Distinguishing nanostructured Al-doped maghemite-like Fe2-yAlyO3 from spinel-like Fe3-yAlyO4

A. F. CABRERA; C. E. RODRÍGUEZ TORRES; S. J. STEWART

Hyperfine Interactions

Springer Nature

Año: 2024 vol. 245

We present an investigation of a nanostructured Fe-Al-O system with x = Al/Al + Fe ratiosof 0.17, 0.33 and 0.50, prepared by the autocombustion method. The main phase found inall samples is the cubic spinel phase. The inclusion of Al in the spinel structure resultedin a progressive decrease in both the cell parameter and the grain size, with the formerapproaching the cell parameter of maghemite rather than magnetite. Although the XRDpatterns match those reported for AlFe2O4, Mössbauer spectroscopy and magnetic measurementsallows us to determine that the formed spinel phase can be identified as Aldopedmaghemite-like Fe2-yAlyO3. The room temperature Mössbauer spectrum of samplex = 0.17 consists of magnetic components belonging to iron at the iron (III) oxide spinelsites, plus a central doublet. For higher Al content, the relative area of the magnetic componentsdecreases, and the spectra mainly consists of a Fe3+ broad doublet correspondingto superparamagnetic iron (III) oxide particles. The 13 K spectrum of x = 0.33 sample(nominally AlFe2O4) is mainly composed of magnetic sites belonging to blocked particlemoments of Al-doped maghemite-like particles. The magnetization loops are consistentwith a ferro/ferrimagnetic behaviour, whose saturation magnetization decreases with theincorporation of Al.