Varying Eu${}^{2+}$ magnetic order in EuFe${}_2$As${}_2$ by chemical pressure

Abstract

Among iron 122 pnictide superconductors, the EuFe${}_2$As${}_2$ series draws particular interest because, in addition to superconductivity or the long-range spin-density-wave order in the Fe subsystem, the localized Eu${}^{2+}$ magnetic moments order at low temperatures. Here we present a novel scheme of how the spins align in the Eu compounds when pressure varies the coupling; we explain magnetization measurements on EuFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$ single crystals as well as other observations of the Eu${}^{2+}$ ordering previously reported in literature. The magnetic moments of the Eu${}^{2+}$ ions are slightly canted even in the parent compound EuFe${}_2$As${}_2$, yielding a ferromagnetic contribution along the $c$-direction that becomes stronger with pressure. Reducing the interlayer distance even further, the antiferromagnetic coupling of the $ab$ planes finally turns ferromagnetic.

4 pages, 4 figures