SEARCH FOR A SPONTANEOUS MAGNETIZATION IN THE SUPERCONDUCTING B-PHASEOF UPT3

We report the results of a search for a spontaneous magnetization in t he superconducting B-phase of UPt3 which is predicted to exist because of broken time-reversal symmetry. We have measured the change of magn etic flux upon the superconducting transition in a field very close to zero by using a SQUID magnetometer. Our result gives the upper limit of 2 mG for the spontaneous internal held, one order of magnitude smal ler than obtained by a recent mu SR measurement. The small value favor s the theory of orbital degeneracy of the pair wave function over the theory of spin degeneracy.