The further development of computer hard disk technology involves ever increasing density of information storage. Current levels of recording are about 1 Gbit per square inch, which will increase by a factor often over the next couple of years. The methodology is well-established: ferromagnetic cobalt alloy thin films (≈20 nm) are sputtered onto an appropriate substrate. Improvement in the magnetic performance (e.g., coercivity, signal-to-noise) requires manipulation of the microstructure by the deposition conditions. Transmission electron microscopy (TEM) is really the only characterization tool which can yield all the necessary information (structural, chemical and magnetic) because of the dimensions involved (e.g., grain sizes of 10-20 nm, with grain boundary segregation an important consideration). This article illustrates some recent contributions to understanding the structure-property-processing combination in this rapidly developing area.

The typical hard disk is made up from an aluminum alloy substrate, a 5-10 micron thick, hard NiP electrodeposited layer, a chromium underlayer, the magnetic Co alloy and a protective thin carbon overcoat.