Complex vortex-antivortex dynamics in the magnetic superconductor EuFe2(As0.7P0.3)2

EuFe2(As1-xPx)2 hosts complex dynamical processes resulting from the interplay of its two electronic ground states, i.e., ferromagnetism and superconductivity. A detailed understanding of the observed dynamics is, however, still missing. In this sense, frequency-resolved experimental techniques can be crucial to disentangle the magnetic and/or superconducting origin of the phenomenology and to contribute to its modeling. Here, we report on the investigation of EuFe2(As0.7P0.3)2 based on muon-spin spectroscopy and ac magnetic susceptibility (χ) measurements. The dependence of the internal field at the muon site on temperature is indicative of ferromagnetic ordering for the Eu2+ 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 χ'' by means of both standard ac susceptibility and a technique based on a microwave coplanar waveguide resonator. In particular, we detect activated trends for several features in χ'' over frequencies spanning ten orders of magnitude. To explain our results, we propose a model for the complex dynamics of vortices and antivortices influenced by the underlying structure of magnetic Meissner domains based on the identification of intra and interdomain depinning processes.