MAGNETORESISTANCE OF PARAMAGNETIC METALLIC LAYERS SANDWICHED BETWEEN FERROMAGNETIC LAYERS

Experimental results on magnetoresistance of Fe/Cr/Fe trilayers and multilayers show a large enhancement of this magnitude for a thickness of approximately 10 layers and decreases exponentially with the number of layers. In this work it is proposed that the key point to understand these experiments may lay in the fact that the exchange field of the ferromagnets penetrates in the paramagnet as has recently been proposed by the authors to explain coupling energies in trilayers. Even if the decay length of the penetrating field is small, of the order of nearest neighbors in Fe, its magnitude is large (1000 T), larger than any applied saturation field. The ferromagnetic and antiferromagnetic configurations give rise to two different field configurations and therefore to two different values of the resistance. In the opinion of the authors this is controlled by the effective section that the electrons can go. Also, it is not doubtful that the magnetoresistance is large but that the magnetic field (scattering spin potential) that the electrons see is large. It is found that the magnetoresistance is very much structure or roughness dependent and increases, in first approximation, with its amplitude. The magnetoresistance depends exponentially with the number of paramagnetic layers with a 10-20-angstrom decay length, but does not oscillate; it is a smooth function.