Frustrated fcc antiferromagnet Ba 2 YOsO 6 : Structural characterization, magnetic properties, and neutron scattering studies
Résumé
We report the crystal structure, magnetization and neutron scattering measurements on the double perovskite Ba2YOsO6. The F m3m space group is found both at 290 K and 3.5 K with cell constants a0 = 8.3541(4) Å and 8.3435(4) Å, respectively. Os 5+ (5d 3) ions occupy a non-distorted, geometrically frustrated face-centered-cubic (FCC) lattice. A Curie-Weiss temperature θ ∼ −700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long range antiferromagnetic order, consistent with a Type I FCC state below TN ∼ 69 K, is revealed by magnetization, Fisher heat capacity and elastic neutron scattering, with an ordered moment of 1.65(6) µB on Os 5+. The ordered moment is much reduced from either the expected spin only value of ∼ 3µB or the value appropriate to 4d 3 Ru 5+ in isostructural Ba2YRuO6 of 2.2(1) µB, suggesting a role for spin orbit coupling (SOC). Triple axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T = 67.45 K, and the existence of a second ordered state. Time-of-flight inelastic neutron results reveal a large spin gap ∆ ∼ 17 meV, unexpected for an orbitally quenched, d 3 electronic configuration. We discuss this in the context of the ∼ 5 meV spin gap observed in the related Ru 5+ , 4d 3 cubic double perovskite Ba2YRuO6, and attribute the ∼ 3 times larger gap to stronger SOC present in this heavier, 5d, osmate system.
Domaines
| Origine | Fichiers produits par l'(les) auteur(s) |
|---|---|
| Licence |