MAGNETIC ORDER OF UPT3 IN HIGH MAGNETIC-FIELDS

The weak magnetic order of the heavy-fermion superconductor UPt3 has b een investigated by elastic neutron-scattering measurements in magneti c fields up to 12 T along the a and c axes of the hexagonal crystal st ructure. The small antiferromagnetically ordered moment of 0.02 mu(B)/ (U atom) shows only a weak dependence on the applied magnetic field an d no sign of a domain repopulation for B parallel to a. In high magnet ic fields an increase in the magnetic con-elation length is observed f or magnetic fields along the c axis.