The effect of Cr underlayer thickness on magnetic and structural properties of CoPtCr thin films

Abstract

Thin Co-based alloy films have shown important recording, magnetic, and structural changes when grown on Cr underlayers of different thicknesses. We have investigated these properties using several different CoPtCr compositions on Cr underlayers ranging from 0 to 200 nm in thickness. We report epitaxial growth of the hcp Co (11.0) planes on the (100) planes of bcc Cr for the first time on a disk appropriate for magnetic recording. The 〈11.0〉 Co preferred orientation occurs only when the Cr underlayer has a 〈100〉 preferred orientation. The 〈100〉 preferred orientation in the Cr layer results from the use of sputtering rates above 150 nm/min and only persists to thicknesses of about 50 nm. The thin Cr underlayers (<50 nm) with a 〈100〉 preferred orientation have fine well-packed grains. Thicker Cr underlayers have larger grains which are uncoupled and have a more random crystal orientation. The CoPtCr film morphologies follow these trends. The noise performance of these films improves with increasing Cr underlayer thickness and decreasing S* values. The CoPtCr films on thicker Cr (>50 nm) show no evidence of epitaxy and develop uncoupled grain structures like the Cr. The uncoupling of grains or the lack of in-plane c-axis orientation could both explain the drop in S* that has been correlated to S0/N improvement. Our results suggest that for the CoPtCr/Cr system, both grain morphology and crystallography must be considered in interpreting the changes in magnetic and recording properties.