Synthesis and Characterization of Ba[CoSO]: Magnetic Complexity in the Presence of Chalcogen Ordering

Abstract

Barium thio-oxocobaltate(II), Ba[CoS2/2 O2/2 ], 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) Å) 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 TN =222 K 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.

Electronic physics and possible superconductivity in layered orthorhombic cobalt oxychalcogenides

“…The GGA+U calculations have also shown that with a reasonable U value, the material is in an AFM ordered state with a magnetic moment about 2.7µ B per Co atom [9]. In Fig.4, we confirm these results and plot the band structures without U and with U=3eV.…”

“…The bulk BaCoSO has been measured experimentally to be an AFM insulator [8,9]. The GGA+U calculations have also shown that with a reasonable U value, the material is in an AFM ordered state with a magnetic moment about 2.7µ B per Co atom [9].…”

Anion Ordering in Bichalcogenides

“…For tetrahedra, 3+1 and 2+2 coordinations are possible (Figure 3), of which a distorted type of the former is seen for Fe 2+ (HS, d 6 ) in AEFe 2 Ch 2 O (AE = Ba 2+ , Sr 2+ , Ch = S 2´, Se 2´) [38][39][40][41] and in CaFeSO [43]. The latter 2+2 coordination is found for TM 2+ in BaTMSO (TM = Zn 2+ [8], Co 2+ HS, d 7 [46]) and Fe 2+ (HS, d 6 ) in CaFeSeO [47]. Cis and trans 2+2 distorted square planar coordinations of two electronically noble-gas-like anions have not been reported in bulk material to date, but should be possible.…”

“…The S´O ordering in BaCoSO [46] constitutes a new type of parameter causing magnetic anisotropy (Figure 7). The extraordinary bonding situation results in two different super-exchange paths, Co´S´Co and Co´O´Co, that run parallel to two orthogonal crystallographic directions, a and c, respectively (Figure 7).…”

Spin-polarized Second Harmonic Generation from the Antiferromagnetic CaCoSO Single Crystal

“…. It has been reported that the CaCoSO is isostructural with CaZnSO, BaCoSO and CaFeSO3637383940. Since the newly synthesized CaCoSO crystallizes in non-centro-symmetry, this results in the loss of inversion symmetry, which in turn gives a considerable SHG.…”