AVS 55th International Symposium & Exhibition
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI+NC-TuA

Paper MI+NC-TuA12
Perpendicular Anisotropy Graded CoPt/CoPtCr Magnetic Pillars Patterned by Nanosphere Lithography

Tuesday, October 21, 2008, 5:20 pm, Room 206

Session: Magnetic Microscopy and Magnetization Dynamics
Presenter: X. Li, The University of Alabama
Authors: X. Li, The University of Alabama
Z.R. Tadisina, The University of Alabama
A.L. Highsmith, The University of Alabama
S. Gupta, The University of Alabama
Y. Inaba, The University of Alabama
J.W. Harrell, The University of Alabama
Correspondent: Click to Email

Patterned magnetic nanostructures such as nanodots and nanopillars are now an extremely active area of research for applications for next generation media,1 as well as novel logic and spintronic memory devices. Bit patterned media is one of the most promising candidates to overcome the tradeoff between thermal stability and recording writability. This work will detail the deposition of perpendicular magnetic anisotropic media, a unique patterning approach using nanosphere lithography, and magnetic characterization of the patterned nanostructures. Process optimization of perpendicular magnetron sputtered CoPt and CoPtCr films of various compositions was carried out using seed layers of Ta and Ru. The anisotropy Ku ranged from 2 × 107 erg/cm3 to 2×106 erg/cm3 as a function of film thickness and Cr concentration. Nanosphere lithography2 was used to pattern the magnetic films into nanopillars with controlled size. A self-assembled nanosphere monolayer was first prepared, tailored to a discrete dot mask by shrinking the spheres using reactive ion etching, and then transferred to hard masks and, finally, the magnetic media, by a combination of ion milling and reactive ion etching. Magnetic nanopillars with diameters ranging from 90 nm to those approaching 10 nm with correspondingly increasing pitch are obtained. The size dependence of the magnetization process, the thermal stability, and switching dynamics of the pillars are characterized in an alternating gradient magnetometer (AGM) and magneto-optic Kerr effect (MOKE) system by using angle-dependent and time-dependent remanent coercivity measurements fitted to Sharrock’s equation over a wide range of timescales. A significant increase of thermal stability and coercivity was demonstrated with the decrease of pillar size. The reversal mechanism is similar to reported results of nucleation of a small reversed volume followed by rapid domain wall motion.3

1 Robert F. Service, Science 314, 1868 (2006).
2 C. L. Haynes and R. P. Van Duyne, J. Phys. Chem. B 105, 5599 (2001).
3 T. Thomson, G. Hu, and B. D. Terris, Phys. Rev. Lett. 96, 257204 (2006).