  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 = 5/2 quasi-one-dimensional spin system Bi3FeMo2O12. The
structure of Bi3FeMo2O12 consists of very well separated, infinite zig-zag S =
5/2 spin chains. The observation of a broad maximum around 10 K in the magnetic
susceptibility suggests the presence of short-range spin correlations. Magnetic
susceptibility data do not fit to S=5/2 uniform spin chain model due to the
presence of 2nd nearest-neighbor coupling (J2) along with the 1st
nearest-neighbor coupling J1 of the zig-zag chain. The electronic structure
calculations infer that the value of J1 is comparable with J2 (J2/J1~1.1) with
a negligible inter-chain interaction (J'/J ~ 0.01), implying that Bi3FeMo2O12
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 of -40 K. The
magnetic heat capacity follows nearly a linear behavior at low temperatures
indicating that the S = 5/2 anisotropic triangular chain exhibits the gapless
excitations.
