Effects of Underlayer on Magnetic Properties of CoNiCr Thin Film Media Sputtered on Glass Substrates

CoNiCr/Cr films were sputtered onto polished glass at temperatures Ts ranging from 25 to 400°C, and their magnetic properties were investigated in connection with their micro-structure. Hc was found to increase with increasing Ts while sputtering GoNiCr/Cr films, which consisted mainly of an h.e.p. phase. Analytical transmission electron microscopy revealed that the underlayer Cr diffused into grain boundaries of the CoNiCr layer, and at higher Ts, into individual CoNiCr grains. Torque loss analyses were performed to determine the magnetic isolation among CoNiCr grains. The uniaxial magnetic anisotropy field for individual grains determined experimentally, Hk^grain (exp), was found to increase with increasing Ts. Metalographical change promoted magnetic isolation among h.e.p. CoNiCr grains, and as a result, the microscopic demagnetizing field in each CoNiCr grain increased. This conclusion is well supported by the experimental results of the torque loss analysis in this work.