Magnetism and superconductivity in Eu(Fe$_{1-x}$Ni$_{x}$)As$_2$ ($x$ = 0, 0.04)

TL;DR

This study investigates how Ni doping in Eu(Fe$_{1-x}$Ni$_{x}$)As$_2$ suppresses magnetic order and induces superconductivity at 17.5 K, revealing coexistence of magnetism and superconductivity in this material.

Contribution

It reports the emergence of superconductivity and coexistence with magnetic order in Ni-doped EuFeAs$_2$, providing new insights into the interplay between magnetism and superconductivity in 112-type ferroarsenides.

Findings

Ni doping suppresses SDW transition

Superconductivity appears at 17.5 K in doped sample

Magnetism coexists with superconductivity below 6.2 K

Abstract

We report Eu-local-spin magnetism and Ni-doping-induced superconductivity (SC) in a 112-type ferroarsenide system Eu(Fe$_{1-x}$Ni$_{x}$)As$_2$. The non-doped EuFeAs$_2$ exhibits two primary magnetic transitions at $\sim$100 and $\sim$ 40 K, probably associated with a spin-density-wave (SDW) transition and an antiferromagnetic ordering in the Fe and Eu sublattices, respectively. Two additional successive transitions possibly related to Eu-spin modulations appear at 15.5 and 6.5 K. For the Ni-doped sample with $x$ = 0.04, the SDW transition disappears, and SC emerges at $T_\mathrm{c}$ = 17.5 K. The Eu-spin ordering remains at around 40 K, followed by the possible reentrant magnetic modulations with enhanced spin canting. Consequently, SC coexists with a weak spontaneous magnetization below 6.2 K in Eu(Fe$_{0.96}$Ni$_{0.04}$)As$_2$, which provides a complementary playground for the study of the interplay between SC and magnetism.