eng Science and Education Publishing International Journal of Physics 2333-4576 2018-10-07 6 5 147 154 10.12691/ijp-6-5-2 IJP2018652 article A. Waddahou 1 M. Chahid mustapha.chahid@gmail.com 1 A. Maarouf 1 Polymer Physics and Critical Phenomena Laboratory, Sciences Faculty Ben M'sik, Hassan II University of Casablanca, P. O. Box 7955, Casablanca, Morocco The aim of this paper is to determine the full order parameter profiles close to the surface for a system made of two strongly coupled paramagnetic sublattices of respective moments and . The material exhibits a para-ferrimagnetic transition at some critical temperature Tc greater than the room temperature. The free energy describing the physics of the system is of Landau type, and involves, beside quadratic and quartic terms in both and , a lowest-order coupling, -Co where Co<0 is the coupling constant measuring the interaction between the two sublattices. We consider here below a film of thickness L, and the free energy is then a sum of bulk and surface contributions expanded in terms of the local order parameters. The magnetization at the surface are s and s. As in a recent paper (whom the present work is an extension), we first reduce the model to an effective 4 -theory written in terms of the overall magnetization =+ and the associated fraction of magnetization a=/(+). For the ordinary transition where the extrapolation length is positive s>0, we determine the order parameter profile near surfaces. We show, in particular, that the magnetization behavior is governed, in addition of s and the bulk correlation length b-, by a new length La. We have interpreted this latter as the width of the ordered ferrimagnetic layer close to the surface. Finally, we examine the extraordinary (s<0), special (s=) and surface (at Tcs>Tc) transitions. http://pubs.sciepub.com/ijp/6/5/2/ijp-6-5-2.pdf sublattices coupling paramagnetism ferrimagnetism transition order parameter profiles