Crystallographic defects are always present in solid state materials. Their impact on the fluctuating spin states of magnetic insulators can be significant but is not well understood. I will present our recent results showing two interesting effects of lattice defects on spin systems. In the triangular lattice magnet KCSO, magneto-transmission measurements of the 1/3 magnetization plateau and spin supersolid phases found unusual satellite lines. We show that though these lines are sharp, they arise from disorder and enable its detailed characterization, here as dilute vacancies. In the Kitaev honeycomb model of a quantum spin liquid (QSL), odd-sided plaquettes are known to break time reversal. We propose a crystallographic "Stone-Wales" defect that is realizable geometrically and preserves QSL solvability. Its two ground state flux configurations show an observable chirality. The chiralities of distant defects couple by a ferromagnetic emergent long range interaction ~ 1/r^2.7, producing an instability to a chiral QSL at a finite critical temperature Tc set by the defect density.
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