Spin-$\frac{1}{2}$ Heisenberg antiferromagnetic frustrated spin-chain systems display exotic ground states with unconventional excitations and distinct quantum phase transitions as the ratio of next-nearest-neighbor to nearest-neighbor coupling is tuned. We present a comprehensive investigation of the structural, magnetic, and thermodynamics properties of the spin-$\frac{1}{2}$ compound, $\mathrm{Cu}\text{(Ampy)ClBr}(\text{Ampy}={\mathrm{C}}_6{\mathrm{H}}_8{\mathrm{N}}_2=2$-(aminomethyl)pyridine) via x-ray diffraction, magnetization, specific heat, ${}^1\mathrm{H}$ nuclear magnetic resonance (NMR), electron spin resonance, and muon spin relaxation ($\mu \mathrm{SR}$) techniques. The crystal structure features an anisotropic triangular chain lattice of magnetic ${\mathrm{Cu}}^{2+}$ ions. Our bulk and local probe experiments detect neither long-range magnetic ordering nor spin freezing down to 0.06 K despite the presence of moderate antiferromagnetic interaction between ${\mathrm{Cu}}^{2+}$ spins as reflected by a Curie-Weiss temperature of about $-9\mathrm{K}$ from the bulk susceptibility data. A broad maximum is observed at about 9 K in magnetic susceptibility and specific-heat data, indicating the onset of short-range spin correlations. At low temperatures, the zero-field magnetic specific heat and the ${}^1\mathrm{H}$ NMR spin-lattice relaxation rate follow an exponential temperature dependence, indicating the presence of gapped magnetic excitations. Furthermore, persistent spin dynamics down to 0.088 K observed by zero-field $\mu \mathrm{SR}$ evidences lack of any static magnetism.

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• Magnetism
• Quantum spin liquid
• Specific heat
• 1-dimensional spin chains
• Electron spin resonance
• Muon spin relaxation & rotation
• Nuclear magnetic resonance