In the last decade since its development, magnetic force microscopy has emerged as a workhorse in imaging magnetic structures at the sub-micron length scales. It possesses the desirable attributes of robustness, straightforward implementation and a fairly well characterized image contrast formation. In recent years, we have successfully implemented MFM in the presence of a highly controlled external magnetic field. Using this technique, it is possible to follow the sampleís magnetic evolution at various points along itís magnetization curve. Further, by using standard software implementation, the images can be presented as an animation of the micromagnetic process. We applied this technique to study a variety of slow varying dynamics of magnetic systems, including the dc erasure of thin film recording media, the mechanisms of moment rotation and reversal, and the domain wall motion nanostructured magnetic elements[4,5].
In this talk, I will first discuss the rudiments of the technique and later show the dynamics of the magnetization of cobalt and permalloy alloys interacting with external fields. Cobalt has a high bulk coercive field and large uniaxial crystalline anisotropy, whereas permalloy has a low bulk coercive field and low crystalline anisotropy. Thus, the behavior of cobalt films would be dominated by the crystalline anisotropy while permalloy would be dominated by the shape anisotropy of the islands. These differences are indeed manifested in the micromagnetics of these systems. I will discuss these and other issues such as multidomain formation, Neel wall motion, Bloch line and cross-tie inclusions, coercivity variations versus aspect ratio, pinning and correlations to individual local hysteresis loops.
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