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

Abstract

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 (TC) 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 mT for the site dilution is always given by mT=0.0 in the whole temperature region, while the mT for the bond dilution takes a finite value below its Tc. Even in a uniformly applied transverse field, the appearance of a broad maximum in a system with site dilution can be also found, when the variation of TC is plotted as a function of r (r=J1/J, where J is the exchange interaction in inner layer and J1 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.