We have carried out an experimental and theoretical study of the magnetoresistance MR(H) in the CPP (current perpendicular to the planes) mode for two types of magnetic multilayers that differ only in the ordering of the magnetic layers: [Co(10 A)/Cu(200 A)/Co(60 A)/Cu(200 A)](N) and [Co(10 A)/Cu(200 A)](N)[Co(60 A)/Cu(200 A)](N). The series resistor model predicts that in the CPP mode MR(H) is independent of the ordering of the layers. Nevertheless, the measured MR(H) curves were found to be completely different for the two cases. Calculations based on a realistic band structure and the Kubo formula show that the results are a consequence of a long mean free path.

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Low-energy visible light (LEVL) has previously been found to modulate various processes in different biological systems. One explanation for the stimulatory effect of LEVL is light-induced reactive oxygen species formation. In the present study, both sperm and skin cells were illuminated with LEVL and were found to generate singlet oxygen (1O2). The detection of 1O2 was performed using a trapping probe, 2,2,6,6-tetramethyl-4-piperidone, coupled with electron paramagnetic resonance spectroscopy. In addition, we have shown that, together with O2 generation, LEVL illumination increases the reductive capacity of the cells, which explains the difficulties encountered in 1O2 detection. The potential of visible light to change the cellular redox state may explain the recently observed biostimulative effects exerted by LEVL.

We have measured the field dependence of the magnetoresistance MR(H) in the CPP mode for two types of magnetic multilayers that differ only in the ordering of the magnetic layers: [Co (10 Å)/Cu/Co (60 Å)/Cu]N and [Co (10 Å)/Cu]N [Co (60 Å)/Cu]N, with the Cu layers always being 200 Å. The series resistor model predicts that in the CPP mode, MR(H) is independent of the ordering of the layers. Nevertheless, the MR(H) curves measured were found to be completely different for the two cases. We suggest that the reason for this difference is that the electron mean free path is long enough that the potential that scatters the electrons is due to pairs of neighboring magnetic layers, which differ for the two types of magnetic multilayers.

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