Magnetic properties of Co-doped Nb clusters

Abstract

From magnetic deflection experiments on isolated Co doped Nb clusters we made the interesting observation of some clusters being magnetic, while others appear to be non-magnetic. There are in principle two explanations for this behavior. Either the local moment at the Co site is completely quenched or it is screened by the delocalized electrons of the cluster, i.e. the Kondo effect. In order to reveal the physical origin, we conducted a combined theoretical and experimental investigation. First, we established the ground state geometry of the clusters by comparing the experimental vibrational spectra with those obtained from a density functional theory study. Then, we performed an analyses based on the Anderson impurity model. It appears that the non-magnetic clusters are due to a complete quenching of the local Co moment and not due to the Kondo effect. In addition, the magnetic behavior of the clusters can be understood from an inspection of their electronic structure.Here magnetism is favored when the effective hybridization around the chemical potential is small, while the absence of magnetism is signalled by a large effective hybridization around the chemical potential.

Magnetic deflection of neutral sodium-doped ammonia clusters

“…The original Stern-Gerlach experiment was designed to determine the magnetic moment of isolated silver atoms; 22 later various other isolated atoms, 23 several molecules with a nonzero spin S [24][25][26][27][28][29][30][31][32][33][34] and metallic and bi-metallic clusters [35][36][37][38][39][40][41][42][43][44][45][46][47] were investigated with Stern-Gerlach setups (except for ref. 46).…”

Ab initio study of the Coulomb interaction in NbxCo clusters: Strong on-site versus weak nonlocal screening

“…This is confirmed by a comparison of the vibrational spectra obtained within DFT and experiments. 5 Furthermore, in Ref. 12 it is correctly predicted within DFT that Nb 7 Co should be non-magnetic.…”

“…[1][2][3][4] For example, in a recent work on Nb x Co clusters it is demonstrated that Nb 5 Co and Nb 7 Co are non-magnetic, while Nb 4 Co and Nb 6 Co are strongly magnetic. 5 The physical origin of this behavior can be traced back to the drastic change of the electronic structure as a function of cluster size.…”

“…12 Recently a combined theoretical and experimental investigation has been performed on Nb x Co clusters. 5 In this work the geometry is obtained from a comparison of experimentally and theoretically obtained vibrational spectra. With the geometry established the electronic structure is investigated in order to explain the magnetic properties obtained from magnetic deflection experiments.…”

“…The geometries of Nb 3 Co to Nb 7 Co and Nb 9 Co are well established from a comparison of theoretically and experimentally obtained vibrational spectra. 5 In addition NbCo and Nb 2 Co are considered, since the number of isomers is very small. All these clusters are known to be magnetic except Nb 5 Co and Nb 7 Co, which are non-magnetic.…”