Contactless measurement of giant magnetoresistance in CoAg granular films using infrared transmission spectroscopy

A new technique is presented for studying spin dependent transport properties in mesoscopic magnetic structures which exploits the magnetorefractive effect (MRE). A Fourier transform infrared spectrometer was used to measure the MRE of CoAg granular films deposited on thinned Si(001) substrates. Infrared transmission spectra were recorded over a wavelength range from 2.5 to 18.2 mm in an applied magnetic field up to 1.5 kOe. The resulting relative transmission curves have a minimum at approximately 7 mu m which deepens if the applied magnetic field is increased. This behavior can be described by model calculations in the self-averaging limit from which the scattering rates can be extracted when fitted to the experimental spectra. The field dependent behavior of the MRE reproduces the magnetoresistance behavior measured using a conventional four-point probe demonstrating the capability of the MRE to study magnetotransport without making electrical contacts. (C) 1999 American Institute of Physics. [S0021-8979(99)35608-5].