Antiferromagnetism and Its Relation to the Superconducting Phases of UPt3

Using magnetic x-ray and neutron diffraction in UPt3, we find that a suppression of the antiferromagnetic scattering intensity in the superconducting phase is due to a reduction in the magnitude of the staggered moment with no change in symmetry. The existence of the suppression as well as the magnetic correlation lengths are not affected by the presence or absence of a visible splitting in the superconducting transition. The simplest models wherein antiferromagnetic order provides the symmetry-breaking field for the splitting do not provide a compete explanation of our results

Divergent effects of static disorder and hole doping in geometrically frustrated b-CaCr2O4

The gallium substituted and calcium deficient variants of geometrically frustrated b-CaCr2O4, b-CaCr2-2xGa2xO4 (0.02<= x<= 0.25) and b-Ca1-yCr2O4 (0.075<= y<= 0.15), have been investigated by x-ray powder diffraction, magnetization and specific heat measurements. This allows for a direct comparison of the effects, in a geometrically frustrated magnet, of the static disorder that arises from non-magnetic substitution and the dynamic disorder that arises from hole doping. In both cases, disturbing the Cr3+ lattice results in a reduction in the degree of magnetic frustration. On substitution of Ga, which introduces disorder without creating holes, a gradual release of spins from ordered antiferromagnetic states is observed. In contrast, in the calcium deficient compounds the introduction of holes induces static ferrimagnetic ordering and much stronger perturbations of the b-CaCr2O4 host.Comment: 23 pages, 10 figure