Magnetic susceptibilities and Mossbauer spectra of Sr2-xLaxFeO4-delta (0 <= x <= 0.5)

Solid solutions Sa(2-x)La(x)FeO(4-delta) (0 less than or equal to x less th an 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 consider ably weakens the antiferromagnetic transition of Sr2FeO4, and it finally di sappears in Sr1.6La0.4FeO4-delta. Below the magnetic transition temperature s, magnetic susceptibilities measured under zero-field cooled and field coo led conditions indicate the formation of a spin-glass state. Mossbauer spec tra for Sr1.9La0.1FeO4-delta at room temperature and at 9 K have been measu red, and the spectra at 9 K show the presence of magnetic hyperfine interac tion of Fe4+ ions; there is no charge disproportionation of Fe4+ --> Fe3+ Fe5+, even below the magnetic transition temperature. (C) 1999 Academic Pr ess.