Incipient ferromagnetism in Tb2Ge2O7: application of chemical pressure to the enigmatic spin-liquid compound Tb2Ti2O7.

摘要: After nearly 20 years of study, the origin spin-liquid state in ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ remains a challenge for experimentalists and theorists alike. To improve our understanding exotic magnetism ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$, we synthesize chemical pressure analog: ${\mathrm{Tb}}_{2}{\mathrm{Ge}}_{2}{\mathrm{O}}_{7}$. Substitution titanium by germanium results lattice contraction enhanced exchange interactions. We characterize magnetic ground ${\mathrm{Tb}}_{2}{\mathrm{Ge}}_{2}{\mathrm{O}}_{7}$ with specific heat, ac dc susceptibility, polarized neutron scattering measurements. Akin to there is no long-range order down mK. The Weiss temperature $\ensuremath{-}19.2(1)\text{ }\text{ }\mathrm{K}$, which more negative than that supports picture stronger antiferromagnetic exchange. Polarized reveals liquidlike correlations dominate this system at 3.5 K. However, below 1 K, give way intense short-range ferromagnetic length scale similar Tb-Tb nearest neighbor distance. Despite exchange, has character, stark contrast pressure-induced observed ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$.