Thermodynamic fluctuations in magnetic states: Fe₃Pt as a prototype

Abstract

To understand the Invar anomalies, such as negative thermal expansion and spontaneous magnetization, we have applied our recently developed thermodynamic framework for a system with itinerant-electron magnetism to the ordered Fe₃Pt. The framework has coherently predicted the finite temperature intermixing between the fully ferromagnetic (FM) configuration and the spin-flipping configurations (SFCs). We have also discovered a tri-critical point at which a high-temperature second-order phase transition, between the fully ordered FM phase and the paramagnetic phase which is disordered due to SFCs, becomes first order at low temperatures.

Keywords:

• magnetic phase transition
• thermal expansion
• first-principles calculations
• Invar

Acknowledgements

We thank Mr. J.E. Saal for facilitating valuable discussions. This study was funded by the Office of Naval Research (ONR) under Contract No. N0014-07-1-0638, the National Science Foundation (NSF) through Grant No. DMR-0510180, and DOE Basic Sciences under Grant No. DOE DE-FG02-07ER46417 (Yi Wang and Chen), and in part supported by instrumentation funded by the National Science Foundation through grant OCI-0821527. Calculations were also conducted at the LION clusters at the Pennsylvania State University and at the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under Contract No. DE-AC02-05CH11231. This study was also supported in part by a grant of HPC resources from the Arctic Region Supercomputing Center at the University of Alaska Fairbanks as part of the Department of Defense High Performance Computing Modernization Program.