Polarised neutron study of the RCo₅intermetallic compounds. I. The cobalt magnetisation in YCo₅

Polarised and unpolarised neutron measurements have been carried out on a YCo5 single crystal. These have allowed the crystal structure to be refined and the magnetisation density distribution of this compound to be determined. The analysis of these results indicates that the moment of one of the two cobalt sites (Co1) has a very large orbital contribution as well as an important asphericity. These features are discussed in terms of the well known and unusually large magneto-crystalline anisotropy of Co in YCo5.