Magnetic properties of the S = 5 2 anisotropic triangular chain compound Bi 3 FeMo 2 O 12

Competing magnetic interactions in low-dimensional quantum magnets can lead to the exotic ground state with fractionalized excitations. Herein, we present our results on an $S=\frac{5}{2}$ quasi-one-dimensional spin system ${\mathrm{Bi}}_{3}{\mathrm{FeMo}}_{2}{\mathrm{O}}_{12}$. The structure of ${\mathrm{Bi}}_{3}{\mathrm{FeMo}}_{2}{\mathrm{O}}_{12}$ consists of very well separated, infinite zigzag $S=\frac{5}{2}$ spin chains. The observation of a broad maximum around 10 K in the magnetic susceptibility $\ensuremath{\chi}(T)$ suggests the presence of short-range spin correlations. $\ensuremath{\chi}(T)$ data do not fit the $S=\frac{5}{2}$ uniform spin chain model due to the presence of second-nearest-neighbor coupling (${J}_{2}$) along with the first-nearest-neighbor coupling (${J}_{1}$) of the zigzag chain. The electronic structure calculations infer that the value of ${J}_{1}$ is comparable with ${J}_{2}$ (${J}_{2}/{J}_{1}\ensuremath{\approx}1.1$) with a negligible interchain interaction (${J}^{\ensuremath{'}}/J\ensuremath{\approx}0.01$) implying that ${\mathrm{Bi}}_{3}{\mathrm{FeMo}}_{2}{\mathrm{O}}_{12}$ is a highly frustrated triangular chain system. The absence of magnetic long-range ordering down to 0.2 K is seen in the heat-capacity data, despite a relatively large antiferromagnetic Curie-Weiss temperature ${\ensuremath{\theta}}_{CW}\ensuremath{\approx}--\phantom{\rule{0.16em}{0ex}}40$ K. The magnetic heat capacity follows nearly a linear behavior at low temperatures indicating that the $S=\frac{5}{2}$ anisotropic triangular chain exhibits the gapless excitations.