MAGNETO-VOLUME EFFECTS IN GAMMA-FE ULTRATHIN FILMS AND SMALL PARTICLES

Experimental results from 57Fe Mössbauer-effect investigations on epitaxial, γ-Fe ultrathin films and on γ-Fe precipitates are presented. Depending on the preparation conditions, low-moment anti-ferromagnetic Fe or high-moment ferromagnetic Fe is observed in fcc-Fe (0 0 1) films on Cu (0 0 1), and high-moment Fe in fcc-Fe (0 0 1) films on Cu3Au (0 0 1). Isomer-shift values suggest that this behavior is related to different lattice strains. The saturation hyperfine-field of antiferromagnetic coherent γ-Fe precipitates in a Cu100-xAlx matrix (0≤x≤14) was found to increase remarkably with increasing x, i.e., rising lattice expansion of the matrix. For γ-Fe precipitates in Cu, the magnetic transition temperature and the saturation hyperfine-field show an anomalous increase above a critical particle size indicating a suggested structural phase transition. Very small precipitates show superparamagnetism. © 1989.