MICROSCOPIC MODEL FOR THE MAGNETIC SUBSYSTEM IN HONI2B2C

We demonstrate that the system of localized magnetic moments in HoNi2B 2C can be described by the four-positional clock model. This model, at a proper choice of the coupling constants, yields several metamagneti c phases in magnetic field at zero temperature in full agreement with the experimental phase diagram. The model incorporates couplings betwe en non-nearest neighbors in the direction perpendicular to the ferroma gnetic planes. The same model leads to a c-modulated magnetic phase ne ar the Curie temperature. The theoretical value of the modulation wave vector agrees surprisingly well with that observed by the neutron-dif fraction experiment without new adjustable parameters.