Impurities in quasi-one-dimensional Heisenberg systems: The effect of anisotropy

The effect of small concentrations of impurities on the magnetic behavior of quasi-one-dimensional Heisenberg systems with a small orthorhombic anisotropy has been studied both theoretically and experimentally. The predicted reduction of the ordering temperature TN as a function of impurity concentration x is compared with experimental data on (CH3)2NH2Mn1-xCdxCl3 (DMMC:Cd), (CH3)2NH2Mn1-xCuxCl3 (DMMC:Cu), and CsMn1-xCuxCl3 2H2O (CMC:Cu). We also measured the magnetic phase diagram of DMMC:Cd (x=0.77%) along each of the three principal directions. The observed behavior can be qualitatively explained by the theory presented in this paper.