Dynamics of K₂Ni₂(SO₄)₃ governed by proximity to a 3D spin liquid model

Quantum spin liquids (QSLs) have become a key area of research in magnetism due to their remarkable properties, such as long-range entanglement, fractional excitations, and topologically protected phenomena. Recently, the search for QSLs has expanded into the three-dimensional world, despite the suppression of quantum fluctuations due to high dimensionality. A new candidate material, K₂Ni₂(SO₄)₃, belongs to the langbeinite family and consists of two interconnected trillium lattices. Although magnetically ordered, it exhibits a highly dynamical and correlated state. In this work, we combine inelastic neutron scattering measurements with density functional theory (DFT), pseudo-fermion functional renormalization group (PFFRG), and classical Monte Carlo (cMC) calculations to study the magnetic properties of K₂Ni₂(SO₄)₃, revealing a high level of agreement between experiment and theory. We further reveal the origin of the dynamical state in K₂Ni₂(SO₄)₃ to be centred around a magnetic network composed of tetrahedra on a trillium lattice.