Dynamic and frozen quantum magnetism in the ground states of triangular lattice magnets YbMgGaO₄, ErMgGaO­₄ and YbCoGaO₄ from inelastic neutron scattering

The putative quantum spin liquid (QSL) state exhibited by YbMgGaO₄ is largely ascribed to the quasi-2D triangular lattice which the magnetic Yb³⁺ moments decorate in concert with anisotropic exchange and disorder in neighbouring disordered Mg²⁺/Ga³⁺ bilayers [1,2,3]. We present new inelastic neutron scattering (INS) measurements on YbMgGaO₄ as well as its isostructural sister compounds: ErMgGaO₄ and YbCoGaO₄. Each material was synthesized as a phase-pure powder and INS measurements were performed on IN6-Sharp with E_i = 3.1 meV at the Institut Laue-Langevin. We discuss the observed hallmarks of a QSL in YbMgGaO₄ and contrast these with signatures of frozen spin correlations in each of ErMgGaO₄ and YbCoGaO₄ in the INS measurements. The case of YbCoGaO4 is an interesting one as it displays the interplay between a QSL-like state associated with the Yb³⁺ magnetism, interleaved with a two-dimensional spin glass state originating from the disordered Co²⁺ magnetism. 

[1] Paddison, J., Daum, M., Mourigal, M. et al. Nature Phys 13, 117–122 (2017)

[2] Li, Y., Adroja, D., Zhang, Q. et al. Phys. Rev. Lett. 118, 107202 (2017)

[3] Zhu, Z., Maksimov, P. A., Chernyshev, A. L. et al. Phys. Rev. Lett. 119, 157201 (2017)