Soft Ferromagnetic Materials Based on Iron/Carbon Multilayer

Magnetically soft ferromagnetic materials are sought after for applications in high density magnetic recording. The recording head of a magnetic memory device requires a magnetically soft material with good wear properties to imprint the signal in the magnetic recording medium. The trend to increasing recording densities has led to designs in which the magnetization is perpendicular to the surface and this requires a magnetically soft underlayer to assist in the creation of the perpendicular field. Tetrahedral amorphous carbon (ta-C) is a form of amorphous carbon in which there is a high density of unpaired spins which can lead to paramagnetism and under some conditions, superparamagnetism. We have prepared multilayers consisting of alternating layers of iron and ta-C using pulsed cathodic arc deposition. The magnetic hysteresis curves of the resulting multilayers were measured in a SQUID magnetometer and the magnetic properties were studied a function of the thickness of the layers. For some combinations, the materials become very soft and have a higher permeability than pure iron. We propose a model for the behaviour of the multilayers in which magentisation arising from the carbon paramagnetic spins couples to the iron magnetic domains.