A thermodynamic framework for a system with itinerant-electron magnetism

Thermodynamic fluctuation among many electronic states in systems with 'itinerant-electron' magnetism is addressed with a first-principles formulation of the Helmholtz energy. The Ce gamma-alpha phase transition is used as an illustrative case. The k(B) ln(2J + 1) form for the magnetic entropy that is commonly found in the literature is replaced with an expression that is derived from configurational fluctuations among nonmagnetic, ferromagnetic, and antiferromagnetic electronic states. Predicted first- and second-order magnetic phase transitions are in close accord with experiment. The mixture of states leads to a Schottky anomaly in the Ce specific heat.