MAGNETIC-PROPERTIES OF FE[S2CNC4H8O](2)X,X=CL,BR,I

The title systems, including solvated and unsolvated forms, have been studied by dc susceptibility measurements. Curie-Weiss fits show that all materials except the unsolvated chloro system, which probably corr esponds to an unusual ligand field case, are characterized by a (4)A(2 ) ground state. Average g values are in the range 2.05-2.10, while Wei ss theta values are negative and increasingly so in the sequence chlor o, bromo, iodo. Data are analyzed assuming axial and rhombic crystal f ield terms D[(S) over cap(z)(2)-S(S + 1)/3] and E[(S) over cap(x)(2)-( S) over cap(y)(2)], and incorporating exchange interactions in a mean- field approximation. All D values are positive and the zero-field spli tting, delta = 2(D-2 + 3E(2))(1/2), increases in the order chloro, bro mo, iodo, as does the size of the antiferromagnetic exchange. At low t emperatures susceptibility maxima are observed, and antiferromagnetic transitions are inferred. The ratio T-c/T(chi(max)) suggests that some systems are of low magnetic dimensionality. Fits based on 2D-XY or 1D -Ising models are presented; in each case a strong interlayer or inter chain interaction is also required. Ordering temperatures are compared with recent theory for T-c as a function of D and J for S = 3/2 antif erromagnets. Comparisons with previously studied Fe3+ systems of this general type are also made.