THERMAL VARIATION OF THE MAGNETORESISTANCE OF SOFT SPIN-VALVE MULTILAYERS

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 DELTA-R/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 up and spin down intermixing in the ferromagnetic layers.