Ferromagnetic Properties of Ultra Fine Metal Particles

Ferromagnetic ultra metallic fine particles of Fe, Ni and Co were prepared by a gas evaporation method in the pressure of nitrogen gas from 0.5-4Torr. Fine structures of these particles were revealed by a transmission electron microscope and a scanning electron microscope (SEM). Magnetic properties of the particles were measured by a vibrating sample magnetometer. The Fe, Ni and Co ultra fine particles observed by SEM were regarded as spheres and their surfaces were composed of oxide layers Fe sub 3 O sub 4 , NiO and CoO, respectively. The maximum coercivity was 1320, 1160 and 2900 Oe, respectively, for Co (425 A), Fe (310 A) and Ni (415 A) at room temperature. The exchange magnetic anisotropy between the cobalt core and the cobalt oxide shell was observed when the Co ultra fine particles were cooled in an applied field of 7 kOe from room temperature to 77K.