We report x-ray diffraction, magnetic susceptibility, heat capacity, 1 H nuclear magnetic resonance (NMR), and muon spin relaxation (µSR) measurements, as well as density-functional band-structure calculations for the frustrated S = 3/2 triangular lattice Heisenberg antiferromagnet (TLHAF) α-HCrO2 (trigonal, space group: R 3m). This compound undergoes a clear magnetic transition at TN ≃ 22.5 K, as seen from the drop in the muon paramagnetic fraction and concurrent anomalies in the magnetic susceptibility and specific heat capacity. Local probes (NMR and µSR) reveal a broad regime with slow fluctuations down to 0.7 TN, this temperature corresponding to the maximum in the µSR relaxation rate and in the NMR wipe-out. From the comparison with NaCrO2 and α-KCrO2, the fluctuating regime and slow dynamics below TN appear to be hallmarks of the TLHAF with ABC stacking. We discuss the role of interlayer frustration which may bear implications to recent spin-liquid candidates with the triangular geometry.
We report synthesis and magnetic properties of quasi-one-dimensional spin-12 Heisenberg antiferromagnetic chain compound BaNa2Cu(VO4)2. This orthovanadate has a centrosymmetric crystal structure, C2/c, where the magnetic Cu2+ ions form spin chains. These chains are arranged in layers, with the chain direction changing by 62∘ between the two successive layers. Alternatively, the spin lattice can be viewed as anisotropic triangular layers upon taking the interchain interactions into consideration. Despite this potential structural complexity, temperature-dependent magnetic susceptibility, heat capacity, electron spin resonance intensity, and nuclear magnetic resonance (NMR) shift agree well with the uniform spin-1/2 Heisenberg chain model with an intrachain coupling of J/kB≃5.6 K. The saturation field obtained from the magnetic isotherm measurement consistently reproduces the value of J/kB. Further, the 51V NMR spin-lattice relaxation rate mimics the one-dimensional character in the intermediate temperature range, whereas magnetic long-range order sets in below TN≃0.25 K. The effective interchain coupling is estimated to be J⊥/kB≃0.1 K. The theoretical estimation of exchange couplings using bandstructure calculations reciprocate our experimental findings and unambiguously establish the onedimensional character of the compound. Finally, the spin lattice of BaNa2Cu(VO4)2 is compared with the chemically similar but not isostructural compound BaAg2Cu(VO4)2.
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