We report proximate quantum spin liquid behavior in K2Co2(SO4)3 with the magnetic Co2+ ions embedded on a highly frustrated three-dimensional double trillium lattice. Single-crystal and high-resolution synchrotron powder x-ray diffraction experiments reveal a structural phase transition at Tt≃125 K from high-temperature cubic to low-temperature monoclinic phase with the three-fold superstructure. Magnetization and heat capacity consistently show the formation of the Jeff=1/2 state of Co2+ below 50 K. In zero field, K2Co2(SO4)3 shows signatures of static magnetic order formed below T∗≃0.6 K, but muon spin relaxation experiments reveal a large fluctuating component that persists down to at least 50 mK, reminiscent of quantum spin liquid (QSL). Static order is completely suppressed in the small magnetic field of ∼1 T, and low-temperature heat capacity demonstrates the T2 behavior above this field, another fingerprint of QSL. Ab initio calculations show a competition of several antiferromagnetic couplings that render K2Co2(SO4)3 a promising pseudospin-21 material for studying quantum magnetism in the double trillium lattice geometry.
@article{arxiv.2508.07687,
title = {Proximate spin-liquid behavior in the double trillium lattice antiferromagnet K$_2$Co$_2$(SO$_4$)$_3$},
author = {A. Magar and K. Somesh and M. P. Saravanan and J. Sichelschmidt and Y. Skourski and M. T. F. Telling and V. A. Ginga and A. A. Tsirlin and R. Nath},
journal= {arXiv preprint arXiv:2508.07687},
year = {2025}
}