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 T
s
ranging from 25 to 400°C, and their magnetic properties were investigated in connection with their micro-structure. H
c
was found to increase with increasing T
s
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 T
s
, 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, H
k
^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.