MAGNETIZATION AND MOSSBAUER STUDIES OF ULTRAFINE FE-C PARTICLES

The magnetic properties of ultrafine amorphous Fe1-xCx particles have been studied as a function of temperature and applied field. Magnetization and Mossbauer spectroscopy investigations were combined in order to study superparamagnetic relaxation phenomena. The particles were prepared by thermal decomposition of Fe(CO)5. This preparation method is known to produce almost mono-size particles. The mean particle diameter of the Fe-C particles in the present study was about 3.1 nm. The small size resulted in finite size effects, which, e.g. for the temperature dependence of the saturation magnetization gave a significant deviation from the T3/2 law. The deviation is in accord with recent theoretical calculations of the behaviour of spin waves in ultrafine particles. From the superparamagnetic relaxation studies the minimum relaxation time was estimated to be about 2 x 10(-12) s.