Different contributions of the two cobalt sites to the magnetocrystalline anisotropy of YCo5and related compounds

The properties of permanent magnets based on RCo
5
compounds arise from their strong uniaxial anisotropy. The anisotropy field at 4.2 K in YCo
5
is about 200 kOe. A polarized neutron study of YCo
5
revealed a very large orbital contribution to the magnetic moment on the Co
I
(2c) site, which indicates that the major part of the cobalt anisotropy originates from this site. The variations of the magnetic anisotropy of YCo
5
which occur when different substitutional atoms (Ni, Fe, Co pairs) modify the ideal structure, are in agreement with this view.