Polarised neutron study of HoCo₂

Diffraction experiments with polarised neutrons have been carried out on a HoCo 2 single crystal at various temperatures and in several applied fields up to 57 kOe. The Ho and Co contributions have been analysed. The 4f Ho form factors measured in the ordered and paramagnetic states are in good agreement with those calculated using the tensor-operator method. At low temperature, a discrepancy is observed at small scattering angles, indicating the presence of a diffuse density. The magnetic scattering amplitudes, measured for reflections to which the 4f Ho moment does not contribute, are characteristic of a 3d type Co form factor on both sides of the ordering temperature. The paramagnetic Co susceptibility is of Pauli type. Below the ordering temperature, the large molecular field involves a sudden increase of the Co susceptibility.