Ferromagnetism, phase separation and ultrasharp magnetization multisteps below 40 K in the ordered '112' cobaltites EuBaCo1.92M0.08O5.5−δ (M=Zn,Cu )

The study of the “112” ordered oxygen-deficient perovskites EuBaCo2O5.43, EuBaCo1.92Zn0.08O5.45, and EuBaCo1.92Cu0.08O5.40 evidences a magnetic transition at 40 K which may be due to the ordering of europium moments. Below 40 K, one observes phase separation that consists of superparamagnetic droplets and ferromagnetic (FM) regions embedded in an antiferromagnetic matrix. The existence of two sorts of crystallographic sites for cobalt, and its trivalent state, suggest that these phenomena correspond to ferromagnetism induced by the presence of intermediate spin Co3+ species. Moreover, the magnetization hysteresis loops of the Zn- and Cu-doped phases exhibit ultrasharp magnetization multisteps, which are interpreted by the pinning effect of Zn2+ and Cu2+ cations at the narrow domain walls of the FM phase.