Low-temperature excitations in random two-dimensional antiferromagnets

A numerical method involving the time integration of equations of motion is developed for calculating response functions of antiferromagnets. The method is particularly useful in calculating dynamic response functions S(k, omega ) and can also be used to obtain densities of states. The technique is applied to the two-dimensional random antiferromagnets Rb 2 Mn 0.5 Ni 0.5 F 4 and Rb 2 Mn c Zn 1-c F 4 . In the former case, good agreement is found with the recently measured S(k, omega ) and in the latter some interesting clustering effects that should be accessible experimentally are found.