION IN MOTT INSULATORS, CA2RU1-XMXO4 (M = 3D TRANSITION METAL ION)
Year of Publication
Doctor of Philosophy (PhD)
Arts and Sciences
Physics and Astronomy
Dr. Gang Cao
Ca2RuO4 is a structurally-driven Mott insulator with a metal-insulator (MI) transition at TMI = 357K, followed by a well-separated antiferromagnetic order at TN = 110 K. Slightly substituting Ru with a 3d transition metal ion M effectively shifts TMI and induces exotic magnetic behavior below TN. Moreover, M doping for Ru produces negative thermal expansion in Ca2Ru1-xMxO4 (M = Cr, Mn, Fe or Cu); the lattice volume expands on cooling with a total volume expansion ratio reaching as high as 1%. The onset of the negative thermal expansion closely tracks TMI and TN, sharply contrasting classic negative thermal expansion that shows no relevance to electronic properties. In addition, the observed negative thermal expansion occurs near room temperature and extends over a wide temperature interval. These findings underscores new physics driven by a complex interplay between orbital, spin and lattice degrees of freedom. These materials constitute a new class of Negative Thermal Expansion (NTE) materials with novel electronic and magnetic functions.
Qi, Tongfei, "MAGNETIC AND ORBITAL ORDERS COUPLED TO NEGATIVE THERMAL EXPANSION IN MOTT INSULATORS, CA2RU1-XMXO4 (M = 3D TRANSITION METAL ION)" (2012). Theses and Dissertations--Physics and Astronomy. 6.