Meissner superconductivity in itinerant ferromagnets

TL;DR

This paper reviews how ferromagnetism and unconventional spin-triplet superconductivity coexist in itinerant ferromagnets, emphasizing the role of spontaneous magnetization and phase stability within a Ginzburg-Landau framework.

Contribution

It introduces a quasi-phenomenological Ginzburg-Landau theory to describe the coexistence phase, analyzing phase stability and transition orders based on Landau parameters.

Findings

The coexistence phase is stable and triggered by spontaneous magnetization.

Phase transitions can be first or second order depending on the material.

The phase diagram is influenced by Cooper pair and crystal anisotropy.

Abstract

Recent results about the coexistence of ferromagnetism and unconventional superconductivity with spin-triplet Cooper pairing are reviewed on the basis of the quasi-phenomenological Ginzburg-Landau theory. The superconductivity in the mixed phase of coexistence of ferromagnetism and unconventional superconductivity is triggered by the spontaneous magnetization. The mixed phase is stable whereas the other superconducting phases that usually exist in unconventional superconductors are either unstable or metastable at relatively low temperatures in a quite narrow domain of the phase diagram and the stability properties are determined by the particular values of Landau parameters. The phase transitions from the normal phase to the phase of coexistence is of first order while the phase transition from the ferromagnetic phase to the coexistence phase can be either of first or second order depending on the concrete substance. The Cooper pair and crystal anisotropy are relevant to a more precise outline of the phase diagram shape and reduce the degeneration of the ground states of the system. The results are discussed in view of application to itinerant ferromagnetic compounds as UGe2, ZrZn2, URhGe.