Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
Roy G. Goodrich
The de Haas van Alphen (dHvA) effect is used, using the field modulation method, to study the orientation dependence of the extremal cross-sectional areas of the Fermi surface (FS) and effective masses of CexLa 1--xB6 alloys for x between 0 and 0.05. Previous measurements on these samples, using the pulsed field method, up to x = 1 showed that the FS was spin polarized at very low Ce concentration, at x = 0.05, indicating a spin polarity-dependent scattering mechanism. Moreover, the effective mass was enhanced by the increase of Ce concentration. This was the motivation for the present work which is to study in detail the topology of the FS and measure effective masses at these low Ce concentrations. The dHvA frequency corresponding to the alpha3 orbit of pure LaB 6 for the magnetic field parallel to the  axis has a value of (7.89 +/- 0.004)kT, which is in very good agreement with the original measurements on this sample. The effective mass of such an orbit is also found to be (0.66 +/- 0.03)me, which agrees with these measurements. The measurements on all samples 0 ≤ x ≤ 0.05, for this field direction, indicate that the frequencies corresponding to the alpha3 and alpha 1,2 orbits increase in a simple way with the increase of Ce concentration up to 5%. Similarly, the effective mass and the charge carrier density exhibit such behavior showing the gradual transformation of the ground state from light metal LaB6 to heavy Fermion CeB6. The angular dependence of the dHvA frequencies corresponding to the (alpha 3 and alpha1,2 orbits confirms the assumption that the FS is an ellipsoid of revolution centered at the X points of the Brillouin zone. The development of the FS from spin unpolarized LaB6 to complete polarization to the spin up state at 5% Ce in LaB6 is shown in great detail. This is in agreement with one of the existing theories. Similar measurements were performed on ferromagnetic EuB6, and the FS and effective masses were determined.
Teklu, Alem Abraha, "Magnetic Measurements of Rare Earth Hexaborides." (2000). LSU Historical Dissertations and Theses. 7232.