Interaction and size effects in magnetic nanoparticles

Magnetic nanoparticles dispersed as a ferrofluid with volumetric concentrations in the range 0.4 to 10% and sizes ranging from 59–77 Å have been studied via magnetic measurements at room and low temperatures. Remanence measurements have been used to determine switching and coupling effects. Particle size and concentration effects have been investigated and we find that the samples with higher concentrations have larger coercivities than expected due to coupling effects. Interactions have been found to be demagnetising overall as expected for dipolar interacting systems. Surface effects become evident below 10 K when thermal effects are weak.