The discovery of antiferromagnetic interlayer coupling[1] and giant magnetoresistance[2] in Fe-Cr superlattices and sandwiches raises a number of challenging questions, both experimental and theoretical. Recently several models for the interlayer coupling[3,4] and magnetoresistance[3,5] have been put forward, but so far detailed experimental tests of these models are lacking. In particular, the role of the various carrier scattering mechanisms (phonon, impurity, spin-wave, etc.) in the magnetoresistance is still unclear. Because these scattering processes vary differently with temperature, measurement of the temperature dependence of the magnetoresistance may give some insight into its microscopic origin.
The temperature and field dependences of the resistance were measured on both single-crystal and polycrystalline Fe-Cr-Fe sandwiches. The single-crystal samples, which have been described previously,[6] were grown by molecular-beam epitaxy (MBE) on ZnSe (100) epilayers on GaAs substrates. The polycrystalline samples were evaporated at a rate of 2Å/second onto glass substrates held at about 200 °C. Fe films made by evaporation have a (110) texture according to x-ray diffraction, but magnetization and angle-dependent ferromagnetic resonance measurements show that they have an in-plane magnetic anisotropy of only a few Oe. On both sets of samples, data were taken with the magnetic field applied in the film plane, using a dc current of about 100 mA.