Mössbauer study of magnetism in an amorphous Fe40B60 sputtered film

Abstract

Mössbauer studies of amorphous iron/boron alloys have proved useful for understanding magnetic phenomena in structurally disordered systems. In iron-rich alloys the 57Fe Mössbauer spectra at T≪TC of both melt-quenched and sputtered materials consist of broadened magnetic hyperfine lines, indicative of structural distortions in the compounds Fe2B and Fe3B. The spectra of sputtered films with approximately 50% Fe may be characterized by two qualitatively distinct Fe sites: (1) sites yielding a broadened magnetic hyperfine spectrum similar to the sharp spectrum of the compound FeB, and (2) sites having a zero (or very small) magnetic hyperfine field, evidenced by a slightly asymmetric, partially resolved, quadrupole doublet. In order to further examine the nature of these low field sites, a 40% Fe sputtered amorphous film was examined at 4.2 K in external magnetic fields up to 8.0 T. Interpretation is difficult, partly because the magnetic and quadrupole interactions are of comparable magnitude and partly because of the distributed nature of the hyperfine parameters. A pure spin-glass phase was ruled out by a narrowing of the spectrum in a 2.0 T external magnetic field. Two components were identified in the external magnetic field spectra: (1) nonmagnetic (∼50%), and (2) magnetic, with unusual behavior that may be due to a low-moment, mixed ferromagnetic/spin-glass phase.