DC-magnetron sputtered CoNiTa for high density longitudinal recording

Ternary cobalt alloy thin films were sputtered in a DC magnetron system. The alloys investigated consisted of (Co₇₅-Ni₂₅ )_1-xTa_x where x was varied from 0 to 20 at.%. The magnetic properties and microstructure of these films prepared with RF substrate bias as a function of composition, film thickness, Cr underlayer thickness, and temperature are reported. Tantalum additions to the CoNi result in a 100 to 200 Oe increase in coercive force depending upon the film thickness. The CoNiTa system approaches the superparamagnetic state at a thickness greater than for the CoNi system. The grain size of the CoNiTa is somewhat smaller than that of CoNi at similar thickness values. The increase in coercive force and decrease in S* associated with small Ta additions to CoNi films can be explained on the basis of Ta segregation to grain boundaries decreasing the exchange interaction and modifying the grain size