Anomalous behavior of the dHvA oscillations in CexLa1−xRu2Si2

We report anomalous behaviors of the de Haas – van Alphen (dHvA) oscillations in various CexLa1−xRu2Si2 samples when magnetic field is applied in the (001) plane. We argue that these behaviors can be explained by assuming that the effective mass of the conduction electron of one spin direction decreases with field while that of the opposite spin direction increases.