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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 corresponds to an unusual ligand field case, are characterized by a 4A2 ground state. Average g values are in the range 2.05–2.10, while Weiss θ values are negative and increasingly so in the sequence chloro, bromo, iodo. Data are analyzed assuming axial and rhombic crystal field terms D[ S z 2 - S(S + 1)/3] and E[ S x 2 - S y 2 ] , and incorporating exchange interactions in a mean-field approximation. All D values are positive and the zero-field splitting, δ = 2(D 2 + 3E 2 ) 1 2 , increases in the order chloro, bromo, iodo, as does the size of the antiferromagnetic exchange. At low temperatures susceptibility maxima are observed, and antiferromagnetic transitions are inferred. The ratio Tc/T(χmax) 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 interchain interaction is also required. Ordering temperatures are compared with recent theory for Tc as a function of D and J for S = 3 2 antiferromagnets. Comparisons with previously studied Fe3+ systems of this general type are also made. |
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