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.
An augmentation of the GMR is observed when decreasing the metallic layer thickness or increasing the oxide layers width suggesting this GMR is essentially an interfacial phenomenon. Moreover, ion implantation experiments were performed on such trilayers: at low doses (N⁺ ions at 150 keV for doses <10¹³ ion/cm²) improves the GMR properties of the Au-based trilayers while for higher doses the magnetoresistance drastically vanishes. In such low dose ranges the damages induced in the MLs is very low (~ 5. 10^-2 eV/at) and mostly located at interfaces. Our experiments suggest that the effect of low doses ion implantation is a slight smoothing of the interfaces which confirms the interfacial nature of the GMR.
The Pt-based system shows an additional 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.

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