FERMI-SURFACE PROPERTIES OF FERROMAGNETIC CERU2GE2

We have performed a dHvA effect study on the ferromagnetic heavy fermi on compound CeRu2Ge2. Six spin-split dHvA frequency branches are obser ved in the (100) and (110) planes. The angular dependence of the dHvA frequencies is mostly consistent with the result reported by King and Lonzarich (KL), except that we have successfully observed the dHvA sig nal from a large hole surface for fields parallel to [001] and a new l ow-frequency branch. The effective masses measured for fields in the ( 001) plane agree with those of KL and do not depend on field strength. On the other hand, those for fields parallel to [001] differ consider ably from those of KL and are found to decrease with increasing field. Moreover, the measured effective mass of the large hole surface is le ss than half of the value expected from the electronic specific heat c oefficient.