The influence of sublayer thickness on GMR and magnetisation reversal in permalloy/Cu multilayers

It has been shown that in Py/Cu (Py = Ni87Fe17, permalloy) multilayers obtained by face-to-face sputtering technology, two well-separated antiferromagnetically coupled ranges can be found centered at d(Cu) approximate to 1 and 2 nm, respectively, However, d(Cu) values corresponding to the largest field sensitivity of the GMR effect are different from those for which the strongest antiferromagnetic exchange coupling has been found. With decreasing Py thickness, the magnetic properties become strongly influenced by the magnetisation fluctuations, We attribute this effect to the presence of compositionally intermixed interfaces. Changes in the magnetic properties and magnetoresistance as a function of Py thickness are analysed in terms of evolution from paramagnetic through superparamagnetic to ferromagnetic behaviour of these intermixed regions.