Ferromagnetic resonance of monodisperse Co particles

Two-dimensional arrays of monodisperse nanosized Co particles are prepared on carbon and glass substrates by a magnetophoretic deposition technique from colloidal suspensions. Transmission electron microscopy (TEM) reveals a complicated cubic crystalline structure of the particles and hexagonal ordering over several micrometers squared, if the colloidal suspension is dried in magnetic fields of up to 0.8 T. Angular-dependent ferromagnetic resonance (FMR) spectra of 4-, 5-, 9-, and 12-nm-diameter particles at 297 K show that the easy axis of magnetization is in plane and that only the 12 nm particles are measured below the blocking temperature estimated to be 656 K. The resonance linewidth is on the order of 0.1 T, indicating a much larger magnetic inhomogeneity of the particles than the small geometric and size distribution (< 10%) observed by TEM suggests. Characteristic differences of the FMR spectra for different substrates and deposition parameters are observed. (C) 2001 American Vacuum Society.