Thermal Variation of the Magnetoresistance of Soft Spin-Valve Multilayers

Abstract

We have measured the thermal variation of the magnetoresistance of several series of soft spin-valve structures TM1/NM/TM2/antiferromagnet between 77 K and 350 K. TM1 and TM2 are ferromagnetic transition metals or their alloys (Co, Ni, Ni₈₀Fe₂₀), the magnetization of TM2 is constrained by exchange coupling to an antiferromagnet, NM is Cu or Au. We show that the amplitude of the spin-valve effect (magnetoresistance ΔR/R due to the change in relative orientation of the magnetizations of adjacent ferromagnetic layers) decreases almost linearly with temperature. An exponential decrease of the spin-valve amplitude is found vs. the thickness of the noble-metal interlayer with a characteristic decay length nearly independent of temperature. Consequently, we demonstrate that the thermal decrease of the magneto-resistance of these structures is not due to increased scattering in the noble-metal spacer, but mainly to spin ↑ and spin ↓ intermixing in the ferromagnetic layers.