Magnetic field induced ordering in the spin-12 chiral chain compound [Cu(pym)(H2O)4]SiF6·H2O
Physical Review B American Physical Society (APS) 112:5 (2025) 054414
Abstract:
We present single-crystal neutron diffraction, powder muon spin rotation, and pulsed-field magnetometry measurements on the Heisenberg quantum chiral chain (pym = pyrimidine), which displays a fourfold-periodic rotation of the local environment around the Cu() ions from site to site along the chain. Previous measurements on this material have shown the absence of magnetic order down to surprisingly low temperatures mK, as well as the presence of an energy gap for magnetic excitations that grows linearly with magnetic field. Here we find evidence at dilution refrigerator temperatures for a field-induced transition to long-range magnetic order above an applied magnetic field of 3 T. From the polarization of magnetic moments observed with magnetic fields applied in the direction, we can identify the static magnetic structure that best accounts for the data. The proposed model is supported microscopically by the presence of an alternating component of the tensor, which produces an internal twofold staggered field that dictates both the direction of the ordered moments and the effective coupling between adjacent chains. The observed magnetic structure is contrary to previous proposals for the departure of the magnitude and field dependence of the energy gap from the predictions of the sine-Gordon model.Spin Dynamics in the Dirac U(1) Spin Liquid YbZn2GaO5
Physical Review Letters American Physical Society (APS) 135:4 (2025) 046704
Abstract:
is a promising candidate for realizing a quantum spin liquid (QSL) state, particularly owing to its lack of significant site disorder. Pulsed-field magnetometry at 0.5 K shows magnetization saturating near 15 T, with a corrected saturation moment of after subtracting the van Vleck contribution. Our zero-field measurements down to milliKelvin temperatures provide evidence for a dynamic ground state and the absence of magnetic order. To probe fluctuations in the local magnetic field at the muon site, we performed longitudinal field experiments. These results provide evidence for spin dynamics with a field dependence that is consistent with a U1A01 Dirac quantum spin liquid as a plausible description of the ground state.A resonant valence bond spin liquid in the dilute limit of doped frustrated Mott insulators
Nature Physics Springer Nature (2025) 1-6
Electron-density analysis of halide⋯halide through-space magnetic exchange
Journal of Applied Crystallography 58:Pt 2 (2025) 363-373
Abstract:
We present a combined experimental and density functional theory study that characterizes the charge and spin density in NiX2(3,5-lutidine)4 (X = Cl, Br and I). In this material, magnetic exchange interactions occur via Ni2+-halide⋯halide-Ni2+ pathways, forming one-dimensional chains. We find evidence for weak halide⋯halide covalency in the iodine system, which is greatly reduced when X = Br and is absent for X = Cl; this is consistent with the reported 'switching-on' of magnetic exchange in the larger-halide cases. Our results are benchmarked against density functional theory calculations on [NiHF2(pyrazine)2]SbF6, in which the primary magnetic exchange is mediated by F-H-F bridging ligands. This comparison indicates that, despite the largely depleted charge density found at the centre of halide⋯halide bonds, these through-space interactions can support strong magnetic exchange gated by weak covalency and enhanced by significant electron density overlapping that of the transition metal centres.Magnetic properties of a staggered S=1 chain with an alternating single-ion anisotropy direction
Physical Review B American Physical Society (APS) 111:1 (2025) 014421