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arXiv · 1404.6438

Incipient Ferromagnetism in Tb2Ge2O7: Application of Chemical Pressure to the Enigmatic Spin Liquid, Tb2Ti2O7

A. M. Hallas·J. G. Cheng·A. M. Arevalo-Lopez·H. J. Silverstein·Y. Su·P. M. Sarte·H. D. Zhou·E. S. Choi·J. P. Attfield·G. M. Luke·C. R. Wiebe
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Abstract

The origin of the spin liquid state in Tb$_2$Ti$_2$O$_7$ has challenged experimentalists and theorists alike for nearly 20 years. To improve our understanding of the exotic magnetism in Tb$_2$Ti$_2$O$_7$, we have synthesized a chemical pressure analog, Tb$_2$Ge$_2$O$_7$. Germanium substitution results in a lattice contraction and enhanced exchange interactions. We have characterized the magnetic ground state of Tb$_2$Ge$_2$O$_7$ with specific heat, ac and dc magnetic susceptibility, and polarized neutron scattering measurements. Akin to Tb$_2$Ti$_2$O$_7$, there is no long-range order in Tb$_2$Ge$_2$O$_7$ down to 20 mK. The Weiss temperature of $-$19.2(1) K, which is more negative than that of Tb$_2$Ti$_2$O$_7$, supports the picture of stronger antiferromagnetic exchange. Polarized neutron scattering of Tb$_2$Ge$_2$O$_7$ reveals that at 3.5 K liquid-like correlations dominate in this system. However, below 1 K, the liquid-like correlations give way to intense short-range ferromagnetic correlations with a length scale related to the Tb-Tb nearest neighbor distance. Despite stronger antiferromagnetic exchange, the ground state of Tb$_2$Ge$_2$O$_7$ has ferromagnetic character, in stark contrast to the pressure-induced antiferromagnetic order observed in Tb$_2$Ti$_2$O$_7$.

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A. M. Hallas, J. G. Cheng, A. M. Arevalo-Lopez, H. J. Silverstein, Y. Su, P. M. Sarte, H. D. Zhou, E. S. Choi, J. P. Attfield, G. M. Luke, C. R. Wiebe. 2014-12-03. Incipient Ferromagnetism in Tb2Ge2O7: Application of Chemical Pressure to the Enigmatic Spin Liquid, Tb2Ti2O7. https://doi.org/10.1103/physrevlett.113.267205

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