Spin and orbital moment in amorphous ${\text{Co}}_{68}{\text{Fe}}_{24}{\text{Zr}}_8$ layers

The ratio of the orbital to the spin magnetic moment was determined for both Fe and Co in amorphous ${\text{Co}}_{68}{\text{Fe}}_{24}{\text{Zr}}_8$ layers using x-ray circular dichroism. The investigations were performed on both thick ${\text{Co}}_{68}{\text{Fe}}_{24}{\text{Zr}}_8$ layers as well as on amorphous ${\text{Co}}_{68}{\text{Fe}}_{24}{\text{Zr}}_8/{\text{Al}}_{70}{\text{Zr}}_{30}$ multilayers grown by dc sputtering. Structural characterization was performed using x-ray reflectometry, x-ray diffraction, and transmission electron microscopy. X-ray circular dichroism, x-ray magnetic scattering as well as the magneto-optic Kerr effect were used to characterize the magnetic properties of the amorphous materials. The ratio of the orbital to spin moments in the single CoFeZr-layer sample was $0.012\pm 0.005$ for Fe and $0.078\pm 0.005$ for Co. Substantial reduction in the the ratio of the orbital to spin moments was observed with decreasing CoFeZr-layer thickness.

Figure 1

(Color online) Specular reflectivity (upper curve) and longitudinal diffuse scan (lower curve) for the single $200\text{Å}$ CoFeZr layer. The specular data (circles) are well fitted (line) for all scattering vectors. The fringes observed in the specular data are replicated in the longitudinal diffuse data recorded with a sample offset of $-0.1°$, clearly illustrating that vertical correlations exist in the topological roughness that extend over the entire sample thickness.

Figure 2

(Color online) Transverse diffuse, or rocking curve, for the $200\text{Å}$ single-layer CoFeZr sample. The data were recorded at a fixed out-of-plane scattering vector of $q_z=0.222{\text{Å}}^{-1}$. The specular ridge at $q_x=0$ is broadened as a result of roughness on a large lateral length scale. From the ratio of the specular and diffuse scatter a lower limit for the amplitude of the topological roughness is $1.0\pm 0.2\text{Å}$.

Figure 3

(Color online) Specular reflectivity for the multilayer samples. Sequential curves have been offset by decades of intensity for clarity. The multilayer peak positions correspond to fitted bilayer thicknesses of $39.3\pm 0.1\text{Å}$, $47.9\pm 0.1\text{Å}$, and $57.3\pm 0.5\text{Å}$ for samples 10/30, 20/30, and 30/30, respectively. The solid lines are simulated fits to the data (circles).

Figure 4

(Color online) Full reciprocal space map of the diffuse scattering data from sample 20/30. Data is presented on a logarithmic scale. The diffuse scattering is predominantly found in streaks at the out-of-plane scattering vectors of the multilayer peaks seen in the specular scans shown in Fig. 3. The slight curvature of the Bragg sheets at high $q_x$ is caused by refraction effects when either the incident or exit beams are at the critical angle.

Figure 5

High-resolution TEM images of the CoFeZr/AlZr multilayer samples in cross-sectional view. The sample with the thinnest CoFeZr-layer thickness, 10/30 is shown in (a). An amorphous structure is observed throughout the deposited material, except for the Al cap layer at the top. In (b) the sample with the thickest CoFeZr layer, 30/30, is shown. The white arrow indicates a region where the interface morphology is changed which then propagates throughout the remainder of the multilayers. The silicon substrate is seen at the bottom of each image.

Figure 6

Selected area electron-diffraction pattern in the TEM from the $10\text{Å}$ CoFeZr multilayer sample in top-view geometry, acquired including a part of the silicon substrate (spot pattern). Broad dark bands indicates an amorphous structure of the CoFeZr and AlZr layers. The sharp ring at approximately $1.44\text{Å}$ correspond to polycrystalline Al 220 planes, originating from the cap layer (see Fig. 5). White arrows indicate the expected spacing of (111), (200), (220), and (113) reflections in Al. The brightness of the left-hand and right-hand parts of the image is different for enhancing the dynamic range in the figure and the intensity scale was inverted for clarity.

Figure 7

Room-temperature magnetization as a function of applied field recorded using the magneto-optical Kerr rotation effect.

Figure 8

(Color online) The difference in the reflected signal as a function of applied field for the single-layer sample. The Fe (circles and line) and Co (line) loops are similar within experimental error and show a coercive field of $1.7\pm 0.1\text{mT}$.

Figure 9

(Color online) Electron yield as a function of energy across the Fe (circles and line) and Co (line) $L_3$ and $L_2$ edges for the single $200\text{Å}$ CoFeZr film. The absorption data is an average of two curves collected under opposite but saturating fields and has been normalized to give a step height of unity across the two edges.

Figure 10

(Color online) The difference in electron yield as a function of energy across the Fe and Co edges (circles and line) and the cumulative integral of the difference signal (line) for the single CoFeZr film. The data was recorded simultaneously with the absorption signals shown in Fig. 9. Artifacts associated with recording the electron yield in a field have been removed by averaging two curves collected under opposite but saturating fields. No normalization or correction terms have been applied to the data.

Figure 11

(Color online) The difference in electron yield as a function of energy across the Fe and Co edges (circles and line) and the cumulative integral of the difference signal (line) for the 30/30 multilayered sample. The data treatment is identical to that applied to the data in Fig. 10. The lower signal to noise arises from the thickness of the effective capping layer which is the sum of the protective alumina layer and the top AlZr layer of the bilayer.