We report the first observation of a field-dependent mass in a hybridizing f-electron system. CeB6 is an ordered moment heavy fermion system with an electronic specific heat coefficient γ of order 225-300 mJ/mole K2. Using the de Haas-van Alphen effect at temperatures as low as 60 mK in steady magnetic fields as large as 22 T, we observe a cyclotron orbit of frequency 8680 T for fields along the [100] direction. The mass of this orbit was measured at eight fixed fields and found to decrease from 18me to 8me as the field increases from 12 to 22 T. The observed Fermi surface is very similar to that of LaB6, indicating that the f-electrons are largely local rather than itinerant in CeB6, a picture confirmed by bandstructure calculations. The observed field dependence of the cyclotron mass is consistent with the low-energy scale of the system as measured, for example, by the Kondo temperature. Our results are compared with Fermi surface observations in other heavy fermion systems.

The effective mass of the itinerant electrons in the Kondo lattice system CeB6 is found to be strongly field dependent. Measurements of the de Haas-van Alphen effect at temperatures down to 60 mK in steady magnetic fields up to 22 T show a change of more than 100% in the cyclotron effective mass, decreasing with increasing field. The origin of the effect is not known but it is noted that a field of about 10 T corresponds to the energy scales in the system. © 1987 The Japan Society of Applied Physics.

Low-temperature, high-field deHaas van Alphen measurements are presented which show that the conduction-electron mass in the Kondo lattice CeB6 decreases strongly with field. This field dependence is consistent with recent specific-heat results. The geometry of the Fermi surface does not depend on field. Thus we observe a reduction in the many-body enhancement of the electronic density of states at the Fermi energy which is described by a change of the itinerant-electron mass alone; the number of particles and the occupation of states in k space remain unchanged. We argue that CeB6 represents a different limit of heavy-fermion behavior as compared to UPt3. © 1987 The American Physical Society.

We have used neutron scattering techniques to examine the magnetic transitions in the Ho1-xErxRh4B4 pseudoternary system. A wide variety of behavior is found, ranging from mean-field behavior for HoRh4B4 to complicated behavior for ErRh4B4, where superconductivity and long-range ferromagnetic order coexist between 0.7 and 1.2 K. Long-range ferromagnetic order is found at the lowest temperatures for all alloy compositions. Alloys with more than about 30% Ho order magnetically along the c axis and superconductivity is destroyed in these alloys in a sharp transition coincident with magnetic ordering. Alloys near the ErRh4B4 composition order in the basal plane but undergo a complex ordering process through a sinusoidally modulated state. Because Ho and Er have competing orthogonal magnetic anisotropies, compounds near the composition Ho 0.25Er0.75Rh4B4 are near a multicritical point in the magnetic phase diagram.

Superconductivity and magnetism are two types of order that can take place in materials at low temperatures. When the magnetic order is ferromagnetic, a competition exists between magnetism and superconductivity. Neutron scattering has been used to measure the interaction of magnetism and superconductivity in a series of ternary rare-earth alloys. A wide range of behavior is found near the magnetic transition, including mean-field magnetic ordering, first-order transitions between magnetism and superconductivity, and co-existence of ferromagnetism and superconductivity with a sinusoidally-modulated magnetic phase. © 1983.