Anomalous magnetic enhancement by doping Mn in Co clusters

Magnetic moments of Co_NMn_M and Co_NV_M clusters (with Mn and V concentration less than 30%) are measured using Stern-Gerlach deflection method in molecular beams. Their average moments per atom as a function of impurity concentrations are studied and compared with bulk. Both Co_NMn_M and Co_NV_M clusters have higher average moments than their bulk counterpart due to reduced sizes. The average moments for Co_NMn_M clusters are found to increase with Mn concentration, opposite to that of CoMn bulk. The enhancement effect is found to be independent of cluster size and composition. Meanwhile, Co_NV_M clusters show reduction of average moments with V doping, consistent with what are expected in CoV bulk. The results are discussed within the virtual bound states model.