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arXiv · 1410.0725

The frustrated FCC antiferromagnet Ba2YOsO6: structural characterization, magnetic properties and neutron scattering studies

E. Kermarrec·C. A. Marjerrison·C. M. Thompson·D. D. Maharaj·K. Levin·S. Kroeker·G. E. Granroth·R. Flacau·Z. Yamani·J. E. Greedan·B. D. Gaulin
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Abstract

We report the crystal structure, magnetization and neutron scattering measurements on the double perovskite Ba$_2$YOsO$_6$. The $Fm\overline{3}m$ space group is found both at 290~K and 3.5~K with cell constants $a_0 = 8.3541(4)$~{\AA} and $8.3435(4)$~\AA, respectively. Os$^{5+}$ ($5d^3$) ions occupy a non-distorted, geometrically frustrated face-centered-cubic (FCC) lattice. A Curie-Weiss temperature $\theta = -772$~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 $T_{\rm N} \sim 69$~K, is revealed by magnetization, Fisher heat capacity and elastic neutron scattering, with an ordered moment of 1.65(6)~$\mu_B$ on Os$^{5+}$. The ordered moment is much reduced from either the expected spin only value of $\sim 3 \mu_B$ or the value appropriate to $4d^3$ Ru$^{5+}$ in isostructural Ba$_2$YRuO$_6$ of 2.2(1)~$\mu_B$, 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 $\Delta \sim 17$~meV, unexpected for an orbitally quenched, $d^3$ electronic configuration. We discuss this in the context of the $\sim 5$~meV spin gap observed in the related Ru$^{5+}$, $4d^3$ cubic double perovskite Ba$_2$YRuO$_6$, and attribute the $\sim 3$ times larger gap to stronger SOC present in this heavier, $5d$, osmate system.

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E. Kermarrec, C. A. Marjerrison, C. M. Thompson, D. D. Maharaj, K. Levin, S. Kroeker, G. E. Granroth, R. Flacau, Z. Yamani, J. E. Greedan, B. D. Gaulin. 2014-10-02. The frustrated FCC antiferromagnet Ba2YOsO6: structural characterization, magnetic properties and neutron scattering studies. https://doi.org/10.1103/physrevb.91.075133

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