Coexistence of ferromagnetic and antiferromagnetic orders in Ba-doped cobalt perovskites studied by neutron scattering*

Cobalt-containing oxide compounds have attracted a great deal of interest in recent years due to the variety of magnetic and electrical properties. We performed single crystal neutron diffraction on 6T2 at~the~LLB in France and~the~HB3A four-circle diffractometor at~the~HFIR of ORNL. The Ba-doped cobalt perovskite (La$_{0.8}$Ba$_{0.2}$CoO$_{3})$ crystal was measured in the temperature range of 2-250 K. At temperature $T<$ 200 K, a set of ferromagnetic peaks ($k_{1}$ = 0) onsets and then antiferromagnetic peaks with $k_{2}$* = (1/2 0 1/2) and (0 0 3/2) join in at $T<$ 100 K. Both ferromagnetic and antiferromagnetic peaks saturate at $T\approx $ 40 K. By refining the peaks collected for $k_{1}$ and $k_{2}$ sets, magnetic structures were determined.