Structural study of CoCrPt films by anomalous x-ray scattering and extended x-ray absorption fine structure

Abstract

The correlation of elemental chemistry with the particular long-range order in question cannot be obtained by common conventional characterization techniques. Here we report a study of determining the elemental concentrations of the textured Bragg diffraction peak and the averaged local atomic environment of sputtered CoCrPt films using anomalous x-ray scattering and extended x-ray absorption fine structures. The elemental compositions of the textured peak in these polycrystalline nanostructured films differed from the average global film composition. The higher Cr concentration in the textured peak indicated that a significant amount of Cr did not segregate towards the grain boundaries as a result of the low sputtering temperature and pressure used. The structural observations were consistent with the magnetic results.

Anomalous X-ray Scattering for Determination of Nanostructured Alloy Formation and Site-specific Chemistry of Bragg Peak

“…Since Cr did not preferentially segregate to grain boundaries, a resultant higher magnetic exchange coupling [20] and reduced magnetocrystalline anisotropy constant [21] would reduce the coercivity. Since Pt is known to increase the local disorder and thus coercivity by increasing the magnetocrystalline anisotropy [22], the lower coercivity of 60 nm film [5] suggested that less Pt existed in the CoCrPt (002) Bragg peak, compared with that of 30 nm film. This argument is consistent with the observed higher Cr content (Fig.…”

“…CoCrPt films [5] The magnetic properties of sputtered magnetic Co-Cr based films, as longitudinal and perpendicular recording media materials, are controlled by the alloy composition and the degree of phase separation of Co and Cr, the alignment of the columnar structures, the degree of Cr segregation at the grain boundaries and the mosaic of the texture. It is important to achieve a proper crystallographic texture with optimal composition to control the magnetocrystalline anisotropy.…”

“…The conventional phase diagram may not necessarily be applicable in predicting the miscibility or phase separation of nanostructured materials, since it does not take into consideration of the significant contribution of surface and interfaces in these materials. A study was carried out to determine the elemental concentrations of the textured Bragg peak and the averaged local atomic environment of sputtered CoCrPt films using AXS and EXAFS [5].…”

“…Using anomalous x-ray scattering, it was shown that nanostructured NiCo films did not necessarily form solid solution as expected from their phase diagram or suggested by the results of conventional XRD [4]. The compositions of constituent elements of the textured Bragg peak of CoCrPt film were also investigated using this method [5]. The limitations of using conventional XRD alone for studying nanostructured alloys are discussed.…”

Note: Application of a pixel-array area detector to simultaneous single crystal x-ray diffraction and x-ray absorption spectroscopy measurements

“…Thus, the momentum transfer along the specular direction is measured. It is a different measurement technique as compared to anomalous XRD (diffraction at a fixed momentum transfer), 16 diffraction anomalous fine structure (DAFS, absorption at a fixed momentum transfer), 17 and crystal truncation rod (CTR, surface sensitive). 18 Figure 3(b) shows the XANES result collected simultaneously with the XRD measurement.…”