Abstract :
We study numerically the zero temperature Random Field Ising Model on cubic lattices of various linear sizes 6≤L≤90 in three dimensions with the purpose of verifying the validity of universality for disordered systems. For each random field configuration we vary the ferromagnetic coupling strength J and compute the ground state exactly. We examine the case of different random field probability distributions: Gaussian distribution, zero width bimodal distribution hi=±1, wide bimodal distribution hi=±1+δh (with a Gaussian δh). We also study the case of the randomly-diluted antiferromagnet in a field, which is thought to be in the same universality class. We find that in the infinite volume limit the magnetization is discontinuous in J and we compute the relevant exponent, which, according to finite size scaling, equals 1/ν. We find different values of ν for the different random field distributions, in disagreement with universality.
