43 research outputs found
Structural and Magnetic Properties of [(CHâ)âNH] CuClâ2HâO
The crystal structure at room temperature and the low-temperature heat capacity and magnetic susceptibilities of single crystals of [(CH3)3 NH]CuCl3 2H2O are reported. The monoclinic crystals belong to the space group P21c with a=7.479(10), b=7.864(11), c=16.730(23), =91.98(3)°, and Z=4. The structure consists of chains of edge-sharing [CuCl4(OH2)2] octahedra running along the a axis. Each copper atom is coordinated in a square plane by two water molecules and two chlorine atoms, with two more chlorine atoms at a longer distance. The susceptibility data can be fitted adequately between 1.5 and 20°K by a CurieWeiss law [ga=2.080.01, gb=2.020.01; gc=2.110.01; a=(0.380.03)°K, b=(0.360.03)°K, c=(0.410.03)°K], but the susceptibility parallel to the chain can be better fitted as an Ising linear chain. Measurements perpendicular to the chain are not as well fitted by the Ising model. The heat capacity, which consists primarily of a lattice contribution above 3°K, begins to rise as the temperature falls below 3°K, but long-range order does not set in above 1°K, the lowest temperature attained in this work. Both Ising and Heisenberg linear-chain models fit the low-temperature data with |Jk| \u3c1°K. The results are compared with those reported for the compounds CuCl2 2H2O and CuCl2 2NC5H5. © 1972 The American Physical Society
Order to disorder transition in the XY-like quantum magnet Cs2CoCl4 induced by noncommuting applied fields
We explore the effects of noncommuting applied fields on the ground-state
ordering of the quasi-one-dimensional spin-1/2 XY-like antiferromagnet Cs2CoCl4
using single-crystal neutron diffraction. In zero field interchain couplings
cause long-range order below T_N=217(5) mK with chains ordered
antiferromagnetically along their length and moments confined to the (b,c)
plane. Magnetic fields applied at an angle to the XY planes are found to
initially stabilize the order by promoting a spin-flop phase with an increased
perpendicular antiferromagnetic moment. In higher fields the antiferromagnetic
order becomes unstable and a transition occurs to a phase with no long-range
order in the (b,c) plane, proposed to be a spin liquid phase that arises when
the quantum fluctuations induced by the noncommuting field become strong enough
to overcome ordering tendencies. Magnetization measurements confirm that
saturation occurs at much higher fields and that the proposed spin-liquid state
exists in the region 2.10 < H_SL < 2.52 T || a. The observed phase diagram is
discussed in terms of known results on XY-like chains in coexisting
longitudinal and transverse fields.Comment: revtex, 14 figures, 2 tables, to appear in Phys. Rev.