Navegando por Autor "Vieira, Selma R."
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Artigo Effects of composition on the stability of the magnetic order of ferrimagnetic multilayers(APS PHYSICS, 2002) Dantas, Ana L.; Vieira, Selma R.; Carriço, Artur da SilvaWe study the field induced instability of the antiferromagnetic phase of magnetic multilayers consisting of a stacking of uniaxial ferromagnetic films, F1 and F2, with thicknesses t1 and t2, coupled through a nonmagnetic ~NM! spacer. The external field is along the uniaxial axis, in the plane of the films, and the composition is varied by choosing arbitrary values of the relative thickness b5t1 /t2. We calculate the critical value of the external field H*, and examine the nature of the phase transition. We find that H* does not change with the multilayer thickness in the case of multilayers with an even number of magnetic layers, (@F1 /NM/F2 /NM#n , n arbitrary!. The nature of the phase transition and the critical field depend on the value of b, and the minimum value of H* corresponds to b51. For a multilayer with an odd number of magnetic layers we find that the thickness dependence of the critical field is significantly affected by the value of b.Artigo Soft mode of antiferromagnetic multilayers near the surface spin-flop transition(Physical review B, 2005) Dantas, Ana L.; Vieira, Selma R.; Almeida, N. S.; Carriço, Artur da SilvaWe investigate the long wavelength soft mode of antiferromagnetic (AF) multilayers near the field induced instability of the AF order. We show that in the vicinity of the surface spin flop field sHSSFd the frequency of the lowest mode is V2 /g2=asHSSF−Hd+bsHSSF−Hd2, where a and b are functions of the magnetic parameters of the multilayer and H is the external field strength. For antiferromagnetic films the first order term is zero (due to the absence of demagnetizing effects) and b=1.