Spin gap and the nature of the 4d3magnetic ground state in the frustrated fcc antiferromagnet Ba2YRuO6

Abstract

The geometrically frustrated double perovskite Ba2YRuO6 has magnetic 4d 3 Ru 5+ ions decorating an undistorted face-centered cubic (FCC) lattice. This material has been previously reported to exhibit commensurate long-range antiferromagnetic order below TN ∼ 36 K, a factor f ∼ 15 times lower than its Curie-Weiss temperature ΘCW = −522 K, and purported short-range order to T * = 47 K. We report new time-of-flight neutron spectroscopy of Ba2YRuO6 which shows the development of a ∼5 meV spin gap in the vicinity of the [100] magnetic ordering wavevector below TN =36 K, with the transition to long-range order occurring at T * = 47 K. We also report spin waves extending to ∼14 meV, a surprisingly small bandwidth in light of the large ΘCW . We compare the spin gap and bandwidth to relevant neutron studies of the isostructural 4d 1 material Ba2YMoO6, and discuss the results in the framework of relatively strong spin-orbit coupling expected in 4d magnetic systems.

Diffuse magnetic neutron scattering in the highly frustrated double perovskiteBa2YRuO6

“…Analysis by x-ray powder diffraction showed a single phase product with a unit cell constant identical within statistical error with that reported. This sample is from the same batch as used in the inelastic neutron scattering experiments described previously 15 . A polarized neutron scattering experiment was carried out on the diffuse scattering spectrometer D7 at the ILL.…”

“…However, later neutron scattering studies including energy analysis, demonstrated that the (100) and (110) magnetic reflections remained resolution limited up to 47 K with a low incident energy and a narrow energy analysis window 15 . Upon widening the energy analysis window, the data more closely resembled those of the original diffraction experiments.…”

“…In the case of Sr 2 YRuO 6 , the peak shape is interpreted as Warren-like 16 , while for Ba 2 YRuO 6 the dimensionality of correlations is less obvious to assign; indeed, it is possible to fit the peak using either an asymmetric 2D Warren or a symmetric 3D Lorentzian lineshape function. Matters are complicated by the presence of quasi-elastic critical scattering around Q 100 at high temperature, which has already been shown to have a highly asymmetric lineshape 15 . The T > 40 K data from D7 clearly contains a significant contribution from this inelastic scattering, given the absence of energy analysis.…”

“…6. S(Q, E) measured at 75 K from [15]. The detector trajectories integrated over in our polarized scattering experiments are indicated by white lines.…”

Time-of-Flight Elastic and Inelastic Neutron Scattering Studies on the Localized 4d Electron Layered Perovskite La5Mo4O16

“…In fact, similar spin gaps in the long-range magnetic ordered state were observed in 3d 30) and other 4d electron systems. [31][32][33] …”