Magnetism at the nanoscale: The case of FePt

FexPt1-x nanoparticles prepared by organometallic synthesis and gas-phase condensation were structurally and magnetically characterised. The effective spin magnetic moments at both the Fe and Pt sites are reduced with respect to the moments in the corresponding bulk material by up to 20% and further decrease with decreasing particle size at the Fe sites. The ratio of orbital-to-effective-spin magnetic moment mu(l)/mu(eff)(S) at the S Fe sites increases from 2.1% for 6 nm particles to 3.4% for 3.4 nm particles due to the break of symmetry at the surface. A lowering of the crystal symmetry after the transformation to the chemically ordered L1(0) state yields a mu(l)/mu(eff)(S) approximate to 9% S, and is accompanied by an enhancement of the coercive field at 15 K from (36 +/- 5) mT to (292 +/- 8) mT indicating an increase of the anisotropy.