Magnetic properties of Ni-Rh clusters: Behavior in the Ni-rich region

We study the magnetic properties of bimetallic Ni-Rh 55-atom clusters in the Ni-rich region as a function of Rh composition. The minimum energy structures are taken from Molecular Dynamics Simulations by using empirical potentials (in the Second Moment Approximation). We then calculate the electronic and magnetic properties of these structures by using a tight-binding Hamiltonian. The magnetic solutions are found solving a Hubbard-like Hamiltonian within the unrestricted Hartree-Fock Approximation. Bulk parameters and Andersen's exponential law for the dependence of hopping on distance are being used. We obtain that a small number of Rh atoms can modify the average magnetic moment, μ, depending not only on the positions of the Rh atoms (either on the surface-, middle-, or central-shell) but also on their relative positions. The magnetic moment curve corresponding to the minimum energy structures shows a minimum for 2 Rh atoms and there is an enhancement of μ up to 6 Rh atoms, being the μ value of this last cluster even higher than the one corresponding to Ni55 clusters