Magnetic properties and anisotropy of CoCr thin films for perpendicular recording (abstract)

Abstract

The magnetic properties, microstructure, and anisotropy of CoCr thin films have been studied using VSM, x-ray, torque magnetometer, and electron microscopy techniques. These films were grown on a number of different substrates including sapphire, glass, mica, Al, and Ni-P, by rf sputtering, in the thickness range 300 Å–1 μm. The microstructures dominate the magnetic properties of these films and the coercivity Hc continues to increase even up to the grain diameters of 1000 Å. The Δθ50 value for the (0002) x-ray peak reached 2°. For the sapphire the anisotropy field Hk is positive down to a film thickness of 500 Å. Effective anisotropy constants as measured by torque magnetometer increase from 1.31 to 3.16×10+5 erg/cm3 for film thicknesses ranging from 0.1 to 1 μm. We have estimated the magnetocrystalline anisotropy from the measured anisotropy values from the torque magnetometer. In calculating the shape anisotropy, this model accounts for magnetostatically interacting cylindrical columns as opposed to the simple uniform thin-film model. Since there is experimental evidence that Cr segregates towards the grain-boundary walls, a variety of models were used where the diameter of the grains were kept constant while the diameter of the magnetic parts of the grains were gradually reduced. When the magnetic columns are in contact, the shape anisotropy field Hs is 5% lower than the uniform thin film approximation. When the magnetic radius is 80% of the grain radius, then the Hs is 34% lower, but the magnetocrystalline anisotropy constant Ku is 7% higher.