Magnetic properties of metallic fine particle systems

Abstract

A study of the magnetic properties of metallic fine particle systems in the form of magnetic fluids has been made. The fluids were prepared utilising the organometallic decomposition route (detailed separately by N. Mason, Ph.D. thesis, Durham University 1986) and single metal systems containing Fe, Co and Ni were prepared from new precursors. The properties of the first hydrocarbon based mixed metal particle systems are also reported. For systems prepared with Fe precursors it is thought that the fine particles are not in the α-Fe phase but may be amorphous and/or consist of iron carbides. Co and Ni systems result in particles with bulk-metal like structures although Co usually forms in the f.c.c. phase. The h.c.p. is also observed. The mixed metal systems were of FeCo and Ni(_3)Fe and a tendency to form the superlattice or ordered structures was observed. In both cases Fe has been lost to the particles and this is thought to be due to the formation of volatile iron compounds during preparation and/or surfactant complexes. Narrow size distributions have been obtained in all cases with mean particle diameters in the range 4-10 nm and standard deviations of between 0.8 and 1.9. The form of the size distribution has been found to be Gaussian. A study of the anisotropy of the particles using torque and magnetisation measurements has found uniaxial anisotropy with the first anisotropy constant of the order lO(^5)Jmֿ(^3).The values observed are too large to be ascribed solely to shape anisotropy. Low temperature magnetisation measurements have revealed the existence of a paramagnetic component in the fluids. Loss of magnetisation has occurred in all systems and is thought to be due to oxidation of the metal.