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The key component of a hard disk medium is a Co-based magnetic layer (ML) grown on a Ru seed layer. The ML nanostructure, composed of less than 10 nm grains, is believed to be controlled by this seed layer. We successfully used scanning transmission electron microscopy energy dispersive spectrometry simultaneous composition-based imaging and Moiré pattern analysis for determining the mutual structural and orientation relationship between the two layers revealing a grain-to-grain agreement. The method presented here can be utilized for observing structural correlations between consecutive polycrystalline thin film layers in general.

In perpendicular hard disk memory media, nanometric magnetic Co-rich grains are separated by a ∼1 nm thick nonmagnetic and preferably amorphous intergranular phase (IP). Attempts at observing the IP structure at high resolution using TEM have been obstructed by the superposition of lattice fringes from the crystalline grains extending into the IP region in images. Here we present the first images of a magnetic recording medium produced using a spherical aberration-corrected TEM showing the true amorphous IP structure in contrast to the crystalline grains, allowing the accurate determination of the grain-IP interface and the grain and IP dimensions. It is shown that these aberration-corrected TEM images are functionally superior for analyzing certain features of the ultrahigh capacity data recording media.

In the production of perpendicular magnetic recording (PMR) media, obtaining a desirable nanostructure in the magnetic layer (ML), the topmost layer in a hard disk layer stack (Figure 1), is of critical importance to the performance of the device [1]. ML is a continuous polycrystalline thin film of magnetic grains separated by, ideally, non-magnetic grain boundaries [2]. For example, in a Co-based PMR medium, the element Co is abundant within the grains of ML. Currently, media with average grain diameters less than 10 nm with grain size distributions of ~1 nm standard deviations are manufactured [3]. Different under-layers and seed layers are employed to obtain such grain structures. Figure 1 shows schematically the layer stacks in a typical device, in which ML is deposited on a ruthenium layer. The Ru layer, like ML, exhibits an HCP crystal structure and as a seed layer its nanostructure controls that of the ML. Understanding the structural correlation between these two thin films is important. Owing to the small spatial scales of the features involved in both of these structures, the transmission electron microscope (TEM) is the suitable tool for this investigation. Here, we report the results of our simultaneous observations on the nanostructures of ML and Ru layer using a scanning TEM (STEM)-EDS system. Samples of PMR media based on a CoPtTiO alloy composition were deposited at Western Digital Media (WD) Corp. Plan-view TEM specimens were prepared using conventional grinding-polishing followed by dimple grinding and ion milling using Ar + ions at 4-5 keV. Electron transparent regions in the specimens ranging between 10-30 nm in thickness were used for TEM studies. For the analysis of the specimens the instrument used was an FEI Tecnai G2 F20 TEM. Figure 2 shows a high resolution TEM image obtained from the ML. This layer exhibits an HCP crystal structure with c-axes of all crystals perpendicular to the disk surface. EDS spectra were obtained from regions of specimens thick enough to contain both the ML and Ru layer. In these experiments specimens were tilted 15˚ to enhance the efficiency of the detections of X-rays emitted from the specimen. Distances between two neighboring pixels in the analysis were ~0.7 nm. Energy windows were selected on the spectra in order to obtain chemical maps for the Co and Ru elements based on their K α peaks. Figures 3 and 4 show the elemental maps obtained from a 21 nm × 13 nm area on a sample.The grain size and shape in the ML and Ru layer agree as evident from the chemical maps for the two elements (compare Figures 3 and 4). This important result reveals information about the growth mechanism of the ML as deposited on the Ru layer by showing how closely related the two structures are. With regard to the relative position of the grains a displacement of 2.5 nm was measured between each Co grain and its corresponding Ru grain underneath. This displacement was attributed to the angle between the normal to the sample and the incident electron beam in the TEM column using a simple...

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