Journal of Magnetism and Magnetic Materials 317, 53 (2007)

R. Salzer, D. Spemann, P. Esquinazi, R. Höhne, A. Setzer, K. Schindler, H. Schmidt and T. Butz

Abstract
We have studied the field and temperature dependence of the magnetic moment of single crystalline sapphire substrates with different surface orientations. All the substrates show a ferromagnetic behavior that partially changes after surface cleaning. The amount of magnetic impurities in the substrates was determined by particle induced X-ray emission. The overall analysis of the data indicates that the magnetic impurities very likely contribute to the measured ferromagnetic behavior but does not rule out completely intrinsic contributions. Our work stresses the necessity to use other than bulk characterization methods for the study of weak ferromagnetic signals of thin films grown on oxide substrates.