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Abstract:
Barium thio-oxocobaltate(II), Ba[CoS2/2O2/2], was synthesized by the
reaction of equimolar amounts of BaO, Co, and S in closed silica
ampoules. The title compound (Cmcm, a=3.98808(3), b=12.75518(9),
c=6.10697(4)angstrom) is isostructural to Ba[ZnSO]. The use of soft
X-ray absorption spectroscopy confirmed that cobalt is in the oxidation
state +2 and tetrahedrally coordinated. Its coordination consists of two
sulfur and two oxygen atoms in an ordered fashion. High-temperature
magnetic susceptibility data indicate strong low-dimensional spin-spin
interactions, which are suggested to be closely related to the
layer-type crystal structure and perhaps the ordered distribution of
sulfur and oxygen. Antiferromagnetic ordering below T-N=222K is observed
as an anomaly in the specific heat, coinciding with a significant
lowering of the magnetic susceptibility. Density functional theory
calculations within a generalized-gradient approximation (GGA)+U
approach identify an antiferromagnetic ground state within the
square-like two-dimensional layers of Co, and antiferromagnetic
correlations for nearest and next nearest neighbors along bonds mediated
by oxygen or sulfur. However, this magnetic state is subject to
frustration by relatively strong interlayer couplings.
