Ferromagnetic properties of SrFe1-xCoxO3 synthesized under high pressure

SrFe1-xCoxO3-delta (0 less than or equal to x less than or equal to 1, delta less than or equal to 0.06) of the cubic perovskite type was prepared by treating mixtures of grossly oxygen-deficient samples obtained at ambient pressure with an oxidizer, KClO4, at 6 GPa and 873 K. The lattice parameters were determined by X-ray diffraction measurements and their magnetic properties were characterized by measurements of magnetization and Mossbauer spectroscopy. The ferromagnetic Curie temperature has been found to be raised above 300 K for 0.4 less than or equal to x less than or equal to 0.9 (340 K at x = 0.6) by the high pressure treatment, and the composition dependence of saturation magnetization for x greater than or equal to 0.4 is consistent with a simple picture in which Fe4+ ions with 4 mu(B) and Co4+ ions with 1.8 mu(B) align their moments ferromagnetically, The saturation magnetic hyperfine field, which is 330 kOe for SrFeO3, decreases quickly at first (x less than or equal to 0.15) and then slowly to about 290 similar to 300 kOe, or exponentially, as Co content increases, suggesting that the Co substitution tends to delocalize electrons of Fe parentage in a broadened sigma* band. SrFeO3, an antiferromagnet with a relatively low T-N of 134 K, and Sr2FeCoO6, a ferromagnet with a high T-c of 340 K, seem to represent the two electronic phases switched from one to the other at x = 0.1 similar to 0.15. (C) 1996 Academic Press, Inc.