We performed measurements of the Hall effect, electrical resistivity, and magnetization on random alloys of Nd1-xCaxB6 (x < 0.4) in the 2 to 300 K temperature range, and in magnetic fields of up to 5 T. We find that a large anomalous contribution to the Hall effect, observed in NdB6 single crystals in the paramagnetic regime, decreases sharply with Ca content. In addition, the electron concentration decreases as expected for a divalent substitution for trivalent Nd. We tentatively relate these observations to changes in the Fermi surface volume upon doping. © 2010 IOP Publishing Ltd.

Many superconducting materials allow the penetration of magnetic fields in a mixed state in which the superfluid is threaded by a regular lattice of Abrikosov vortices, each carrying one quantum of magnetic flux. The phenomenological Ginzburg-Landau theory, based on the concept of characteristic length scales, has generally provided a good description of the Abrikosov vortex lattice state. We conducted neutron-scattering measurements of the vortex lattice form factor in the heavy-fermion superconductor cerium-cobalt-indium (CeCoIn5) and found that this form factor increases with increasing field-opposite to the expectations within the Abrikosov-Ginzburg-Landau paradigm. We propose that the anomalous field dependence of the form factor arises from Pauli paramagnetic effects around the vortex cores and from the proximity of the superconducting state to a quantum critical point.