Antiferromagnetic-like coupling in the cationic iron cluster of thirteen atoms.

We explore, within the density functional theory in the generalized gradient approximation to exchange and correlation, the map of spin isomers of the cationic Fe13(+) cluster in connection with recent X-ray magnetic circular dichroism spectroscopy experiments [M. Niemeyer et al., Phys. Rev. Lett. 2012, 108, 057201] which showed an anomalous low magnetic moment per number of 3d holes in this cluster. We systematically explore the low-lying magnetic excitations and correlate them with structural rearrangements and stability indicators. We obtain the observed low magnetic moment per 3d hole as the ground state of Fe13(+) and we demonstrate that, as supposed by the experimentalists, the cluster undergoes a magnetic transition from a ferromagnetic-like configuration to an antiferromagnetic-like one upon ionization. We unravel this unexpected magnetic behavior showing that it is concomitant with a Th-deformation of the icosahedral structure together with the electronic filling of this particular iron cluster. The spin-orbit interaction preserves this magnetic configuration which is essentially due to the spin. Our computed magnetic anisotropy energy supports the experimental interpretation of the cluster as fluxional due to the very weak coupling of the magnetic moment to an easy axis.

Magnetic properties of a pair of V4 interacting clusters in a Fe matrix.

The magnetic properties of a pair V4 atomic clusters embedded in bulk Fe are determined by using a realistic spd-band Hubbard-like model. The spin density distribution is calculated self-consistenly in the unrestricted Hartree-Fock approximation. The local magnetic moments mu(i) are obtained at various atoms i of the cluster and of the surrounding Fe matrix. We consider two different geometrical arrangements for V clusters, collinear (C) and non-collinear (NC). In all the cases studied the magnetic coupling in the interface cluster-matrix is antiferromagnetic, and the ferromagnetic order of the matrix is not broken by the presence of the V atoms, although the local magnetic moments of Fe atoms at the interface cluster-matrix, are reduced respect to Fe bulk magnetization (2.22 microB) about 8%-20%. We compare the results with those of just one V4 atomic cluster embedded in bulk Fe.