Complex vortex-antivortex dynamics in the magnetic superconductor EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$

TL;DR

This study explores the complex vortex-antivortex dynamics in the magnetic superconductor EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ using muon-spin spectroscopy and ac susceptibility, revealing rich phenomenology linked to magnetic domains and vortex behavior.

Contribution

It introduces a combined experimental approach revealing detailed vortex-antivortex dynamics influenced by magnetic domains in EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$, a novel insight into magnetic superconductor behavior.

Findings

Ferromagnetic ordering of Eu$^{2+}$ moments confirmed.

Activated trends in susceptibility features over wide frequency range.

Complex vortex-antivortex dynamics influenced by magnetic domains observed.

Abstract

We report on the investigation of the magnetic superconductor EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ based on muon-spin spectroscopy and ac magnetic susceptibility ($\chi$) measurements. The dependence of the internal field at the muon site on temperature is indicative of a ferromagnetic ordering of Eu$^{2+}$ magnetic moments and only the conventional magnon scattering governs the longitudinal relaxation rate at low temperatures. At the same time, we observe a rich phenomenology for the imaginary component of the susceptibility $\chi^{\prime\prime}$ by means of both standard ac susceptibility and a novel technique based on a microwave coplanar waveguide resonator. In particular, we detect activated trends for several features in $\chi^{\prime\prime}$ over frequencies spanning ten orders of magnitude. We interpret our results in terms of the complex dynamics of vortices and antivortices influenced by the underlying structure of magnetic domains.