Inverse magnetoresistance in Fe/Si ion beam sputtered sandwiches

A series of Fe/Si sandwiches have been prepared by ion beam sputtering at r oom temperature onto glass substrate with the following nomenclature: Glass /Si-20 nm/Fe-5/6 nm/Fe-5 nm/Ru-2 nm. Magnetization measurements have been p erformed at 300 K and show no evidence of antiferromagnetic exchange coupli ng. However, the magnetoresistance curves recorded at 300 K are very intere sting and show an inverse magnetoresistance for sandwiches with Si spacer l ayer thicknesses between 1.2 and 1.5 nm. The resistance is smaller at zero field than at saturation. This inverse magnetoresistance is due to the supe rparamagnetic interfaces and finds its origin in the difference of the elec tronic nature of the Fe/Si interfaces and Fe/Ru interfaces. Fe1-xSix iron s ilicide at Fe/Si interfaces has a scattering spin asymmetry ratio (alpha = rho(down arrow)/rho(up arrow)) larger than one, whereas, Fe with Ru impurit ies at the Fe/Ru interfaces presents a scattering spin asymmetry ratio smal ler than one. (C) 1999 American Institute of Physics. [S0021-8979(99)19008- X].