Spatially resolving variations in giant magnetoresistance, undetectable with four-point probe measurements, using infrared microspectroscopy

Magnetorefractive infrared (IR) microspectroscopy is demonstrated to resolve spatial variations in giant magnetoresistance (GMR) and, by modelling, provide an insight into the origin of the variations. Spatial variations are shown to be masked in conventional four-point probe electrical or IR spectral measurements. IR microspectroscopy was performed at the SMIS beamline at the SOLEIL synchrotron, modified to enable measurements in magnetic fields. A GMR gradient was induced in a CoFe/Cu multilayer sample by annealing in a temperature gradient. Modelling revealed that variations in GMR at 900 Oe could be attributed to local variations in interlayer coupling locally changing the switching field.