Imaging, Manipulation, and Spectroscopic Measurements of Nanomagnets by Magnetic Force Microscopy

Zhu X., Grütter P.

Magnetic force microscopy (MFM) is a well-established technique for imaging themagnetic structures of small magnetic particles. In cooperation with external magneticfields, MFM can be used to study the magnetization switching mechanism ofsubmicrometer-sized magnetic particles.Various MFM techniques allow the measurementof a hysteresis curve of an individual particle, which can then be compared toensemble measurements. The advantage of using MFM-constructed hysteresis loops isthat one can in principle understand the origin of dispersion in switching fields. It is alsopossible to directly observe the correlation between magnetic particles through carefulimaging and control of the external magnetic field. In all of these measurements,attention needs to be paid to avoid artifacts that result from the unavoidable magnetic tipstray field. Control can be achieved by optimizing the MFM operation mode as well asthe tip parameters. It is even possible to use the tip stray field to locally and reproduciblymanipulate the magnetic-moment state of small particles. In this article, we illustratethese concepts and issues by studying various lithographically patterned magneticnanoparticles, thus demonstrating the versatility of MFM for imaging, manipulation, andspectroscopic measurements of small particles.