MAGNETIC AND SPIN PROPERTIES OF TETRAHEDRAL AMORPHOUS-CARBON

Tetrahedral amorphous carbon specimens were prepared from a cathodic a re. The bond angle stiffness of sp(3) carbon requires the presence of sp(2) bonding ''defects'' to relieve network strain. The sp(2) sites, if isolated, would give rise to an electron spin. Electron spin resona nce measurements show that the spin density, although very high, is ov er an order of magnitude less than expected on the basis of a complete ly random distribution. Phosphorus doping from the vapour phase strong ly reduces the spin density. The addition of ferromagnetic impurity at oms does not affect the spin density but magnetization measurements sh ow that superparamagnetic clusters are formed. Further addition of fer romagnetic atoms is expected to produce a useful ferromagnetic materia l.