Magnetic properties and anisotropy of CoCr thin films for perpendicular recording

CoCr thin films, 50 Å to 1 μm thick, have been rf sputtered onto a number of different substrates. These films have been studied for their nucleation, microstructure, magnetic properties, and anisotropy. It has been observed that at lower thicknesses, the grains are extremely small (200 Å at 0.1 μm) but cover the entire substrate surface quite uniformly. Below the thickness of 100 Å, the coercivity Hc approaches zero very rapidly and the film approaches superparamagnetic state. As the film thickness is increased, the grains get larger (800 Å at 1 μm) and the coercivity of the film increases. The Δθ50 value for the (0002) x-ray peak reached 2°. The grain size clearly dominates the coercivity of these films. The effective anisotropy constants increased from 1.31 to 3.16×105 ergs/cm3 for the above thickness range. Estimates of the magnetocrystalline anisotropy field are determined from a uniform thin-film model and a model that accounts for the columnar grains. When the circular magnetic columns are in contact, the shape anisotropy field is 5% lower than the uniform thin-film approximation. When the magnetic radius is 80% of the grain radius, then the shape anisotropy field is 34% lower.