Magnetism and superconductivity in single crystals $E{u}_{1-x}S{r}_{x}F{e}_{2-y}C{o}_{y}A{s}_2$

Abstract

We systematically studied the transport properties of single crystals of $E{u}_{1-x}S{r}_{x}F{e}_{2-y}$Co${}_{y}A{s}_2$. Co doping can suppress the spin-density wave (SDW) ordering and induces a superconducting transition, but a resistivity reentrance due to the antiferromagnetic ordering of $E{u}^{2+}$ spins is observed, indicating the competition between antiferromagnetism (AFM) and superconductivity. It is striking that the resistivity reentrance can be completely suppressed by external magnetic field (H) because a metamagnetic transition from antiferromagnetism to ferromagnetism for $E{u}^{2+}$ spins is induced by magnetic field. Superconductivity without resistivity reentrance shows up by partial substitution of Eu${}^{2+}$ with non-magnetic Sr${}^{2+}$ to completely destroy the AFM ordering of $E{u}^{2+}$ spins. These results suggest that the antiferromagnetism destroys the superconductivity, while the ferromagnetism can coexist with the superconductivity in the iron-based high-$T_c$ superconductors.

5 pages, 4 figures