The effect of sub-lattice order in binary alloys with one magnetic components. I

An alloy with mole-fractions c A of component A with magnetic spin quantum number s and c B=1-c A of a non-magnetic component B is considered for general s and c A when the interaction energies favour the development of sub-lattice order of the 1–1 type among the A and B atoms. Using the zeroth-order statistical approximation and interaction energies of arbitrary range the Helmholtz free energy is minimized with respect to the A–B long-range order parameter and the magnetizations of the two sub-lattices and the conditions for ordering and magnetic transitions are discussed. The effects of A-B order on the Curie or Néel point curves and of permanent magnetization on the critical ordering temperatures are considered. In spite of the assumption of a constant magnetic moment on each A atom the mixture may behave in a variety of ways as c A changes. In particular, depending on the lattice structure and the range of the exchange interactions between A atoms, A–B order may either inhibit or enhance the magnetic transitions which would take place in its absence.