The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an effective XXZ chain. The data exhibit universal scaling behavior in the vicinity of H(c1) and H(c2), indicating that the system is near a quantum critical point.

Mixed organic/inorganic Langmuir−Blodgett (LB) films have been prepared in which the polar network is a manganese phosphonate continuous lattice and the organic network contains a substituted tetrathiafulvalene amphiphile. The bis(phosphonic acid) amphiphile, 2,3-bis[(4‘-phosphonobutyl)thio]-6,7-bis(tetradecylthio)tetrathiafulvalene, 1, has been synthesized and deposited from an aqueous Mn2+ subphase to form Y-type LB films with stoichiometry Mn2(1)(H2O)2. Since the amphiphile is a bis(phosphonate), the inorganic network forms the Mn(O3PR)H2O structure known in other manganese phosphonate LB films and layered solids. The film becomes magnetic near 11.5 K when the manganese phosphonate network orders as a canted antiferromagnet. Attempts to subsequently oxidize the tetrathiafulvalene (TTF) network did not result in stable phases. Structural characterization was aided by the synthesis of a solid-state manganese bis(phosphonate) model compound, Mn2(2)(H2O)2, where 2 is the ligand 2,3-bis[(2‘-phosphonoethyl)thio]-6,7-bis(methylthio)tetrathiafulvalene.

Catena(dimethylammonium-bis(mu2-chloro)-chlorocuprate), (CH3)2NH2CuCl3, forms chains of Cu2Cl6(2-) bifold dimers linked along the structural chain axis by terminal chlorides forming long semicoordinate bonds to adjacent dimers. The structural chains are separated by dimethylammonium ions that hydrogen bond to chloride ions of the dimers. A structural phase transition below room temperature removes disorder in the hydrogen bonding, leaving adjacent dimers along the chain structurally and magnetically inequivalent, with alternating ferromagnetic and antiferromagnetic pairs. The coupled dimers are magnetically isolated from each other along the structural chain axis by the long semicoordinate Cu-Cl bond. However, the dimers couple to like counterparts on adjacent chains via nonbonding Cl...Cl contacts. The result is two independent magnetic chains, one an alternating antiferromagnetic chain and the other an antiferromagnetic chain of ferromagnetically coupled copper dimers, which run perpendicular to the structural chains. This magnetostructural analysis is used to fit unusual low-temperature (1.6 K) magnetization vs field data that display a two-step saturation. The structural phase transition is identified with neutron scattering and capacitance measurements, and the X-ray crystal structures are determined at room temperature and 84 K. The results appear to resolve long-standing confusion about the origins of the magnetic behavior of this compound and provide a compelling example of the importance of two-halide magnetic exchange.

Commensurate spin slip structures were observed by Gibbs et al. in X-ray scattering studies. We have observed magnetic transitions in macroscopic measurements of magnetization, AC susceptibility, electrical resistivity, and thermal expansivity along the three crystal axes of single-crystal erbium that correspond to these spin slip structures. Our measurements show antiferromagnetic ordering of the c axis and basal plane components at TN//=89 K and TN perpendicular to =53 K, respectively, as well as ferromagnetic ordering along the c axis below 18 K. In addition, we observe anomalies at 27, 29, 34, 40 and 51 K. These anomalies correspond well with previous studies. The order of these transitions can be determined using thermal expansion data. We observe anomalies at 21.6 K and 23.3 K that we believe correspond to basal plane recording in the 2(44) magnetic phase. There are also anomalies above TN perpendicular to suggesting a short-range ordering of the basal plane moments. We have analysed the resistivity versus temperature plot in the ferromagnetic region to determine the temperature dependence and the spin wave activation energy along the b and c axes.

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