title: Incipient ferromagnetism in Tb2Ge2O7: application of chemical pressure to the enigmatic spin-liquid compound Tb2Ti2O7.
abstract: After nearly 20 years of study, the origin of the spin-liquid state in Tb2Ti2O7 remains a challenge for experimentalists and theorists alike. To improve our understanding of the exotic magnetism in Tb2Ti2O7, we synthesize a chemical pressure analog: Tb2Ge2O7. Substitution of titanium by germanium results in a lattice contraction and enhanced exchange interactions. We characterize the magnetic ground state of Tb2Ge2O7 with specific heat, ac and dc magnetic susceptibility, and polarized neutron scattering measurements. Akin to Tb2Ti2O7, there is no long-range order in Tb2Ge2O7 down to 20 mK. The Weiss temperature of -19.2(1)  K, which is more negative than that of Tb2Ti2O7, supports the picture of stronger antiferromagnetic exchange. Polarized neutron scattering of Tb2Ge2O7 reveals that liquidlike correlations dominate in this system at 3.5 K. However, below 1 K, the liquidlike correlations give way to intense short-range ferromagnetic correlations with a length scale similar to the Tb-Tb nearest neighbor distance. Despite stronger antiferromagnetic exchange, the ground state of Tb2Ge2O7 has ferromagnetic character, in stark contrast to the pressure-induced antiferromagnetic order observed in Tb2Ti2O7.
authors.affiliation: Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada.
authors.forename: A M
authors.initials: AM
authors.lastname: Hallas
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: J G
authors.initials: JG
authors.lastname: Cheng
authors.affiliation: Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: A M
authors.initials: AM
authors.lastname: Arevalo-Lopez
authors.affiliation: Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.
authors.forename: H J
authors.initials: HJ
authors.lastname: Silverstein
authors.affiliation: Jülich Centre for Neutron Science, Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstrasse 1, 85747 Garching, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Su
authors.affiliation: Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.
authors.forename: P M
authors.initials: PM
authors.lastname: Sarte
authors.affiliation: Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996-1200, USA and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4005, USA.
authors.forename: H D
authors.initials: HD
authors.lastname: Zhou
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4005, USA.
authors.forename: E S
authors.initials: ES
authors.lastname: Choi
authors.affiliation: Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: J P
authors.initials: JP
authors.lastname: Attfield
authors.affiliation: Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada and Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z7, Canada.
authors.forename: G M
authors.initials: GM
authors.lastname: Luke
authors.affiliation: Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada and Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada and Department of Chemistry, University of Winnipeg, Winnipeg, Manitoba R3B 2E9, Canada.
authors.forename: C R
authors.initials: CR
authors.lastname: Wiebe