405 research outputs found

    Exotic magnetism on the quasi-FCC lattices of the d3d^3 double perovskites La2_2NaB′'O6_6 (B′' == Ru, Os)

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    We find evidence for long-range and short-range (ζ\zeta == 70 \AA~at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (FCC) lattices of the monoclinic double perovskites La2_2NaRuO6_6 and La2_2NaOsO6_6 respectively. Incommensurate magnetic order on the FCC lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbour and next nearest neighbour exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap Δ\Delta ∼\sim 2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally-coordinated 3d33d^3 systems, so the large gap observed for La2_2NaRuO6_6 may result from the significantly enhanced value of spin-orbit coupling in this 4d34d^3 material.Comment: 5 pages, 4 figure

    Muon spin rotation/relaxation measurements of the non-centrosymmetric superconductor Mg10Ir19B16

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    We have searched for time-reversal symmetry breaking fields in the non-centrosymmetric superconductor Mg10_{10}Ir19_{19}B16_{16} via muon spin relaxation in zero applied field, and we measured the temperature dependence of the superfluid density by muon spin rotation in transverse field to investigate the superconducting pairing symmetry in two polycrystalline samples of signficantly different purities. In the high purity sample, we detected no time-reversal symmetry breaking fields greater than 0.05 G. The superfluid density was also found to be exponentially-flat as T→\to 0, and so can be fit to a single-gap BCS model. In contrast, the lower purity sample showed an increase in the zero-field μ\muSR relaxation rate below Tc_c corresponding to a characteristic field strength of 0.6 G. While the temperature-dependence of the superfluid density was also found to be consistent with a single-gap BCS model, the magnitude as T→\to 0 was found to be much lower for a given applied field than in the case of the high purity sample. These findings suggest that the dominant pairing symmetry in high quality Mg10_{10}Ir19_{19}B16_{16} samples corresponds to the spin-singlet channel, while sample quality drastically affects the superconducting properties of this system.Comment: 6 pages, 5 figures, revised version resubmitted to PR
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