Unravelling competing microscopic interactions at a phase boundary: A single-crystal study of the metastable antiferromagnetic pyrochlore <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Yb</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Ge</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math>
Colin L. Sarkis, Jeffrey G. Rau, Liurukara D. Sanjeewa, Matthew Powell, Joseph W. Kolis, Jonathan Marbey, Stephen Hill, J. A. Rodriguez‐Rivera, Harikrishnan S. Nair, D. R. Yahne, S. Säubert, Michel J. P. Gingras, K. A. Ross
Abstract
We report inelastic neutron scattering measurements from our newly synthesized single crystals of the structurally metastable antiferromagnetic pyrochlore ${\mathrm{Yb}}_{2}{\mathrm{Ge}}_{2}{\mathrm{O}}_{7}$. 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 using the numerical linked-cluster expansion method. The exchange parameters so determined are strongly correlated to the values determined for the $g$-tensor components, as previously noted for the related Yb pyrochlore ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$. To address this issue we directly determined the $g$ tensor from electron paramagnetic resonance of 1% Yb-doped ${\mathrm{Lu}}_{2}{\mathrm{Ge}}_{2}{\mathrm{O}}_{7}$, thus enabling an unambiguous determination of the exchange parameters. Our results show that ${\mathrm{Yb}}_{2}{\mathrm{Ge}}_{2}{\mathrm{O}}_{7}$ resides extremely close to the classical phase boundary between an antiferromagnetic ${\mathrm{\ensuremath{\Gamma}}}_{5}$ phase and a splayed ferromagnet phase. By juxtaposing our results with recent ones on ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$, our work illustrates that the Yb pyrochlore oxides represent ideal systems for studying quantum magnets in close proximity to classical phase boundaries.