Disorder-driven magnetic duality in the spin-$\frac{1}{2}$ system ktenasite, Cu$_\text{2.7}$Zn$_\text{2.3}$(SO$_\text{4}$)$_\text{2}$(OH)$_\text{6}\cdot$6H$_\text{2}$O

Abstract

Disorder in frustrated quantum systems can critically influence their magnetic ground states and drive exotic correlated behavior. In the $S = \frac{1}{2}$ system ktenasite, Cu$_\text{2.7}$Zn$_\text{2.3}$(SO$_\text{4}$)$_\text{2}$(OH)$_\text{6}\cdot$6H$_\text{2}$O, we show that structural disorder drives an unexpected dimensional crossover and stabilizes a rare coexistence of distinct magnetic states. Neutron diffraction reveals significant Cu/Zn mixing at the Cu2 site, which tunes the Cu$^{2+}$ sublattice from a two-dimensional scalene-distorted triangular lattice into a one-dimensional spin-chain network. Magnetic susceptibility, neutron diffraction, ac susceptibility, and specific heat measurements collectively indicate magnetic duality: a coexistence of incommensurate long-range magnetic order below $T_\text{N} = 4\,$K and a cluster spin-glass state with $T_\text{f} = 3.28\,$K at $\nu = 10\,$Hz. Our findings highlight ktenasite as a rare platform where structural disorder tunes the effective dimensionality and stabilizes coexisting ordered and glassy magnetic phases, offering a unique opportunity to explore the interplay of frustration, disorder, and dimensional crossover in quantum magnets.