Infrared reflectance and magnetorefractive effects in metal–insulator CoFe–Al2O3 granular films

The infrared reflectance of (Co50Fe50)x–(Al2O3)1−x granular films which exhibit tunneling magnetoresistance has been measured in the wavelength range 2–25 μm for compositions both above and below the critical percolation volume fraction. The modifications of the Al2O3 Restrahlen reflection region are well accounted for in an effective medium model. In addition, frequency dependent changes of the reflection have been observed under the application of magnetic fields up to 12 kOe. At the longitudinal optic reflection edge around 9 μm distinctive magnetic signatures are found below and above the percolation threshold φc at x=0.17.