STRONG MAGNETORESISTANCE REDUCTION AT THE COERCIVE-FIELD CROSSOVER OF 2 UNCOUPLED MAGNETIC-FILMS

The variation of the magnetoresistance (MR) with temperature T in the range 1.4-300 K has been studied in three dissymmetric structures Au/M1/Au/M2/Au where M1 and M2 are two ultrathin films of either Co or Fe with perpendicular anisotropy. In the Fe sample, the low-temperature MR is 7.6%, showing for the first time the spin-valve effect in this system. In all samples, the variation of the coercive fields H(c1) and H(c2) vs T exhibits a crossover leading to a reduction by a factor one-half of the MR at the same temperature. The fit of the MR curves versus T in the frame of the Camley-Barnas model leads to the values of the electron mean-free-path and spin-dependent transmission coefficients at the interfaces in these samples.