Superconductivity and Field-Induced Magnetism in SrFe_1.75Co_0.25As_2

TL;DR

This study investigates the superconducting and magnetic properties of SrFe_1.75Co_0.25As_2, revealing two-gap superconductivity and field-induced magnetism using muon-spin rotation techniques.

Contribution

It provides new insights into the coexistence of superconductivity and field-induced magnetism in SrFe_1.75Co_0.25As_2, highlighting the presence of two-gap behavior and unusual internal field dynamics.

Findings

Presence of two superconducting gaps with specific gap ratios

Penetration depth anisotropy increases at low temperatures

External magnetic field induces a magnetic order throughout the sample

Abstract

Using muon-spin rotation, we studied the in-plane (\lambda_ab) and the out of plane (\lambda_c) magnetic field penetration depth in SrFe_1.75Co_0.25As_2 (T_c=13.3 K). Both \lambda_ab(T) and \lambda_c(T) are consistent with the presence of two superconducting gaps with the gap to T_c ratios 2\Delta/k_BT_c=7.2 and 2.7. The penetration depth anisotropy \gamma_\lambda=\lambda_c/\lambda_ab increases from \gamma_\lambda=2.1 at T_c to 2.7 at 1.6 K. The mean internal field in the superconducting state increases with decreasing temperature, just opposite to the diamagnetic response seen in magnetization experiments. This unusual behavior suggests that the external field induces a magnetic order which is maintained throughout the whole sample volume.