Experimental Investigations of Magnetic Linear Chains

The susceptibilities and magnetizations of three different samples of FeTAC ((CH_3)_3 NH) FeCl_3cdot2H _2O.with varying amounts of deuteration have been carried out. Similar values for the exchange strengths, critical fields, and metamagnetic transitions for both the parallel and perpendicular susceptibilities were obtained for all three samples. There is an increase in the ordering temperature with increased deuteration. The values were determined to be 2.95(5), 3.00(5), 3.10(5) for FeTAC, d _5-FeTAC and d_{14 }-FeTAC, respectively. The ordering temperatures derived from the metamagnetic phase diagrams follow the same order as found by the susceptibility results. It was proposed that the effect of deuteration manifests itself only in the ferromagnetic exchange along the c-axis, causing an increase in this exchange. This causes an overall increase in the interchain exchange and the related increase of the ordering temperature. The single crystal susceptibilities and magnetizations for FeTAB, ((CH_3)_3 NH) FeBr_3 cdot 2H _2O.were studied. FeTAB is of interest due to the large decrease of the intrachain exchange as compared to that of FeTAC. An intrachain exchange strength of J/k = 5.4 K was found. The substitution of chloride by bromide causes a decrease in the intrachain exchange by a factor of 3.2. The isolation of the chains expressed as a critical ratio (kT_{rm c }/J) is 0.24 for FeTAB. This is intermediate between FeTAC (kT_{rm c} /J = 0.18) and CoTAC (kT_{rm c}/J = 0.30). Both FeTAC and FeTAB specific heats have been studied via the birefringence. FeTAC was studied along all three axes. Both the ac and bc face showed a peak reminiscent of the onset of magnetic order at 2.9 K. The FeTAC data also showed a great amount of scattering which may be the result of spinwaves. The birefringence of FeTAB showed no useful distinguishable features. The magnetic susceptibility measurements of polycrystalline samples of copper 3-methylanthranilate were reported. The data was well described by a one-dimensional S = 1/2 Heisenberg antiferromagnet model with magnetic parameters |J/k| = 1.46(3) K and g = 2.06(2). No long range ordering is evident. A discussion of the superexchange pathways and the electronic state of the bridging atoms is presented.