Observation of a gapped phase in the one-dimensional (Formula presented) Heisenberg antiferromagnetic chain Cu(Ampy)ClBr

Spin- (Formula presented) 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- (Formula presented) compound, Cu(Ampy)ClBr (Ampy = C6H8N2 = 2-(aminomethyl)pyridine) via x-ray diffraction, magnetization, specific heat, ¹H nuclear magnetic resonance (NMR), electron spin resonance, and muon spin relaxation (μSR) techniques. The crystal structure features an anisotropic triangular chain lattice of magnetic Cu²⁺ 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 Cu²⁺ spins as reflected by a Curie-Weiss temperature of about −9 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 ¹H 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 μSR evidences lack of any static magnetism.

Duke Scholars

Author Sara Haravifard Physics