Dependence of magnetics, microstructures and recording properties on underlayer thickness in conicr/cr media

Abstract

This work reports the effect of Cr underlayer thickness on the magnetic, microstructural and recording properties of sputtered CoNiCr media. Cr thickness was varied from 100 to 2000 A while the magnetic layer was maintained in the thickness range of 260-300 A. 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 was found to decrease by a factor of about 10 with the increase in Cr thickness. This reduction in noise is accompanied by a reduction in the coercivity squareness, S*, and a development of granular features in CpNiCr grains growing on the columns of Cr underlayer as seen in TEM micrographs. These features are consistent with a reduction of exchange coupling among CoNiCr grains based on a previous theoretical study as well as with a similar effect reported previously for Co-alloy media. © 1988 IEEE