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.

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The magnetic and electronic properties of a pair Cr 6 and V 6 atomic clusters embedded in bulk Fe are determined by using a realistic spd-band Hubbard-like model. The spin density distribution is calculated self-consistently in the unrestricted Hartree-Fock approximation. The local magnetic moments mðiÞ and the density of electronic states q i ðeÞ are obtained at various atoms i of the cluster and of the surrounding Fe matrix. We consider two different orientations between the clusters, or better still the axis of symmetry of the clusters: collinear (C) and non-collinear (NC). For all the cases studied the interface magnetic coupling between cluster and matrix moments is antiparallel. The Fe moments close to the cluster are slighty reduced, and the mðiÞ of Cr and V atoms at the interface are often much larger than the Cr bulk moments (e.g. mðiÞ ¼ À1:39m B for Cr 6 in Fe in both orientations). We compare the results with the corresponding results for just one Cr 6 and V 6 atomic cluster embedded in bulk Fe.