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. Magnetiza tion and Mossbauer spectroscopy investigations were combined in order to study superparamagnetic relaxation phenomena. The particles were pr epared by thermal decomposition of Fe(CO)5. This preparation method is known to produce almost mono-size particles. The mean particle diamet er of the Fe-C particles in the present study was about 3.1 nm. The sm all size resulted in finite size effects, which, e.g. for the temperat ure dependence of the saturation magnetization gave a significant devi ation from the T3/2 law. The deviation is in accord with recent theore tical calculations of the behaviour of spin waves in ultrafine particl es. From the superparamagnetic relaxation studies the minimum relaxati on time was estimated to be about 2 x 10(-12) s.