Unravelling competing microscopic interactions at a phase boundary: a single crystal study of the metastable antiferromagnetic pyrochlore Yb$_{2}$Ge$_{2}$O$_{7}$

TL;DR

This study uses neutron scattering and EPR to precisely determine exchange interactions in Yb2Ge2O7, revealing its proximity to a classical magnetic phase boundary and highlighting Yb pyrochlores as key systems for quantum magnetism research.

Contribution

The paper provides the first direct measurement of the anisotropic exchange parameters and g-tensor in Yb2Ge2O7, clarifying its position near a classical phase boundary and demonstrating the importance of combined techniques.

Findings

Yb2Ge2O7 is close to a classical phase boundary between magnetic phases.

The exchange parameters are strongly correlated with the g-tensor components.

Yb pyrochlores are ideal for studying quantum magnets near phase boundaries.

Abstract

We report inelastic neutron scattering measurements from our newly synthesized single crystals of the structurally metastable antiferromagnetic pyrochlore Yb$_{2}$Ge$_{2}$O$_{7}$. We determine the four symmetry-allowed nearest-neighbor anisotropic exchange parameters via fits to linear spin wave theory supplemented by fits of the high-temperature specific heat. The exchange parameters so-determined are strongly correlated to the values determined for the $g$-tensor components, as previously observed for the related Yb pyrochlore Yb$_{2}$Ti$_{2}$O$_{7}$. To address this issue, we directly determined the $g$-tensor from electron paramagnetic resonance of 1% Yb-doped Lu$_{2}$Ge$_{2}$O$_{7}$, thus enabling an unambiguous determination of the exchange parameters. Our results show that Yb$_{2}$Ge$_{2}$O$_{7}$ resides extremely close to the classical phase boundary between an antiferromagnetic $\Gamma_5$ phase and a splayed ferromagnet phase. By juxtaposing our results with recent ones on Yb$_{2}$Ti$_{2}$O$_{7}$, our work illustrates that the Yb pyrochlore oxides represent ideal systems for studying quantum magnets in close proximity to classical phase boundaries.