Surface contribution to the anisotropy energy of spherical magnetite particles

The surface contribution to the magneto-crystalline anisotropy energy of spherical magnetite nanoparticles has been investigated. Magnetite particles of three sizes (3.5, 7, and 18nm diameter) were grown inside protein cages. Alternating current magnetic susceptibility measurements revealed the particles to be noninteracting, and allowed a determination of the average anisotropy energy for each sample. Surface atoms were found to increase the volume anisotropy energy density of the particles, and this effect increased sublinearly with particle curvature.