Insights into structural, magnetic, and crystal electric field effects of Yb ³⁺ (J eff = 1/2) in double perovskites Ba ₂ Yb B O ₆ ( B = Sb, Nb) with edge-sharing tetrahedral geometry

Geometrically frustrated magnets based on edge-sharing tetrahedral networks provide a platform for unconventional magnetic ground states. We investigate the structural, magnetic, thermodynamic, and crystal electric field (CEF) properties of the double perovskites Ba 2 Yb B O 6 ( B = Sb, Nb), where Yb 3+ ions form a three-dimensional face-centered cubic lattice of edge-sharing tetrahedra. Magnetic susceptibility reveals antiferromagnetic interactions with Curie-Weiss temperatures θ CW = -104.21 K and -101.64 K for Ba 2 YbSbO 6 and Ba 2 YbNbO 6 in the high temperature region and -0.08 K and -0.15 K in the low temperature region, respectively, and no long-range magnetic order down to 2 K. Specific heat and magnetization measurements support the absence of magnetic ordering. Debye-Einstein analysis yields Debye temperatures θ D = 345 K and 310 K for the Sb and Nb compounds, respectively. CEF modelling based on a point-charge approach establishes a Kramer's doublet ground state with an effective J eff = ½ for Yb 3+ , governing the low-temperature behaviour.