New disordered phase of a ferromagnetic binary Ising system.

The phase diagrams and the temperature (or field) dependences of magnetizations in a binary Ising ferromagnetic alloy consisting of spin-1/2 and spin-1 components with a crystal-field interaction are investigated by the use of an effective-field theory with correlations. We find a new disordered phase in which the transition temperature (or magnetization) reduces to zero when the crystal-field interaction takes a large negative value. The magnetization process in the new disordered phase is examined. We find that it exhibits phenomena similar to, but with important differences from, those of metamagnets, even though all the exchange interactions have a positive sign.