Magnetic Force Microscopy — Towards Higher Resolution

Abstract

Abstract. In this chapter Magnetic Force Microscopy is treated in detail. The emphasis is on high resolution and the design and realisation of MFM tips. Principle of MFMThe technique of Magnetic Force Microscopy has been discussed extensively in literature [8,20,12], so we will restrict ourselves to a short description. The principle of Magnetic Force Microscopy is very much alike that of Atomic Force Microscopy -some even dare to mention that MFM is just an AFM with a magnetic tip, much to the dislike of MFM developers because in an MFM much smaller forces are measured. In essence it is true however, and every MFM is capable of AFM as well (the other way round is not true in general).In an MFM the magnetic stray field above a very flat specimen, or sample, is detected by placing a small magnetic element, the tip, mounted on cantilever spring very close to the surface of the sample (figure 1). Typical dimensions are a cantilever length of 200 µm , tip length of 4 µm and diameter of 50 nm and a distance from the surface of 30 nm. The force on the magnetic tip is detected by measuring the displacement of the end of the cantilever, usually by optical means. The forces measured in typical MFM applications are in the order of 30 pN, with typical cantilever deflections in the order of nanometers.An image of the magnetic stray field is obtained by slowly scanning the cantilever over the sample surface, in a raster-like fashion. Typical scan area's are from 1 up to 200 µm with imaging times in the order of 5-30 minutes.

Understanding electrostatic and magnetic forces in magnetic force microscopy: towards single superparamagnetic nanoparticle resolution

“…The varying amplitude during the first pass is a signal for topography changes and the phase shift during the second pass in certain distance shows changes in force gradient. The signals of long range force during the second scan are often indicated by phase because of it local linearity and high signal to noice ratio compared to frequency or amplitude mode [25].…”

Imaging magnetic vortices by magnetic force microscopy: experiments and modelling

“…The difference is very large if The two charge profiles are slightly different but quite similar to the magnetic contrast difference profile. Using a lower lift height, a lower vibration amplitude and a tip coating should lead to a better reproduction of the charge profiles, but this is only possible with an increased sensitivity [32]. It should be finally mentioned that the core contrast could also be obtained, in this case to a good approximation, as the difference between the MFM signals in the absence of perturbation.…”

Magnetic imaging with spin-polarized low-energy electron microscopy

“…-optical microscopies, where magneto-optic Kerr microscopy is one of the most widely known techniques [3,4]; -electron microscopies, including scanning electron microscopy with polarization analysis (SEMPA) [5,6], Lorentz microscopy [7,8], and electron holography [9,10]; -scanning probe microscopies such as magnetic force microscopy (MFM) [11,12], spin-polarized scanning tunneling microscopy (SP-STM) [13], or ballistic emission magnetic microscopy (BEMM) [14,15]; -soft X-rays microscopies, including X-ray photoemission electron microscopy (X-PEEM) [16,17] and scanning transmission X-ray microscopy (STXM) [18,19].…”