Theory of Itinerant Ferromagnetic Superconductor

Abstract

Using an electron-phonon system, the problem of the competition between the superconductivity and the itinerant ferromagnetism is investigated. We calculate the free energy assuming the ferromagnetic and superconducting order and obtain the transition temperatures, the order parameters, and the specific heat. As a result, we show that only the successive transition, para normal→ferromagnetic→superconducting state on cooling, is possible for this system. This coincides with the transition which Y₉Co₇ shows.