ORDER-DISORDER TRANSITION IN AN EXTERNAL-FIELD IN RANDOM FERROMAGNETSAND NEMATIC ELASTOMERS

We study theoretically the effect of external field on random anisotro py ferromagnets and nematic elastomers. The system evolves on increasi ng field from the correlated spin glass state to the aligned ferromagn etic state via a first order phase transition at a threshold field acc ompanied by a significant jump of the average magnetization. The mean magnetization growth is due to reorientation, rather than growth of in dividual domains. We discuss the additional hardening mechanisms in ne matic elastomers that increase the threshold of the transition observe d experimentally and lead to the ''fossil'' domain walls left in the a ligned system.