Magnetism of small V clusters embedded in a Cu fcc matrix: an ab initio study

We present extensive first principles density functional theory (DFT) calculations dedicated to analyze the magnetic and electronic properties of small V (n) clusters (n = 1, 2, 3, 4, 5, 6) embedded in a Cu fcc matrix. We consider different cluster structures such as: (i) a single V impurity, (ii) several V-2 dimers having different interatomic distance and varying local atomic environment, (iii) V-3 and (iv) V-4 clusters for which we assume compact as well as 2- and 1-dimensional atomic configurations and finally, in the case of the (v) V-5 and (vi) V-6 structures we consider a square pyramid and a square bipyramid together with linear arrays, respectively. In all cases, the V atoms are embedded as substitutional impurities in the Cu network. In general, and as in the free standing case, we have found that the V clusters tend to form compact atomic arrays within the cooper matrix. Our calculated non spin-polarized density of states at the V sites shows a complex peaked structure around the Fermi level that strongly changes as a function of both the interatomic distance and local atomic environment, a result that anticipates a non trivial magnetic behavior. In fact, our DFT calculations reveal, in each one of our clusters systems, the existence of different magnetic solutions (ferromagnetic, ferrimagnetic, and antiferromagnetic) with very small energy differences among them, a result that could lead to the existence of complex finite-temperature magnetic properties. Finally, we compare our results with recent experimental measurements.