de Haas-van Alphen study of the Fermi Surface of Ce$_{x}$La$_{1-x}$B$_{6}$ as a function of composition: the evolution of field-dependent quasiparticle effective masses

The de Haas-van Alphen effect has been studied in single crystals of Ce$_{x}$La$_{1-x}$B$_{6 }$ (0 $\le \quad x \quad \le $ 0.075) using pulsed magnetic fields of up to 60 T and temperatures 0.38 K $\le \quad T \quad \le $ 4.0~K. The low-field effective mass grows smoothly with increasing $x. $Moreover, for $x \quad >$ 0, the effective mass becomes a function of magnetic field, decreasing as the field rises. These results may be fitted using the extended Lifshitz-Kosevich formalism due to Wasserman, the decrease in mass reflecting the suppression of spin fluctuations by the field. The data also show that a previously-observed effect, attributed to complete spin polarization of one of the Fermi-surface sheets for $x \ge $ 0.05, is in fact an artifact of the field-dependent mass, ignored in previous works.