Last year a short item was published in this journal to draw attention to two papers from scientists at the Philips Research Laboratories, in the Netherlands, and at the E. I. du Pont de Nemours Experimental Station, U.S.A., both of which reported investigations into the magnetic and magneto-optic properties of cobalt/platinum layered structures (1). In the same issue an abstract of a communication from the Sony Corporation Research Center, Yokohama, Japan, on the properties of ultrathin multilayer films was published (2). Now two further papers from these Japanese researchers have appeared (3, 4).

Amorphous rare-earth transition-metal films used as magneto-optical recording media are easily oxidised and an additional element is required to provide resistance to corrosion. For these reasons, and because the magneto-optical properties of currently used media decrease at the shorter wavelengths favoured for higher density recording, investigations to find superior materials are continuing. The recent paper describes the magneto-optical and magnetic properties of ultrathin cobalt/platinum and cobalt/palladium multilayers.

The structure of these multilayered films, their magneto-optical and magnetic properties and the dependence of these on film thickness are reported and discussed, as is the dependence of the magneto-optical properties on light wavelength. Corrosion resistance of these multilayers is high and they are thermally stable at temperatures of up to 400°C.

It is reported that at 780 nm the magneto-optical properties of ultrathin cobalt/platinum films are superior to those of TbFeCo films, while at shorter wavelengths the figure of merit is even better, being 2.5 times larger than that of TbFeCo at 400 nm.

A further communication by the same authors, on the potentially useful magnetic properties of rf magnetron sputtered thin films of cobalt-palladium alloys, is abstracted on page 99 of this journal.