Static and dynamic magnetization processes in magnetic property patterned thin films

The control of the effective magnetic anisotropy, saturation magnetization as well as the dynamic magnetic properties in ferromagnetic thin films is of significant importance for most applications in spin electronics. Usually, the magnetic anisotropy, e.g. uniaxial anisotropy or unidirectional anisotropy (exchange bias), in ferromagnetic single or multi-layers is initialized by applying a magnetic field during film deposition or by a magnetic field anneal, which results in an anisotropy aligned along the applied field direction. The saturation magnetization is mainly determined by the film's composition. Whereas anisotropy and saturation magnetization together determine the precessional frequency of the films, the magnetic damping parameter cannot easily be varied in a controlled way.

We demonstrate different ways to pattern soft magnetic magnetic films in terms of laterally varying magnetic properties [1]. In distinction from conventionally patterned systems, the magnetic behavior of these hybrid property films is strongly influenced by the direct exchange interaction across the (now) magnetic property element's borders. Therefore, the effects are directly correlated with the magnetic feature size. Below a critical magnetic feature size, a transition from a magnetic two-phase material to an effective magnetic meta material occurs. This makes them in some sense comparable to magnetic multilayer structures. However, the lateral 'layers' permit access to spatially resolved characterization methods.

Different samples of anisotropy [1,2], exchange bias [1,3], and saturation magnetization [4] modulated thin films are prepared by local oxidation, introducing local stress variation [5], or local ion irradiation. The magnetization reversal processes in the two-phase materials exhibit unique features, some of them so far only known from magnetic multilayer samples. The main emphasis is on the role of magnetic domain formation and domain wall effects in stripe-like magnetic hybrid structures on the overall magnetization properties. Quasi-cubic anisotropies and bi-directional anisotropies, as well as lateral exchange spring behavior are derived from hysteresis loop measurements and magnetic domain imaging. Effects from the introduced quasi-domains, which are related to the domain wall structure and the corresponding wall interaction, will be discussed. In addition, data regarding the influence of pattern density on precessional frequency and effective damping parameter will be shown.

The presented paths of film preparation provide additional degrees of freedom for the tailoring of magnetic properties and functionality of soft-magnetic thin films. Some of the presented methods allow for a local setting of magnetic properties without irreversible structural and magnetic alterations.

Financial support from the Deutsche Forschungsgemeinschaft DFG is highly acknowledged.

References:

[1] J. Fassbender, J. McCord, J. Magn. Magn. Mat. 320, 579 (2008)
[2] J. McCord, I. Mönch et al., J. Phys. D: Appl. Phys., accepted (2009)
[3] C. Hamann, I. Mönch et al., J. Appl. Phys. 104, 13926 (2008)
[4] J. McCord, L. Schultz et al., Adv. Mat. 20, 2009 (2008)
[5] N. Martin, J. McCord et al., Appl. Phys. Lett., accepted (2009)