Ion-driven magnetic nanostructures

Recently it has been demonstrated that ion irradiation of ultrathin magnetic films and multilayer structures is a versatile tool to modify the magnetic properties of these systems in laterally confined areas [1–3]. In most cases the modification of the magnetic anisotropy or the different exchange coupling contributions present in multilayered films are due to a post deposition modification of the interface structure. Depending on the enthalpy of mixing light ion irradiation may result in a roughening or a sharpening of the interface on the atomic level. Due to the local nature of the ion-solid interaction these modifications can be restricted to confined areas resulting in magnetically patterned films without a modification of the surface topography.
An alternative route to ion-driven magnetic nanostructures relies on ion implantation. By doping magnetic thin films in a percentage range with Cr or rare earth transition metals either the Curie temperature [4] or the magnetic damping behavior [5] can be adjusted. In combination with focused ion beam techniques magnetic nanostructures can be written directly into the film structure. Applications in the area of patterned storage media are evaluated currently.
The third approach makes use of ion beam synthesis of magnetic nanoparticles in a nonmagnetic single crystalline oxide host matrix [6]. Magnetic ions are implanted into the host material which leads to a supersaturation of these ions. During implantation at elevated temperatures or a succeeding annealing step the metallic precipitates grow and form, depending on their size and structure, ferromagnetic nanoparticles.
The current status of these different techniques with respect to magnetic nanostructure formation will be reviewed.
References:
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[2] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[3] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett., 86, 162502 (2005).
[4] L. Folks, R. E. Fontana, B. A. Gurney, J. R. Childress, S. Maat, J. A. Katine, J. E. E. Baglin, A. J. Kellock, J. Phys. D: Appl. Phys. 36, 2601 (2003).
[5] S. G. Reidy, L. Cheng, W. E. Bailey, Appl. Phys. Lett. 82, 1254 (2003).
[6] C. W. White, S. P. Withrow, J. M. Williams, J. D. Budai, A. Meldrum, K. D. Sorge, J. R. Thompson, L. A. Boatner, J. Appl. Phys. 95, 8160 (2004).