Scaling between magnetization and Drude weight in EuB6

The low-temperature optical response of EuB6 is strongly influenced by a ferromagnetic phase transition with a zero-field onset temperature TC of ;16 K. A marked blueshift of the reflectivity plasma edge with either decreasing temperature or increasing magnetic field is observed. The corresponding temperature and fielddependent plasma-frequency shift, combined with low-field Hall data, reveals a distinct reduction of the effective mass of the itinerant charge carriers, in parallel with the onset of ferromagnetic order. A universal scaling linking the experimental data on magnetization and the Drude weight is established.