Fermi surfaces changes in La1-x Smx B6 and Ce1-x Cax B6 studied using the de Haas-van Alphen effect and magnetic susceptibility

We have made measurements of the de Haas-van Alphen (dHvA) effect and the magnetic susceptibility of La1-x Smx B6 for x=0, 0.05, and 0.10 and Ce1-x Cax B6 for x=0 0.01, 0.03, and 0.05 in order to see changes in the Fermi surface (FS) volume with doping using lower valence substitutions for La and Ce. The FS volume decrease in La1-x Smx B6 is found to be directly proportional to the decrease in the number of electrons contributing to the boron-based conduction band by the decrease in valence of the divalent element. Two overlapping pieces of FS in the same portion of the Brillouin zone are seen to decrease in volume to the extent that they no longer overlap. In the case of Ce1-x Cax B6 the combination of increased disorder decreasing the mean-free path due to doping and heavy effective masses results in the damping of the dHvA oscillations and no signals are observed above x=0.05. Due to the mixed valence of the Ce atoms the volume decrease is not proportional to the percent valence change. Additional magnetic-susceptibility and magnetization measurements show the changing magnetic phase diagram in Ce1-x Cax B6. In the antiferroquadrapolar state of all of the Ce1-x Cax B6 samples the near-zero applied field magnetization is seen to increase with decreasing temperature terminating in a transition to the antiferromagnetic state. © 2009 The American Physical Society