Spin-wave excitations and perpendicular susceptibility of a diluted antiferromagnet near percolation threshold

Abstract

The long-wavelength excitations of a diluted antiferromagnet near the percolation threshold p_c are studied. Within the hydrodynamic theory, the excitation frequency depends on two parameters, A and χ_t. A is the stiffness associated with the spatial variation in the staggered magnetization and χ_t is the perpendicular susceptibility in the ordered state of the antiferromagnet. The critical behavior of A near p_c is known. We develop a field-theoretic formalism to calculate χ_t. We ex- plicitly calculate χ_t in the mean-field approximation and find that it diverges as ||ln(p-p_c)||, as the concentration p approaches p_c. Some further scaling arguments yield a scaling relation relating the divergence exponent of χ_t with other known exponents at the percolation critical point.