Journal of Statistical Physics, Vol. 26, No. 4, 1981, p. 839-845.
Total spin quantum number is rigorously calculated for a quantum version of the Matfis model of random spin systems. Crossover between three universality classes of the Ising model, the XY model, and the Heisenberg model is explicitly worked out in the presence of randomness. The randomness of the type of the Mattis model is shown to have no thermodynamic effects even in quantum systems.