DILUTED QUASI-ONE-DIMENSIONAL CLASSICAL ANTIFERROMAGNETS

We consider the effect of the exchange disordering, mainly the nonmagn etic dilution, on the low-temperature properties of the quasi-one-dime nsional classical antiferromagnets. Dynamic susceptibility expansion i n defect concentration shows that even a low level of doping substanti ally changes the spin-wave stiffness and the transverse susceptibility . We investigate the nonperturbative concentration dependencies of the spin-wave velocities and susceptibility arising when the impurity con centration exceeds the small characteristic value x0 = square-root J(p erpendicular-to)/J(parallel-to). A general result, pertinent to the tr ue three-dimensional antiferromagnets as well, concerns the excitation spectrum of the disordered nonfrustrated antiferromagnets with nonflu ctuating anisotropy. In this case the hydrodynamical description of lo ng-wave excitations breaks down, and the spin waves with energies near the anisotropy gap are overdamped.