Experimental evidence of the spin-dependence of electrons reflections in magnetic multilayers

The giant magnetoresistance (GMR) of multilayers in the current in plane (CIP) geometry can be understood by considering the spin-dependent scattering effects within the magnetic layers and at the non-magnetic/magnetic interfaces. In this paper we experimentally put on view the magnetoresistance effect created only by the spin-dependent reflection of electrons at the interfaces. Two epitaxial systems were studied, consisting of two ferrimagnetic insulators layers at low temperature (CoFe2O4 and Fe3O4) separated by a non-magnetic metallic layer (M = Au or Pt). The transport properties indicate that conduction of the CoFe2O4/M/Fe3O4 trilayers take place within the thin metallic layer. An optimal magnetoresistance up to 5% at 10 K associated to the switching from parallel to anti-parallel configuration of the magnetization of the two ferrite layers has been obtained. It is associated to the spin-dependent interfacial scattering contribution of the CIPGMR. The augmentation of the GMR when decreasing the metallic layer thickness or increasing the oxide layers width confirms this GMR is essentially an interfacial phenomenon. The Pt-based system shows an additional Anisotropic Magnetoresistance (AMR), which is not evidenced in the Au-based trilayer. We suggest that this AMR comes from the polarization of the Pt layer by the ferrimagnetic oxides.