Contactless magnetoresistance studies of Co∕Cu multilayers using the infrared magnetorefractive effect

The magnetotransport properties of giant magnetoresistive Co∕Cu multilayers are studied with the magnetorefractive effect: a noncontact technique, which uses infrared electromagnetic radiation. Four Co∕Cu samples were analyzed with the structure (Co_15.5 Å∕Cu_x)₂₅ which exhibit magnetoresistance values from 1.9 to 65 %. The magnetorefractive curves were modeled using the complex dielectric function as derived by Jacquet and Valet [J. C. Jacquet and T. Valet, Magnetic Ultrathin Films, Multilayer and Surfaces, edited by E. Marinero (Materials Research Society, Pittsburgh, 1995)]. The shape and magnitude of the curves were found to be very sensitive to the interface scattering lifetime. This classical model is successful in simulating the long wavelength behavior, but is not able to reproduce the correct shape or sign at short wavelengths where the band structure of the materials becomes important. The good agreement at long wavelengths between electrical magnetotransport measurements and the noncontact magnetorefractive effect demonstrates the possibilities of using infrared reflection spectroscopy for the characterization of giant magnetoresistive systems.