SPring-8, the large synchrotron radiation facility

Industrial Application

Grazing incidence X-ray fluorescence of a spin-valve multilayers

A giant magnetoresistance (GMR) head is one of the key components for high density magnetic recording which composed of nanometer thick magnetic and nonmagnetic layers with a spin-valve structure. To improve their performances, evaluation of film thickness, its density, interfacial roughness, or the existence of mixing layer are important. However, the spin-valve part consisted of CoFeB, Cu and NiFe are usually hard to distinguish since their atomic number, the density, and the crystal structure are almost the same.
To solve the difficulty, a grazing incidence X-ray fluorescence with wavelength dispersive detector (WD-GIXF) has been developed at industrial beamline BL16XU. The angular dependence of an element specific fluorescence intensity measured by the WD detector provides their depth profiles.
The WD-GIXF and the X-ray reflectivity measurement have been done for a spin-valve sample of Ta(6)/PdPtMn(25)/CoFeB(2)/Cu(3)/CoFeB(2)/NiFe(4)/Ta(5)/Si-sub. A number in parenthesis is the designed thickness in nm.
Results of a grazing angle scan are shown in Fig.1. In the figure, the fluorescence intensity from the element in each layer are shown along with the momentum transfer. The fluorescence intensity show a clear oscillation structure that originated from the interference of X-ray inside the layers. The solid line shows the calculation from the layered model.
In the analysis, we developed the optimization program that calculates the fluorescence yield from the energy flow of X-ray in the sample. The fluorescence from each element and the reflectivity profiles have been simultaneously optimized to the layered model. The calculated layer profile is shown in Fig. 2. We have succeeded to separate the spin valve layers and to evaluate the increase of interfacial roughness in the thermally annealed sample.

provided by Naoki Awaji, Fujitsu Laboratories LTD

Fig. 1. Examples of Grazing angle dependence of fluorescence yields for the element corresponding to each layer. The solid line represents the calculation based on the layerd model.

Fig. 2. Layer profile of the sample reconstructed from the results of GIXF analysis, where T.L. is the transition layer and D.L. is the dead layer introduced to reproduce the measured data. Numbers with arrow indicate the interfacial roughness.