The susceptibility of DMMC;Cd: A dilute 1d anisotropic Heisenberg system

The susceptibility of (CH₃)₂NH₂Mn _1-xCd_xCl₃, a good quasi-1d Heisenberg system, has been measured along the three principal crystallographic directions for 1.5<T<4.2K and x=0.067. The experimental data are compared successively with the susceptibility of the exactly soluble isotropic Heisenberg chain, the predictions based on numerical calculations of a Heisenberg chain with orthorhombic anisotropy, and a newly developed short-chain approximation. The effective anisotropy per spin is found to decrease by dilution, which is supported by measurement of the spin-flop transition field versus temperature for x=0.004 and 0.008.