CHARACTERIZATION OF THE ANISOTROPY BEHAVIOR OF DIFFERENT COBALT MODIFIED GAMMA-FE2O3

We have investigated Go-surface adsorbed iron oxide particles with constant cobalt content and varying penetration depth of the Co2+ ions by means of ferromagnetic resonance, transverse susceptibility and VSM measurements. For all surface modified particles we have found that beside shape anisotropy, uniaxial as well as multiaxial anisotropy contributions play an important role in the magnetic behaviour, depending on the distribution width of the adsorption layer. The multiaxial contribution increases with increasing distribution width, while the uniaxial contribution decreases. In the scope of our theoretical models, we have calculated the uniaxial anisotropy constants at room temperature to be K-u = 3.5 x 10(5) J/m(3) fora distribution width of 2.5 Angstrom and K-u = 1.1 x 10(5) J/m(3) for a distribution width of 6 Angstrom.