Magnetic susceptibilities and Mossbauer spectra of Sr2-xLaxFeO4-δ (0 ≤ x ≤ 0.5)

Solid solutions Sa(2-x)La(x)FeO(4-delta) (0 less than or equal to x less than or equal to 0.5) with the K2NiF4-type structure have been prepared, and their magnetic susceptibilities have been measured in the temperature range between 4.2 and 300 K. Substitution of the La ion for the Sr site considerably weakens the antiferromagnetic transition of Sr2FeO4, and it finally disappears in Sr1.6La0.4FeO4-delta. Below the magnetic transition temperatures, magnetic susceptibilities measured under zero-field cooled and field cooled conditions indicate the formation of a spin-glass state. Mossbauer spectra for Sr1.9La0.1FeO4-delta at room temperature and at 9 K have been measured, and the spectra at 9 K show the presence of magnetic hyperfine interaction of Fe4+ ions; there is no charge disproportionation of Fe4+ --> Fe3+ + Fe5+, even below the magnetic transition temperature. (C) 1999 Academic Press.