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 CIP-GMR. 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.