Phase Transitions in Novel Magnetic and Superconducting Compounds

Dr. John J. Neumeier
Department of Physics
Montana State University

Second-order phase transitions occur at a critical temperature Tc whereby the correlation length diverges. This indicates a scale-free phenomenon, where the new phase is a macroscopic entity originating from interactions occurring on a microscopic scale. Thermodynamic quantities such as the heat capacity and the thermal expansion coefficient also diverge at Tc. In the case of thermal expansion, the length changes associated with phase transitions are often only 1 to 10 angstroms within a few centigrade of Tc. As a result, obtaining useful thermal expansion data is a major challenge for experimental physicists. In this presentation, the physics of phase transitions will be highlighted, some recent advances in the measurement of thermal expansion will be presented, and examples of unique phase transitions will be given.