ties of SrFe 1Ϫx Co x O 3 . Both SrFeO 3 (x ϭ 0) and SrCoO 3 SrFe 1؊x Co x O 3؊␦ (0 Յ x Յ 1, ␦ Յ 0.06) of the cubic perovskite (x ϭ 1) contain transition metals with high oxidation numtype was prepared by treating mixtures of grossly oxygen-defibers; Fe 4ϩ and Co 4ϩ , whose 3d levels are deep and close cient samples obtained at ambient pressure with an oxidizer, in energy to the oxygen 2p levels, have cubic perovskite KClO 4 , at 6 GPa and 873 K. The lattice parameters were structures in which metal-oxygen-metal interactions are determined by X-ray diffraction measurements and their magenhanced, and are rather good conductors with resistivities netic properties were characterized by measurements of magne-() on the order of 10 Ϫ1 ȁ 10 Ϫ4 ⍀ cm (3). We believe that tization and Mo ¨ssbauer spectroscopy. The ferromagnetic Curie the present system provides an opportunity to study how temperature has been found to be raised above 300 K for the electronic properties change as a function of d-electron 0.4 Յ x Յ 0.9 (340 K at x ؍ 0.6) by the high pressure treatment, density and oxygen content. The background is briefly and the composition dependence of saturation magnetization described below.
for x Ն 0.4 is consistent with a simple picture in which Fe 4؉ ions with 4 B and Co 4؉ ions with 1.8 B align their moments SrFeO 3 is an antiferromagnet with a Neel temperature ferromagnetically. The saturation magnetic hyperfine field, (T N ) of 134 K. The spin structure is of a screw type with which is 330 kOe for SrFeO 3 , decreases quickly at first (x Յ a wave vector along the ͗111͘ axis. Assuming Heisenberg-0.15) and then slowly to about 290 ȁ 300 kOe, or exponentially, type exchange interactions, Takeda et al. estimated the as Co content increases, suggesting that the Co substitution magnitude as J 1 ϭ 1.2 meV, J 2 ϭ Ϫ0.2 meV, and J 4 ϭ Ϫ0.3 tends to delocalize electrons of Fe parentage in a broadened meV from neutron paramagnetic scattering measurements, * band. SrFeO 3 , an antiferromagnet with a relatively low T N where J i stands for the interaction of an Fe ion with the of 134 K, and Sr 2 FeCoO 6 , a ferromagnet with a high T C of 340 ith nearest neighbors (4, 5). The coexistence of the ferro-K, seem to represent the two electronic phases switched from magnetic nearest-neighbor interaction and the considerone to the other at x ؍ 0.1 ȁ 0.15.