FERROMAGNETIC-RESONANCE STUDIES OF GRANULAR GIANT-MAGNETORESISTIVE MATERIALS

Ferromagnetic resonance (FMR) can reveal important information on the size and shape of the ferromagnetic particles which are dispersed in g ranular giant magnetoresistive (GMR) materials. We have investigated t he FMR spectra of three different types of granular GMR material, each with different properties: (1) melt-spun ribbons of Fe5Co15Cu80 and C o20Cu80, (2) thin films Of C020Cu80 produced by pulsed laser depositio n, and (3) a granular multilayer film of [Cu(50 angstrom)/Fe(10 angstr om) ] X 50. We interpret the linewidth of these materials in as simple a manner as possible, as a ''powder pattern'' of noninteracting ferro magnetic particles. The linewidth of the melt-spun ribbons is caused b y a completely random distribution of crystalline anisotropy axes. The linewidth of these samples is strongly dependent upon the annealing t emperature: the linewidth of the as-spun sample is 2.5 kOe (appropriat e for single-domain particles) while the linewidth of a melt-spun samp le annealed at 900-degrees-C for 15 min is 4.5 kOe (appropriate for la rger, multidomain particles). The linewidth of the granular multilayer is attributed to a restricted distribution of shape anisotropies, as expected from a discontinuous multilayer, and is only 0.98 kOe when th e applied magnetic field is in the plane of the film.