Crossover effects in weakly diluted n2 Ising antiferromagnets

Fernández [Phys. Rev. B 38, 6901 (1988)] showed that weak dilution of n2 Ising antiferromagnets generates random anisotropies. It is shown that the corresponding crossover exponent is φ=2φa-2+α, where φa is the crossover exponent for the nonrandom uniaxial anisotropy and α is the specific-heat exponent. Fernández's Monte Carlo results for n=2 in two dimensions indicate that in this special case φaγ and φγ-2β. However, the latter result is generally incorrect.