Magnetic force microscopy

The magnetic force microscopy (MFM) has been and continues to be one of the primary imaging tools for studying magnetic nanostructures. There are two major issues with the MFM which have been addressed frequently during the last decade: (i) tip-sample interaction and (ii) moderate resolution. Although many techniques have been proposed and developed to resolve these two issues, success is moderate. An ideal tip would be such that the magnetic coating is only performed at the apex of the tip which functions as a point dipole. Various types of techniques have been used to form such kind of MFM tips such as focused ion beam trimming, electron beam induced deposition and selective growth of magnetic material on carbon nanotubes. All these techniques, however, suffer from the shortcomings that the tips cannot be formed in a batch process using the normal sputtering process. In order to address this issue, we have proposed a new type of multilayer tip which does not only allow for batch fabrication but also exhibits a resolution which approaches the theoretical limit. We have developed two types of MFM tips. The first one is based on an AFM/FM coating. In this structure, the exchange bias between AFM and FM greatly improves the stability of the ultrathin FM layer and thus contributes to the resolution enhancement. The second type of tip that we have developed is based on FM/Ru/FM synthetic AFM structures. In this case, we could realize a point-dipole tip without the need to trim the tip or deposit the magnetic layer in a localized region. This significantly improves the resolution.

[1] Liu, Z. Dan, Y. Jinjun, Q. Wu, Y., Magnetic force microscopy using focused ion beam sharpened tip with deposited antiferro–ferromagnetic multiple layers. J. Appl. Phys. 2002, 91 (10), 8843-8845.
[2] Wu, Y. Shen, Y. Liu, Z. Li, K. Qiu, J., Point-dipole response from a magnetic force microscopy tip with a synthetic antiferromagnetic coating. Appl. Phys. Lett. 2003, 82 (11), 1748-1750
[3] Shen, Y. Wu, Y., Response function study of a new kind of multilayer-coated tip for magnetic force microscopy. IEEE transactions on magnetics 2004, 40 (1), 97-100.
[4] Han, G. Wu, Y. Zheng, Y., Dual-synthetic magnetic force microscopy tip and its imaging performance. Journal of magnetism and magnetic materials 2007, 315 (1), 46-52.
[5] Han, G. Wu, Y. Zheng, Y., Double exchange biased magnetic force microscopy tip and comparison of its imaging performance with commercial tips. Japanese Journal of Applied Physics 2007, 46 (7R), 4403.
[6] Han, G. Wu, Y. Zheng, Y. Qiu, J. Li, K., Spacer dependence effect in synthetic magnetic force microscopy tips. Journal of Magnetism and Magnetic Materials 2006, 303 (2), e226-e230.