Probing Graded Perpendicular Anisotropy with Polarized Neutron Reflectometry


Probing Graded Perpendicular Anisotropy with Polarized Neutron Reflectometry

Greene, P.; Gilbert, D.; Kirby, B.; Borchers, J.; Lau, J.; Shull, R.; Chih-Huang, L.; Osten, J.; Fassbender, J.; Davies, J.; Fitzsimmons, M.; Zimanyi, G.; Liu, K.

Magnetic nanostructures with graded anisotropy offer a solution to both thermal stability and writability challenges in advanced magnetic recording media. The interlayer exchange coupling lowers the overall coercivity, facilitating the writing process, while the magnetically hard layer provides pinning for the media and ensures its thermal stability. However, it is challenging to probe and tune the depth-dependent anisotropy gradient, as conventional magnetometry approaches only give convoluted response from the entire layer. In this work, we have investigated magnetization reversal in Co/Pd and Co/Pt films and patterned structures with perpendicular anisotropy using polarized neutron reflectometry (PNR), along with magnetometry and structural characterizations. Perpendicular magnetic anisotropy is varied by changing the growth conditions during synthesis (Co layer thickness, sputtering pressure, or multilayer deposition order), or post-deposition ion irradiation. PNR directly reveals depth-dependent magnetization profiles along the in-plane magnetic hard axis, which reflect the magnetic anisotropy gradient as different amounts of magnetic moment come into alignment with the in-plane field. Effects of lateral patterning have also been investigated in patterned nanostructures (networks and nanodots). An increase in coercivity and a modified switching field distribution are observed in patterned structures. This is due to the reduced lateral dimensions which limit the domain nucleation and propagation commonly found in unpatterned films. These results demonstrate attractive features of nanostructures with graded anisotropy towards future magnetic recording applications.
Work supported by the US NSF (DMR-1008791 & ECCS-0925626).

Related publications

  • Invited lecture (Conferences)
    ACNS American Conference on Neutron Scattering, 24.-28.06.2012, Washington, DC, USA

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Publ.-Id: 17253