Competing interactions and magnetic frustration in Yb₄LiGe₄

Abstract

We have studied polycrystalline Yb₄LiGe₄, a ternary variant of the R₅T₄ family of layered compounds characterized by a very strong coupling between the magnetic and crystallographic degrees of freedom. The system is mixed valent, with nonmagnetic Yb²⁺ and magnetic Yb³⁺ present, and is characterized by coexisting ferromagnetic (FM) and antiferromagnetic (AFM) correlations. We present measurements of resistivity, AC-susceptibility, specific heat, and muon spin relaxation (μSR), below 1 K. The low temperature measurements suggest a transition to a mesoscopically inhomogeneous magnetically ordered state below 2 K characterized by fluctuations well below the ordering temperature. This unusual state is believed to result from the enhanced two-dimensionality produced by Li substitution and frustration effects inherent in the Yb-sublattice geometry.