Magnetization Reversal in Nanostructures with Graded Perpendicular Anisotropy


Magnetization Reversal in Nanostructures with Graded Perpendicular Anisotropy

Greene, P. K.; Gilbert, D. A.; Kirby, B. J.; Borchers, J. A.; Lau, J. W.; Lai, C.-H.; Osten, J.; Fassbender, J.; Davies, J. E.; Fitzsimmons, M. R.; 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. Magnetization reversal in such materials can be influenced by both the magnetic anisotropy gradient along the film depth and the lateral feature size. We have explored magnetization reversal in Co/Pd films and patterned structures. Perpendicular magnetic anisotropy is varied by changing the Co thicknesses or sputtering pressure during growth. Effects of deposition order and ion irradiation have been studied by x-ray diffraction, transmission electron microscopy, magnetometry, and first-order reversal curves. Structural integrity and amount of disorders are found to sensitively influence the magnetic properties. Reversal in highly ordered films is dominated by nucleation, propagation, and annihilation of domain walls while in disordered films magnetization reversal is largely by domain wall pinning and magnetization rotation. Depth-dependent magnetization profiles and magnetic anisotropy have been confirmed by polarized neutron reflectivity. Effects of lateral patterning have been investigated in patterned nanodots (down to 60nm diameter). 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).

Keywords: Magnetic nanostructures

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  • Invited lecture (Conferences)
    NordicSpin'12 - Third Nordic Workshop on Spintronics and Nanomagnetism, 22.-25.04.2012, Varberg, Schweden

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