5. Magnetic nanomaterials

5.1 Magnetic hard disk drive material

The active part of a hard disk consists of a layer of nanocrystalline magnetic material (grain size: approx. 10 nm). In the ferromagnetic state, and for very small crystals, each crystal carries a magnetic moment (see § 1.3). In order to take account of the scattered characteristics of crystalline grains, it is appropriate to include around a hundred of them in one unit of information (bit).

One of the challenges of disc technology is to preserve magnetic information over very long periods (> 10 years). This presupposes...