The internal magnetic field in superconducting ferromagnets

TL;DR

This paper provides direct experimental evidence of the coexistence of ferromagnetic and superconducting orders in Ru-1222, revealing the interplay between domain structures and vorticity through nonlinear ac magnetic response measurements.

Contribution

It demonstrates the coexistence of ferromagnetism and superconductivity in high-$T_c$ ruthenocuprates via nonlinear magnetic response analysis.

Findings

Evidence of interplay between domain structure and vorticity.

Confirmation of coexistence of ferromagnetic and superconducting orders.

Dependence of magnetic response on cooling regimes.

Abstract

We have measured the nonlinear response to the ac magnetic field in the superconducting weak ferromagnet Ru-1222, at different regimes of sample cooling which provides unambiguous evidence of the interplay of the domain structure and the vorticity in the superconducting state. This is {\em direct} proof of coexistence of ferromagnetic and superconductive order parameters in high-$T_c$ ruthenocuprates.