ANOMALOUS ANISOTROPY OF REENTRANT NI77MN23 FILM

Re-entrant polycrystalline Ni77Mn23 films, 600 Angstrom thick, grown o n a quartz substrate by using an electron beam evaporation technique, have been investigated. A spin-wave resonance (SWR) technique has been used to study the magnetic properties of the films. The SWR spectra e xhibit highly anisotropic behaviour with respect to the film normal. W hen the sample is rotated around the film normal in a fixed applied fi eld, both the resonance fields and the line-shapes are changed. This u nexpected behaviour - for a polycrystalline film - has been attributed to a growth-induced geometric (oblique) anisotropy. The SWR spectra h ave been successfully analysed by using this oblique anisotropy term i n addition to usual magnetocrystalline effective bulk, surface, and un idirectional anisotropy terms in the magnetic free energy. A substanti al and temperature-dependent growth-induced geometric anisotropy has b een obtained, beside the usual bulk and surface anisotropies. A strong correlation between the surface and oblique anisotropy has been found . This correlation has been attributed to a manifestation of the influ ence of easy-plane surface anisotropy along the fibre axes of individu al grains on the effective magnetic anisotropy energy.