A uniaxial anisotropy is observed in many thin magnetic layer systems. Consequently the magnetization processes along varios directions are different. A typical example is the so called shape anisotropy which favors an in-plane magnetization for thin magnetic films. In addition there are many other origins for the occurrence of a uniaxial anisotropy contribution; for example, the film preparation conditions (in an applied magnetic field), the symmetry of the substrate, the strain of the film and interface effects. Uniaxial anisotropy contributions can be modified by means of ion irradiation in an applied magnetic field. The underlying mechanisms are as manifold as the origins of the different anisotropy contributions. An ion induced modification of a perpendicular interface anisotropy was first observed in the case of Co/Pt multilayers .
In the following an ion induced modification of the uniaxial anisotropy is shown exemplarily for an amorphous ferromagnet (see Fig. 1). Due to a temperature treatment in an applied magnetic field the ferromagnet exhibits an in-plane uniaxial anisotropy. A part of the ferro-magnet is covered with a resist mask, so that only the uncovered areas are irradiated with ions in an applied magnetic field which is oriented to the initial hard magnetization direction. Consequently the atoms rearrange and the easy magnetization direction of the uniaxial anisotropy follows the externally applied magnetic field direction. This procedure can be performed on a µm scale which leads to so called "anisotropy-patterned" layers.
a) A CoFeSiB layer with a uniaxial magnetic anisotropy is covered partially with a mask. Only areas which are not covered (circles with d = 20 µm) are penetrated by the He ions. The ion irradiation was performed in a magnetic field applied along the originally hard magnetization direction. Consequently a locally varying anisotropy is found which is shown schematically in b).
1. Planar patterned magnetic media obtained by ion irradiation
C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet
Science 280, 1919 (1998).
2. Magnetic anisotropy and domain patterning of amorphous films by He-ion irradiation
J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt
Appl. Phys. Lett., 86, 162502 (2005).
3. Materialien - magnetische strukturiert
Pressemitteilung FZ Dresden-Rossendorf vom 17.05.2005 (http://www.hzdr.de/db/Cms?pOid=20570&pNid=3438)
1. Magnetic properties and domain formation in amorphous films anisotropy patterned by ion irradiation
J. McCord, J. Fassbender, M. Frommberger, M. O. Liedke, R. Schäfer, E. Quandt
International Magnetics Conference, Intermag 2005, Nagoya, Japan. (Link to pdf)