Imaging, manipulation, and spectroscopic measurements of nanomagnets by magnetic force microscopy

Magnetic force microscopy (MEM) is a well-established technique for imaging the magnetic structures of small magnetic particles. In cooperation with external magnetic fields, MFM can be used to study the magnetization switching mechanism of submicrometer-sized magnetic particles. Various MFM techniques allow the measurement of a hysteresis curve of an individual particle, which can then be compared to ensemble measurements. The advantage of using MFM-constructed to that one can in principle understand the origin of dispersion in switching fields. It is also possible to directly observe the correlation between magnetic particles though careful imaging and control of the external magnetic field. In all of these measurements attention needs to be paid to avoid artifacts that results from the unavoidable magnetic tip stray field. Control can be achieved by optimising the MFM operation mode as well as the tip parameters. It is even possible to use the tip stray field to locally and reproducibly manipulate the magnetic-moment state of small particles. In this article, we illustrate these concepts and issues by studying various lithographically patterned magnetic nanoparticles, thus demonstrating the verstality of MFM for imaging, manipulation and spectroscopic measurements of small particles.