MAGNETIC AND ORBITAL ORDERS COUPLED TO NEGATIVE THERMAL EXPANSION IN MOTT INSULATORS, CA2RU1-XMXO4 (M = 3D TRANSITION METAL ION)

Author

Tongfei Qi, University of KentuckyFollow

Date Available

12-7-2012

Year of Publication

2012

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Physics and Astronomy

First Advisor

Dr. Gang Cao

Abstract

Ca₂RuO₄ is a structurally-driven Mott insulator with a metal-insulator (MI) transition at T_MI = 357K, followed by a well-separated antiferromagnetic order at T_N = 110 K. Slightly substituting Ru with a 3d transition metal ion M effectively shifts T_MI and induces exotic magnetic behavior below T_N. Moreover, M doping for Ru produces negative thermal expansion in Ca₂Ru_1-xM_xO₄ (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 T_MI and T_N, 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.

Recommended Citation

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.
https://uknowledge.uky.edu/physastron_etds/6