Crystal fields, disorder, and antiferromagnetic short-range order in Yb_0.24Sn_0.76Ru

We report extensive measurements on a new compound (Yb _0.24Sn_0.76)Ru that crystallizes in the cubic CsCl structure. Valence-band photoemission (PES) and L₃ x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3⁺ is split by the crystalline electric field (CEF) into a Γ₇-doublet ground state and a Γ₈ quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a Γ₆-excited state resides at 32 meV; however, the Γ₈/Γ₆ transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K there is a peak in specific heat that is too broad to represent a magnetic-phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand this peak also is too narrow to represent the Kondo effect in the Γ₇-doublet ground state. On the basis of the field dependence of the specific heat, we argue that antiferromagnetic (AF) short-range order (SRO) (possibly coexisting with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.