We have measured magnetic susceptibility and resistivity of
Sr1−x​Yx​CoO3−δ​ (x= 0.1, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3,
and 0.4), and have found that Sr1−x​Yx​CoO3−δ​ is a room
temperature ferromagnet with a Curie temperature of 335 K in a narrow
compositional range of 0.2 ≤x≤ 0.25. This is the highest transition
temperature among perovskite Co oxides. The saturation magnetization for x=
0.225 is 0.25 μB​/Co at 10 K, which implies that the observed
ferromagnetism is a bulk effect. We attribute this ferromagnetism to a peculiar
Sr/Y ordering.Comment: 5 pages, 4 figure