Magnetisation of isolated single crystalline Fe-nanoparticles measured by a ballistic Hall micro-magnetometer

We present here the first magnetisation measurements on isolated single cry stalline Fe-nanoparticles performed with a ballistic Hall micro-magnetomete r. The measurements have a sensitivity of 10(4) mu(B) and thus provide us t he possibility to study the mechanisms of magnetisation reversal in a singl e nanoparticle. The magnetic properties of the nanoparticles are influenced by their crystal structure and shape, and the presence of an oxide surface layer. They exhibit curling of the magnetic moments, but also a novel hyst eresis behaviour. The spin configurations found for the system agree well w ith numerical calculations based on a Heisenberg Hamiltonian including the exchange and dipole interaction and surface anisotropy.