Nearly Ferromagnetic Superconductors

TL;DR

This paper explores how ferromagnetic fluctuations influence superconducting properties near magnetic instability, revealing enhanced flux expulsion and altered critical parameters, with implications for understanding MgCNi microfibers.

Contribution

It introduces a generalized Ginzburg-Landau theory to analyze superconductors near ferromagnetic criticality, highlighting effects on magnetic and transport properties.

Findings

Magnetic flux expulsion increases with higher magnetic susceptibility.

Critical current exhibits a temperature exponent of approximately 2.

Ferromagnetic fluctuations significantly affect penetration depth and critical fields.

Abstract

The electromagnetic properties of superconductors near a ferromagnetic instability are investigated by means of a generalized Ginzburg-Landau theory. It is found that the magnetic flux expulsion capability of the superconductor gets stronger, in a well-defined sense, as the normal-state magnetic susceptibility increases. The temperature dependencies of the London penetration depth, the critical fields, and the critical current are all strongly affected by ferromagnetic fluctuations. In particular, for the critical current we find a temperature exponent alpha ~ 2 over an appreciable temperature range. The extent to which proximity to magnetic criticality may be a viable explanation for recent observations in MgCNi microfibers, which find alpha ~ 2, is discussed.