Induced surface anisotropy of amorphous iron-nickel alloys studied by ferromagnetic resonance and antiresonance

The thermally induced (by annealing) surface anisotropy (SA) is studied in ribbon-shaped iron-rich amorphous alloys (prepared by roller quenching method), mainly by the methods of ferromagnetic resonance and antiresonance at frequencies in the range 9-95 GHz, in external static magnetic fields oriented either in the plane of the ribbon or perpendicularly to the plane. The large difference between the ferromagnetic resonance and antiresonance penetration depths is pointed out. The magnetic homogeneity of the samples is checked. The induced surface anisotropy constant K-s amounts to several tenths of erg/cm(2), its symmetry is uniaxial with the easy axis oriented along the normal to the sample surface. The temperature dependence of K-s reveals a critical point around 400 K, above which K-s approximate to 0. The origin of SA lies most probably in occurrence of non-stoichiometric ferrimagnetic oxides, which arise in the annealing process in a few surface atomic planes of the sample and which interact with the bulk of the material. The magnetoelastic origin of the interaction is not probable.