Magnetic properties of Co/Pt-multilayers

The magnetic properties of (111)-textured Co/Pt-multilayers have been studied theoretically by means of spin-polarized LMTO-band-structure calculations. In contrast to the interpretation of earlier experimental investigations, the Pt-layers have been found to be significantly magnetized by the adjacent Co-layers. This finding ensures that the Co-layers are exchange-coupled even for relatively thick Pt-interlayers. To get some information on the consequences of interface mixing we have used the ASA-version of the spin-polarized relativistic KKR-method of band-structure calculation to investigate the electronic and magnetic properties of Pt-(Co)-impurities in the various layers of the Co/Pt-multilayers. Our non-self-consistent results indicate that for most cases a slight increase in the magnetic moments has to be expected. To study experimentally the magnetic properties of the Pt-layers of vapor-deposited samples we have made use of the magnetic dichroism in X-ray absorption. This new technique allows to probe the Pt-layers separately and to estimate the average moment of this subsystem. While the estimated moments are in all cases somewhat higher than our corresponding theoretical results, their dependence on the Pt-layer thickness is in very satisfying agreement with the theoretical predictions

Spin-dependent x-ray absorption in Co/Pt multilayers and Co50Pt50Co_{50}Pt_{50} alloy

The spin dependence of $L_{2,3}$ absorption in 5d atoms oriented in a ferromagnetic matrix contains information on the spin density of the empty d‐projected states of the absorbing atom. Spin‐dependent absorption spectroscopy using circularly polarized synchrotron radiation was applied to study the polarization of the Pt atoms in the binary alloy $Co_{50}Pt_{50}$ and Pt/Co layered structures, which are promising candidates for magneto‐optical recording. The spin‐dependent absorption signals for vapor‐deposited 250(4 Å Co+18 Å Pt) and 250(6 Å Co+18 Å Pt) multilayers indicate a ferromagnetic coupling on Pt and Co atoms with a significant Pt polarization. This is reduced on average by about 60% with respect to the Pt polarization in the $Co_{50}Pt_{50}$ alloy. The experimental results are discussed on the basis of spin‐polarized band‐structure calculations

Distribution of magnetic moments in Co/Pt and Co/Pt/Ir/Pt multilayers detected by magnetic x-ray absorption

Measurements of the spin-dependent absorption have been performed at the L2,3 edges in Pt and Ir in the multilayered structures 4ÅCo+χÅPt (χ = 9, 16, 23, 30, 40) and 4ÅCo+11ÅPt+8ÅIr+11ÅPt. The samples were prepared by sputtering and evaporating, respectively, and show a large perpendicular anisotropy. The measured circular magnetic X-ray dichroism (CMXD) profiles indicate a significant spin polarization of the Pt and the Ir interlayer. The results show that the moments of the Pt interlayers as well as of the innermost Ir layers couple ferromagnetically to the Co layers. The experimental findings are compared with the magnetic moment distribution for sharp interfaces obtained from linear muffin tin orbital (LMTO) band structure calculations

Sputtering pressure effect on microstructure of surface and interface, and on coercivity of Co/Pt multilayers

Thin Co/Pt multilayers were prepared on Si and glass substrates by sputtering with Ar pressures ranging from 2.5 to 15 mTorr. The bilayer structure of the samples was Co(3 Å)/Pt(15 Å)×17, and all samples had the easy axis of magnetization perpendicular to the sample surface as determined with a SQUID magnetometer. All samples retained the layered structure, as revealed by low-angle x-ray diffraction. In addition, diffraction peaks due to the formation of Co-Pt compounds (presumably at the interfaces between Co and Pt) were identified. The coercivity of samples changed from about 400 Oe for films deposited at low Ar sputtering pressure (2.5 mTorr) to as high as 2300 Oe for films deposited at high Ar pressure (15 mTorr). Ellipsometry and atomic force microscopy were used to study surface roughness and microstructure of samples prepared at different sputtering pressures