Fabrication of large uniaxial anisotropy films for anisotropy graded media Yuki Inaba, Robb Morris, Zeenathreddy Tadisina, Zhihong Lu, Vishal V. Warke, Renee Horton, Chris Redden, Iulica Zana, Su Gupta, Bakker Martin, Pieter Visscher, G. B. Thompson and J. W. Harrell MINT Center and Departments of Chemistry, Metallurgical & Materials Engineering, and Physics & Astronomy The University of Alabama This project was funded by NSF-MRSEC grant DMR-0213985. Motivation In Hard Disk Drive (HDD) information stored in the magnetization of several magnetic grains. Making small grains with good thermal stability and writability is very important to realize ultra high density recording. Recently, new concepts such as ECC media[1], Hard/Soft stacked media[2] Exchange spring media[3] and Anisotropy graded media[4] have been reported to reduce the switching field with maintaining good Results and discussion 1. Seed layer effect 3000 2500 2000 1500 1000 ntensity (counts) Ru/Cu/Ta/Si Ru/Ta/Si Ru/Cu/Si Ru/Si 1.0 0.8 0.6 0.4 0.2 0.0 Normalized intensity -10 -5 0 5 10 Omega (deg.) Ru/Cu/Ta/Si Ru/Ta/Si Ru and CoPt with Ta pre-seed layer showed strong hcp (0002) orientation. The peak intensity of specimens without Ta pre-seed layer is much -1000 -500 0 500 1000 1500 M (emu/cm 3 ) Ru/Cu/Ta/Si Ru/Ta/Si Ru/Cu/Si Ru/Si -1000 -500 0 500 1000 1500 M (emu/cm 3 ) Ru/Cu/Ta/Si Ru/Ta/Si Ru/Cu/Si Ru/Si Ru Ot f l I l thermal stability. In these concepts, the grains are composed of magnetically hard and soft parts. For hard part, a very high anisotropy energy, K u ,, of order 10 7 (erg/cm 3 ) is required to make full use of these concepts. In this work, we have focused on fabricating magnetically hard thin films with high K u for anisotropy graded media. We report the results of seed layer optimization through structural analysis, and magnetic layer thickness dependence of structural and magnetic properties 500 0 In 45 44 43 42 41 40 2theta (deg.) smaller than those with Ta layer. Fig. 2 XRD θ-2θ profile of specimens with Ru/Cu/Ta, Ru/Ta, Ru/Cu, Ru seedlayers. Inset figure shows Ru rocking curve results of specimens with Ta pre-seed layer. -1500 -20 -10 0 10 20 H (kOe) -1500 -20 -10 0 10 20 H (kOe) Easy axis of specimens with Ta pre-seed layer is normal to the film plane. Ta pre-seed layer is important to make perpendicular film. Fig. 3 Out of plane and in-plane hysteresis loops for specimens with various kinds of seed layer structure. Out of plane In-plane 1500 2. Magnetic layer thickness dependence 4000 1.0 0.8 ensity 5 nm 10 nm 20 nm 50 nm Ru Out of plane properties. Sample preparation References [1] R. H. Victora and X. Shen, IEEE Trans. Magn., 41, 537 (2005) [2] Y. Inaba, et. al, J. Magn. Soc. Jpn., 29, 239 (2005) [3] D. Suess, et. al, Appl. Phys. Lett., 87, 012504 (2005) [4] D. Suess, Appl. Phys. Lett., 89, 113105 (2006) -1500 -1000 -500 0 500 1000 M (emu/cm 3 ) -15 -10 -5 0 5 10 15 H (kOe) 5 nm 10 nm 20 nm 50 nm 3000 2000 1000 0 Intensity (counts) 45 44 43 42 41 40 2theta (deg.) 5 nm 10 nm 20 nm 50 nm 0.6 0.4 0.2 0.0 Normalized inte -10 -5 0 5 10 Omega (deg.) Fig. 4 XRD θ-2θ profile of specimens with different CoPt thicknesses with Ru/Cu/Ta seedlayers. Inset figure shows Ru rocking curve results. -1500 -1000 -500 0 500 1000 1500 M (emu/cm 3 ) -15 -10 -5 0 5 10 15 H (kOe) 5 nm 10 nm 20 nm 50 nm Fig. 5 Integral intensities calculated from θ-2θ scan. In-plane With Ta pre-seed layer Without Ta pre-seed layer Deposition Deposition DC magnetron sputtering Film structure Film structure Sputtering system Sputtering system Co 80 Pt 20 (δ nm)/Seed layer/Si sub AJA system, Shamrock Substrate Substrate (No substrate heating during deposition) 2” Si substrate (thickness : 300 μm) (δ = 5 ~ 50 nm) Thick film shows bow-tie shape in out of plane measurement, indicating there is a strong exchange coupling between grains. Squareness increases as film thickness decreases. Intensity of CoPt decreased as thickness decreased. Integrated intensity of CoPt is proportional to magnetic layer thickness. hcp structure of CoPt is formed in the initial atomic layers. Fig. 6 Out of plane and in-plane hysteresis loops for specimens with various CoPt thicknesses. Seed layer was Ru/Cu/Ta. Fig. 7 Change of K u as functions of magnetic layer thickness. M s of 5 nm film showed small value resulting in the small calculated value of K u . Film may be damaged during cutting process with dicing saw. Future plans Si CoPt Pt cap Film thickness : 50 nm Graded from 30 – 0 at. % 100 80 60 40 tent (at. %) Pt content Co content Conclusion • Ta pre-seed layer is important for CoPt (0002)/Ru (0002) layer to make easy axis normal to the film plane. • Large K u of order 10 7 was obtained with Ta pre-seed layers. • Squareness of CoPt film increased as film thickness decreased. • M s of 5 nm film showed small value resulting in the small calculated l f K Co 80 Pt 20 20 nm (hcp) Ru 50 nm (hcp) Cu 10 nm (fcc) Ta 5 nm (Amorphous ) Co 80 Pt 20 20 nm (hcp) Ru 50 nm (hcp) Cu 10 nm (fcc) Co 80 Pt 20 20 nm (hcp) Ru 50 nm (hcp) Ta 5 nm (Amorphous) Co 80 Pt 20 20 nm (hcp) Ru 50 nm (hcp) Magnetic layer Seed layer Pre-seed layer 1. Continuous anisotropy graded media 2. Discrete anisotropy graded media Co 80 Pt 20 Co 85 Pt 15 Co 90 Pt 10 Co 95 Pt 5 [Co(0.6nm)/Pt(0.4nm)] n (Co 80 Pt 20 )+3rd additive (Co 80 Pt 20 )+3rd additive (Co 80 Pt 20 )+3rd additive (Co 80 Pt 20 )+3rd additive Center For Materials For Information Technology An NSF Materials Research Science and Engineering Center The University of Alabama 40 20 0 Cont 50 40 30 20 10 0 Position (nm) value of K u . Si substrate Si substrate Si substrate Si substrate Fig. 1 Film structure for seed layer structure optimization. (CoPt layer was deposited with alloy target) [Co(0.6nm)/Pt(0.8nm)] n [Co(0.6nm)/Pt(1.2nm)] n [Co(0.6nm)/Pt(1.6nm)] n