Ions hit magnetism - new challenges for the design of artificial nanostructures

In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation mag¬netization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed [5]. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bi¬layers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.

Refs.:

1. J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
2. J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger,
E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
3. J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord,
L. Schultz, R. Mattheis, Phys. Rev. B 73, 184410 (2006).
4. J. Fassbender, J. McCord, Appl. Phys. Lett. 88, 252501 (2006).
5. M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mücklich, S. Facsko,
J. Fassbender, Phys. Rev. B 75, 220407(R) (2007).