Effect of Co replacement with Cu on structure and magnetic properties of metastable L11 CoPt thin films
Date Issued
2010
Date
2010
Author(s)
Tan, Chih-Shan
Abstract
Due to increasing recording density toward 1 Tbit/inch2, currently-used perpendicular magnetic media encounter a physical limitation arising from superparamagnetism due to the reduction of grain size to several nanometers. Replacing the recording material with high magnetocrystalline anisotropy (Ku) materials becomes an imminent issue. L11-CoPt, a recently discovered metastable phase of CoPt having a rhombohedral lattice and consisting of alternatively stacked Co and Pt closed-packed atomic planes along [111], exhibits great potential owing to its high Ku of about 3.7 × 107 erg/cm3 and low formation temperature of 200℃. In this study, we replace some Co atoms in L11-CoPt with Cu to modify the microstructure and magnetic properties because L11 phase is thermodynamically stable in CuPt.
(Co1-xCux)50Pt50 thin films with thickness of 20 nm and 50 nm were prepared using magnetron co-sputtering with background vacuum better than 10-8 torr on MgO(111) substrates with 0 ≦ x ≦ 1. Our results show a significant enhancement in out-of-plane coercivity (Hc⊥) from 0.1 to 1.9 kOe for 20-nm-thick films and 0.2 to 2.2 kOe for 50-nm-thick films with x = 23, respectively. This increase accompanies a reduction of in-plane coercivity (Hc//) from 0.5 to 0.02 kOe and from 1.4 to 0.07 kOe for films with thicknesses of 20 and 50 nm respectively. Reduced magnetic domain size from about 500 nm to 100 nm suggests that the enhanced Hc⊥ results from domain wall pinning mechanism. TEM microstructure analysis confirms a nanometer-scaled compositional segregation, forming Co-Pt rich and Cu-Pt rich regions. The nonmagnetic Cu-Pt precipitates may act as pinning sites to confine the domain size and block the domain wall motion.
The results demonstrate that replacing Co by Cu effectively increases the perpendicular magnetic properties of L11-CoPt phase, which further support the possibility to use L11-CoPt in the future high-density recording medium.
Subjects
Co
Cu
replacement structure
magnetic properties
L11
Type
thesis
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