MAGNETISM IN BACOS2

BaCoS2 is a layered Mott-Hubbard insulator that orders antiferromagnet ically near 300 K. We report magnetic susceptibility measurements on p olycrystalline BaCoS2 from 77 to 800 K, and in- and out-of-plane measu rements on single crystals from 2 to 350 K. We also report a powder ne utron refinement of the magnetic structure of BaCoS2. The neutron meas urements indicate that the moments lie in the plane, and that the magn etic unit cell is the same as the (orthorhombic) chemical cell. The or dered moment obtained from the neutron refinement is close to 3 mu(B), indicating that the Co ions are in the high-spin (S = 3/2) configurat ion. The effective moment inferred from the high temperature susceptib ility, p = 5.26 mu(B), is also consistent with high-spin Co+2. (C) 199 7 American Institute of Physics.