Investigation of magnetic-nonmagnetic multilayers by ellipsometric and magneto-optic methods
Magnetic multilayers have found a wide-ranging use in the field of spintronics as well as in nanoelectronics. In these applications, a precise control of layer thickness and good interface quality in terms of sharpness and smoothness, plays an important role in determination of final device quality. In the case of magnetic multilayers, spectroscopic ellipsometry and magneto-optical investigations could be used simultaneously for characterization during the film growth or after film deposition which is equally important. In the case of magnetic films, it is of interest to employ both optical and magnetic methods as an additional tool for magnetic and structural characterization.
In the present work, spectral ellipsometry and magneto-optical Kerr magnetometery are used for the investigation of Al/NiFe, Cr/Ge/NiFe, and Al/Ge/NiFe multilayers on sital substrate for different thicknesses of topmost layer. When increasing the thickness of topmost layer from 2 nm to 20 nm magnetization curve may show significant changes which could be related with spatial distribution of magnetic moments (see Fig.1). It shows the dependence of coerecivity on thickness of topmost layer. Ellipsometric parameters also demonstrate the dependence of refractive indexes of individual layers on thickness as shown in Fig. 2. The ellipsometry method is indirect and requires fitting the modeling and experimental data. This was done with the use of a generalized characteristic matrix (Abele’s matrices). For Al(Cr)/NiFe we got a good approximation between the experimental and theoretical results but for more complex structure as Cr/Ge/NiFe and Al/Ge/NiFe, there was a larger discrepancy between the model and experimental data suggesting the existence of a more complicated structures, probably with additional gradient layers. We can conclude that the spectroscopic ellipsometery and magneto-optic methods are very efficient to calculate effect of nonmagnetic layers on magnetization curve and also magneto-optic constant for individual layer in multilayer structure.
"Figure 1 -Magnetization curves of Cr/NiFe/sital films for different thicknesses of Cr layer "
"Figure 2- Spectra of ψ for Al/NiFe /Sital for different thickness of Al layers. Solid lines designate the measured spectra and dashed line designate the modelling spectra. "