Magneto-optical study of magnetic multilayer system

Magneto-optical properties of magnetic materials can be investigated effectively by the use of Magneto-optical Kerr Effect (MOKE). A magnetic multilayer system in the structure of CoO(30 Å)/Cu(tCu,)/ NiFe(30 Å) (tCu = 0, 3, 6,. . . , 21 Å) has been systematically studied by Polar and Longitudinal MOKE techniques. In Polar Configuration, we have observed the hysteresis loops with large peak-to-peak amplitude. The exchange field HE and the coercivity HC were observed to be zero in this configuration. The polar Kerr rotation is determined and showed to be proportional to the magnetic field applied. In Longitudinal Configuration, we have determined the hysteresis loops that the exchange field and coercivity were non-zero. Also the exchange field and coercivity found in CoO/NiFe bilayer were larger than that have been observed. The Kerr intensities in Longitudinal Configuration are about 10 times smaller than that in Polar Configuration. As the thicknesses of CoO layer in our samples are 30 Å, the Neel temperature TN of CoO is much lower than that of bulk CoO. Due to the limitation of our sample cooling system, the finite size effect resulted in the fact that the hysteresis loops were only measured above the Neel temperature. Thus, we could not observe the shifted hysteresis loops in both configurations as the Cu spacer layer thickness and the temperature varied. Also there was no hysteresis loop to be observed for CoO(30 Å) monolayer thin film. A possible way to improve the existing cooling system is suggested. Finally, by Longitudinal MOKE technique we distinguished a special sample Co/Cu/NiFe which demonstrated a two-step hysteresis loop due to the superposition of the top and bottom ferromagnetic layers