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

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${}_7$.

arXiv comment6 pages, 4 figures, accepted for publication in PRL

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Cited by in corpus (10)

• Theory of multiple--phase competition in pyrochlore magnets with anisotropic exchange, with application to Yb2Ti2O7, Er2Ti2O7 and Er2Sn2O7
• Living on the edge : ground-state selection in quantum spin-ice pyrochlores
• Magnetic Frustration in Lead Pyrochlores
• Competing spin liquids and hidden nematic order in spin ice with frustrated transverse exchange
• Sensitivity of magnetic properties to chemical pressure in lanthanide garnets $L{n}_3{A}_2{X}_3{\text{O}}_{12}$, $Ln$ = Gd, Tb, Dy, Ho, $A$ = Ga, Sc, In, Te, $X$ = Ga, Al, Li
• XY Antiferromagnetic Ground State in the Effective S=1/2 Pyrochlore Yb2Ge2O7
• Spinon walk in quantum spin ice
• Traversing the pyrochlore stability diagram; microwave-assisted synthesis and discovery of mixed B-site Ln${}_2$InSbO${}_7$ family
• Intertwined Magnetic Dipolar and Electric Quadrupolar Correlations in the Pyrochlore Tb${}_2$Ge${}_2$O${}_7$
• Crossover between tricritical and Lifshitz points in pyrochlore FeF${}_3$