On the Physics of Magnetic Anisotropy in Co/Pd Multilayer Thin Films
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0998-J05-04
On the Physics of Magnetic Anisotropy in Co/Pd Multilayer Thin Films Darren Smith1, Shishan Zhang2, Wolfgang Donner3, Chunsheng E1, T Randall Lee4, Sahkrat Khizroev5, and Dmitri Litvinov1 1 Electrical and Computer Engineering, University of Houston, Houston, TX, 77004 2 Chemical and Biomolecular Engineering, University of Houston, Houston, TX, 77004 3 Physics, University of Houston, Houston, TX, 77004 4 Chemistry, University of Houston, Houston, TX, 77004 5 Electrical Engineering, University of California - Riverside, Riverside, CA, 92521 ABSTRACT (Co/Pd)N multilayers with Co and Pd layer thicknesses of only a few monolayers exhibit high vertical magnetic anisotropy and have been extensively explored as recording medium candidates for high density magnetic recording applications. In the work reported here, the magnetic properties of (Co/Pd)N multilayers deposited by magnetron sputtering and designed for bit-patterned medium applications are correlated with X-Ray Photoelectron Spectroscopy (XPS) data -- an approach commonly used to probe the binding energies and valence band positions. Although the XPS probing depth is limited to ~2-3 nm, it is sufficient for the evaluation of the 12 topmost bilayers in a multilayer stack, and allows us to infer the relevant details of the bandstructure of the entire film. Confirming theoretical predictions, we demonstrate that the degree of d-shell hybridization at Co/Pd interfaces directly correlates with the magnitude of the magnetic anisotropy. Significantly, the highest hybridization of Pd atoms is observed for about one monolayer thick Co layers in the bilayer stack. Variation of the deposition conditions (e.g., deposition pressure) shows a measurable influence on d-electron hybridization, multilayer microstructure, and magnetic anisotropy. INTRODUCTION (Co/Pd)N multilayer films in which the cobalt and palladium layers are only a few monolayers thick exhibit high magnetic anisotropy perpendicular to the film surface, where variations of Co and Pd layer thicknesses in a bilayer stack exert a strong effect on the magnetic properties of the multilayer.1 Such magnetic multilayers have been extensively explored as recording medium candidates for high density magnetic recording applications.2-4 The perpendicular anisotropy is believed to arise from the hybridization of the d-shell electrons at the interfaces between the Co and Pd layers.5,6 EXPERIMENT High anisotropy exchange-coupled (Co/Pd)N multilayers designed for bit-patterned medium applications were deposited using room temperature magnetron sputtering onto oxidized silicon substrates with a 5 nm Ta layer to diminish grain size and promote exchange coupling in the films7. The thicknesses of the Co and Pd layers and the deposition pressures were systematically varied to modify the magnetic properties of the films. The multilayers were patterned into large arrays of 200 nm islands using ion-beam proximity lithography, which has
been described elsewhere8. The magnetic properties of continuous and patterned multilaye
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