Microstructure and magnetic anisotropy of ultrathin Co/Pt multilayers grown on GaAs (1̄1̄1̄) by molecular-beam epitaxy

Abstract

Multilayers of (Co3 Å, Pt15 Å)x, x=15 or 30 repeats, with or without a 200 Å silver buffer layer, were grown on GaAs (111) substrates by molecular-beam epitaxy. Vibrating sample magnetometry measurements confirmed that the samples with the Ag buffer layer show strong uniaxial magnetic anisotropy perpendicular to the surface. The perpendicular anisotropy exhibited by these metallic superlattices is discussed in terms of the microstructure of the overall multilayer stack, as well as the structural characteristics of the Co interface layer. Samples grown on the Ag buffer layer show strong (111) texture with 30–40-nm-size twin-related grains. These grains, correspond to the two possible (111) stacking sequence for an fcc lattice, i.e., double positioning. However, direct growth on GaAs (111) results in randomly oriented 10–20 nm grains. All samples exhibit a repeat period of 1.83 nm in both low-angle reflectivity and high-angle Θ–2Θ x-ray scattering measurements. In addition, transverse scans through the low-angle multilayer Bragg peaks show the interfaces to be diffuse in nature indicative of considerable in-plane inhomogeneity and/or compound formation. High-resolution electron microscopy measurements of cross sections compared with image simulations confirm that the interface layer is diffuse and its stoichiometry is such that the Co occupation is less than 40%. Redistribution of Co should then extend over at least four monolayers. The nanostructure of the samples grown with the Ag buffer layer comprises an eight atomic layer repeat with the Co interface layer diffuse over four monolayers. The microstructure is strongly (111) textured with columns of twin related 30-nm-sized grains. It is suggested that the combination of interdiffusion, highly oriented but twin-related columnar growth, small grain size with a possible nanometer-scale second phase may be the key to the understanding of the perpendicular anisotropy observed in these (111) superlattices.

PERPENDICULAR MAGNETIC ANISOTROPY AND MAGNETO-OPTICAL KEER PROPERTIES OF Co/(Pd-Au) METALLIC MULTILAYERS

“…The increase of Kv with addition of Au can be explained to be due to strain contribution to Kv' Although other factors. such as the atomic mixing or compound formation [13], or the polarization of the Pd layers at the interface[5j may contribute to the perpendicular anisotropy, magnetoelastic effects due to the in~ plane strain are quite important in understanding the perpendicular anisotropy of magnetic multilayers.…”

Magnetic anisotropy and magneto-optical Kerr effect of metallic multilayers

“…The increase in K ν on addition of Au can be explained to be due to the strain contribution to K ν . Although other factors such as the atomic mixing or compound formation [12] or the polarization of the Pd layers at the interface [5] may contribute to the perpendicular anisotropy magnetoelastic effects due to the in-plane strain are quite important in understanding the perpendicular anisotropy of magnetic multilayers.…”

Interface and Volume Anisotropy of MBE-Grown Co/Pt (111), (110) and (001) and Sputtered CO/Pt Multilayers

“…Chien et al [9] suggested that perpendicularly aligned Co-Co pairs at stacking faults in a partially chemically ordered CoPt 3 phase at the interfaces might explain the orientation dependence including the strong uniaxial in-plane anisotropy for [1l0]-oriented multilayers. However, the density of stacking faults necessary to produce a considerable number of Co-Co pairs could not be confirmed [10,11]. Nevertheless, short-range chemical ordering was detected in [11l]-oriented multilayers [12] using synchrotron X-ray diffraction.…”