Glassy correlated state induced by disorder in the frustrated antiferromagnet Tb₂Zr₂O₇

We study the low-temperature thermomagnetic properties of the polycrystalline material Tb₂Zr₂O₇ through ac susceptibility and specific heat measurements. This zirconate displays a defect-fluorite structure in which the magnetic Tb³⁺ and nonmagnetic Zr⁴⁺ cations sit randomly on the same metal sublattice. No long-range magnetic order is found down to 100 mK, although dominant antiferromagnetic interactions are observed and the spins remain dynamic down to the lowest temperatures investigated. We observed a frequency-dependent peak around 2.5 K which is well described by many models of a canonical spin-glass transition. In-field specific heat measurements and the recovered entropy of the system Rln(4) suggest a two doublets ground state separated by 7 K. Comparisons to the pyrochlores Tb₂Ti₂O₇ and Tb₂Hf₂O₇ reinforce the collective spin-glass-type behavior and the opening for discussions of an exotic Coulomb phase in this material.