Phase Transitions in the Plane Ising Lattices Decorated with Higher Ising Spins

Multiple phase transitions in the decorated plane Ising-lattices obtained by modifying the models which have been discussed recently by several authors are investigated. The decorating spin in this paper is, so to speak, a higher Ising spin: we mean by this that the spin variable takes three or more spin values while the usual Ising spin variable takes two spin values; viz. plus and minus the unities. By this modification various types of decorated lattices of different plane Ising-lattices such as those of square, honeycomb and dice which were previously found to possess only a single transition temperature in the case of decoration with the usual Ising spins can possess three transition temperatures, if the exchange-coupling parameters are chosen appropriately. It is found in the case of decoration with the higher Ising spin that there can exist even five and seven transition temperatures in certain suitable cases.