We report de Haas-van Alphen measurements in both the antiferromagetic and paramagnetic regimes of NdB6, which are shown to be separated by a second order upper critical field for antiferromagnetic ordering of H_{c} approximately 30 T when the magnetic field is parallel to [001]. The Fermi surface changes across the transition provide an ideal example of a system in which the effect of a one-dimensional magnetic periodic potential on doubling the unit cell (as originally predicted by Slater [Phys. Rev. 82, 538 (1951)]) can be tuned by varying only the magnetic field. The Fermi surface within the paramagnetic phase resembles that observed in other hexaborides such as LaB6 but with additional exchange splitting effects and weak correlations.

Quantum interference effects in the induced currents in metallic LaB6 are investigated in pulsed magnetic fields extending to 60 T and to temperatures of up to 70 K. One of the quantum interference frequencies, corresponding to an area in k space equal to the Brillouin zone, has an effective mass precisely equal to zero. The attenuation of this and other frequencies at high temperatures requires the scattering effects of phonons to be considered within the Boltzmann transport equation. © 1998 The American Physical Society.

We report susceptibility experiments in magnetic fields up to 60 T and show conclusively that the de Haas-van Alphen oscillations originate from a single spin Fermi surface. New observed frequencies present in magnetic breakdown and quantum interference oscillations indicate that the Fermi-surface topology changes as a function of the applied field while maintaining a constant volume. These results are not expected from the Anderson lattice model. © 1998 The American Physical Society.

De Haas–van Alphen measurements in CexLa1-xB6 intermetallics reveal the existence of long-lived quasiparticles for all 0

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.

We report measurements of the de Haas-van Alphen effect on a series of compounds, LaMIn5 (M=Co,Rh,Ir). The results show that each of the Co and Ir Fermi surfaces (FSs) exhibits some portions that are two dimensional and some portions that are three dimensional. The most two-dimensional character is exhibited in LaCoIn5, less two-dimensional behavior is seen in LaIrIn5, and no part of Fermi surface of LaRhIn5 is found to have a two-dimensional character. Thus the two dimensionality of portions of the FSs is largely determined by the d character of the energy bands while all of the effective masses remain ≤1.2. This fact has implications for the causes of the heavy fermion nature of superconductivity and magnetism in the Ce-based compounds having similar composition and structure. © 2009 The American Physical Society.

In this paper, we briefly review some recent de Haas-van Alphen experiments on two contrasting types of heavy fermion/Kondo systems for varying concentrations x of the impurity ion, Ce or U. In both systems the Fermi surface is observed to vary continuously with x: in CexLa1-xB6, the Ce ions behave as Kondo impurities while in UxTh1-xBe13 they do not. In both systems, the f electrons are also found to contribute only partially to the Fermi surface volume, therefore raising questions concerning the applicability of Fermi liquid theory.

The results of de-Haas-van-Alphen (dHvA) measurements on Cd doped CeCoIn5 in the high magnetic field paramagnetic phase are reported. The replacement of trivalent In by divalent Cd is known to induce an antiferromagnetic order coexisting with superconductivity in this heavy fermion superconductor. We find a small but systematic change in the dHvA frequencies with Cd doping, reflecting the chemical potential shift due to the removal of conduction electrons. The frequencies and effective masses are close to those found in the undoped compound. We observe no abrupt change in the electron Fermi surface (FS) volume in the high field paramagnetic phase for x > x c corresponding to the onset of antiferromagnetic ordering at zero magnetic field in CeCo(In1xCdx)5. Our results show that no significant change of the Fermi surface volume occurs to cause the AFM onset inside the SC state in CeCoIn5 with Cd doping. Only slight changes causing the Band 15 electron FS to be more cylindrical are observed making nesting more likely. © Published under licence by IOP Publishing Ltd.

The magnetic properties of the ground state of a low-density free-electron gas in three dimensions have been the subject of theoretical speculation and controversy for seven decades. Not only is this a difficult theoretical problem to solve, it is also a problem which has not hitherto been directly addressed experimentally. Here we report measurements on electron-doped calcium hexaboride (CaB₆) which, we argue, show that-at a density of 7× 1019 electrons cm-3-the ground state is ferromagnetically polarized with a saturation moment of 0.07 µ_B per electron. Surprisingly, the magnetic ordering temperature of this itinerant ferromagnet is 600 K, of the order of the Fermi temperature of the electron gas.