Dependence of magnetic properties on magnetic layer thickness in SmCo/Cr films

SmCo/Cr films were prepared with the thickness of SmCo layer varying from 1 to 400 nm, and the dependence of the magnetic properties on SmCo layer thickness was studied. Atomic force microscopy (AFM) measurement revealed that both the Cr underlayer and SmCo/Cr films were very similar in surface morphology with the surface roughness (Ra) of about 6 nm for the SmCo layer thinner than 100 nm. The Cr underlayer contributes to generate small grain size and smooth surface for SmCo layer as well as to improve its magnetic properties. The maximum coercivity was about 3.3 kOe, and the squareness and the coercive squareness in the plane direction were about 0.91 and 0.97, respectively, when the SmCo layer thickness was 40 nm. The diameter of switching unit estimated by the magnetic switching volume was smaller than 30 nm, while AFM observations show a grain size of 50 nm or more. The magnetic properties and the microstructure of SmCo/Cr bilayer films promise to be suitable for high density recording media applications.