Role of the chemical ordering on the magnetic properties of Fe–Ni cluster alloys
CEA/DSM/DRECAM/SPCSI, CE de Saclay, 91191 Gif-sur-Yvette, France
2 Instituto de Física “Manuel Sandoval Vallarta", Universidad Autónoma de San Luis Potosí, Alvaro Obregón 64, 78000 San Luis Potosí, México
3 Laboratoire de Physique des Solides, Bâtiment 510, Université Paris-Sud, Centre d'Orsay, 91405 Orsay, France
Published online: 12 July 2005
The spin and orbital moments of fcc Fe-Ni cluster alloys are determined within the framework of a d-band Hamiltonian including the spin-orbit coupling non perturbatively. Different sizes (up to 321 atoms), compositions, and chemical configurations (random alloys as well as core-shell arrays of iron and nickel atoms) are considered in order to reveal the crucial role played by local order and stoichiometry on the magnetic moments of the clusters. Interestingly, we have found considerably reduced average magnetizations for Fe-Ni clusters with Fe cores compared to that of the bulk alloy with the same composition. Indeed, in these configurations not only antiparallel arrangements between the local moments of some Fe atoms within the iron core are found, but also the total magnetization of the surface Ni atoms is significantly quenched. On the opposite, the disordered and Ni-core cluster alloys are characterized by high magnetizations resulting from saturated-like contributions from both Ni and Fe atoms, in agreement with recent ab-initio calculations. In general, the local orbital magnetic moments are strongly enhanced with respect to their bulk values. Finally, the variation of the orbital-to-spin moment ratio with the chemical order is discussed.
PACS: 73.22.-f – Electronic structure of nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals / 61.46.+w – Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals / 75.75.+a – Magnetic properties of nanostructures
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2005