THE INFLUENCE OF PARTICLE-SIZE AND INTERACTIONS ON THE MAGNETIZATION AND SUSCEPTIBILITY OF NANOMETER-SIZE PARTICLES

We studied the magnetic properties of frozen magnetic liquids containi ng amorphous Fe1-xCx particles. By varying the particle size and conce ntration, we could separate single-particle effects from interactions. In samples containing particles with median diameters 5.0 nm and 3.8 nm and with spontaneous saturation magnetizations 7.1 kA m(-1) and 9.2 kA m(-1), effects of particle interactions are observed. For 3.2 nm n o interactions were observed. In samples with negligible interactions the superparamagnetic blocking temperature increases with the particle size. The effective anisotropy constant increases with decreasing par ticle size, implying that the anisotropy is enhanced by surface effect s.