POLARIZED NEUTRON STUDY OF TBCO2

The Co and Tb contributions to the magnetic density of TbCo2 have been separated by means of diffraction experiments with polarised neutrons performed at various temperatures. The 4f Tb form factor measured at 200K is in good agreement with that calculated using the tensor operator method. As in other rare earth (R)-Co2 compounds previously studied, the Co magnetic behaviour arises from a metamagnetic transition on the 3d band with the total field acting on it. The occurrence of such a transition is correlated to a maximum in the thermal variation of the susceptibility. In the RCo2 compounds, if the 3d band susceptibility at the Curie temperature is below the maximum value, the metamagnetic transition is then observed. The transition is of first order; it is the case of HoCo2. If the susceptibility at the Curie temperature is close to the maximum value, the Co moment is induced without any discontinuity. The transition is of second order; it is the case of TbCo2.