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

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.

7 pages, 7 figures, 1 table