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${}_7$.

6 pages, 4 figures, accepted for publication in PRL

References in corpus (9)

• Dynamically-Induced Frustration as a Route to a Quantum Spin Ice State in Tb2Ti2O7 via Virtual Crystal Field Excitations and Quantum Many-Body Effects
• Lightly stuffed pyrochlore structure of single-crystalline Yb2Ti2O7 grown by the optical floating zone technique
• Structural Fluctuations in the Spin Liquid State of Tb2Ti2O7
• Field Induced Order and Spin Waves in the Pyrochlore Antiferromagnet Tb2Ti2O7
• Antiferromagnetic Spin Ice Correlations at (1/2,1/2,1/2) in the Ground State of the Pyrochlore Magnet Tb2Ti2O7
• Investigation of the magnetic fluctuations in Tb${}_2$Sn${}_2$O${}_7$ ordered spin ice by high resolution energy-resolved neutron scattering
• Crystal Field and Magnetoelastic Interactions in Tb2Ti2O7
• Field-Induced magnetic structures in Tb2Ti2O7 at low temperatures: From spin-ice to spin-flip structures
• Low temperature dynamic freezing and the fragility of ordering in Tb2Sn2O7

Cited by in corpus (3)

• Magnetic Frustration in Lead Pyrochlores
• 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
• Intertwined Magnetic Dipolar and Electric Quadrupolar Correlations in the Pyrochlore Tb${}_2$Ge${}_2$O${}_7$