Dependence of magnetics, microstructures and recording properties on underlayer thickness in CoNiCr/Cr media

The effect of Cr underlayer thickness on the magnetic, microstructural, and recording properties of sputtered CoNiCr media is reported. Cr thickness was varied from 100 to 2000 Å while the magnetic layer was maintained in the range of 260-300 Å. Measurements using a vibrating sample magnetometer show a monotonic enhancement of coercivity from 600 to 1500 Oe with increasing Cr thickness. Media noise was measured as a function of transition density using a spectrum analyzer. The media noise power at 2400 flux changes per millimeter decreased by a factor of about 10 with the increase in Cr thickness. This reduction is accompanied by a reduction in the coercivity squareness and the development of granular features in CoNiCr grains growing on the columns of the Cr underlayer. These features are consistent with a reduction of exchange coupling among CoNiCr grains