Phase diagrams in a ultra-thin transverse Ising film with bond or site dilution at surfaces

The phase diagrams and magnetizations of two nanoscaled thin films with bond and site dilutions at the surfaces, described by the transverse Ising model, are investigated by the use of the effective field theory with correlations. Some characteristic phenomena have been found in them; The transition temperature (T-C) of bond dilution is always larger than the corresponding one of site dilution. There exists some region in the phase diagram where the longitudinal magnetization m(T) for the site dilution is always given by m(T) = 0.0 in the whole temperature region, while the m(T) for the bond dilution takes a finite value below its Tc. Even in a uniformly applied transverse field, the appearance of abroad maximum in a system with site dilution can be also found, when the variation of T-C is plotted as a function of r(r = J(1)/J, where J is the exchange interaction in inner layer and J(1) is the exchange interaction between the surface and the next inner layer). But, such a phenomenon cannot be obtained in the system with bond dilution. (C) 2013 Elsevier B.V. All rights reserved.