Switching Magnetization Magnetic Force Microscopy — An Alternative to Conventional Lift-Mode MFM

Abstract

In the paper we present an overview of the latest progress in the conventional lift-mode magnetic force microscopy (MFM) technique, achieved by advanced MFM tips and by lowering the lift height. Although smaller lift height offers improved spatial resolution, we show that lowered tip-sample distance mixes magnetic, atomic and electric forces. We describe an alternative to the lift-mode procedure -Switching Magnetization Magnetic Force Microscopy [SM-MFM], which is based on two-pass scanning in tapping mode AFM with reversed tip magnetization between the scans. We propose design and calculate the magnetic properties of such SM-MFM tips. For best performance the tips must exhibit low magnetic moment, low switching field, and single-domain state at remanence. The switching field of such tips is calculated for Permalloy hexagons.

Removal of electrostatic artifacts in magnetic force microscopy by controlled magnetization of the tip: application to superparamagnetic nanoparticles

“…The same CM-MFM instrumentation can be also used to distinguish the electrostatic and magnetic signals in MFM images of relatively hard ferromagnetic samples, the stray field of which could orient the domains of the tip, thus reducing the effectiveness of the tip demagnetization procedure. Indeed, a magnetic field with intensity − H rs , tip can be applied and switched off after the first scan, following a procedure analogous to that used in SM-MFM 25 26 or in differential MFM 27 . A second MFM image is recorded with the probe magnetized along the opposite direction with respect to the first one ( Fig.…”

“…In switching magnetization MFM (SM-MFM), proposed by Cambel et al . 25 26 , the analyzed surface is scanned twice in tapping mode, with opposite tip magnetization orientations, obtained by applying an opportune magnetic field before each scan. If the magnetization state of the sample is not affected by the external field applied to invert the probe magnetic moment and by the magnetic field induced by the tip during the measurements, reversing the probe magnetization results in the inversion of the detected magnetic contrast while the atomic and electrostatic contributions remain unchanged.…”

Single nanoparticles magnetization curves by controlled tip magnetization magnetic force microscopy

“…These factors can be summarized as: i) the low magnetic moment, which produces a low magnetic tip-sample interaction, close to the sensitivity limit of the technique; ii) the presence, in MFM images, of an additional signal due to electrostatic tipsample interactions (i.e., van der Waals, electric charge, capacitance coupling), which has been demonstrated to be of the same order of magnitude in respect to the magnetic one 35 ; iii) the lack of an unambiguous theoretical model describing the tip-sample (NP) interaction consistently with experimental data and the consequent difficulty in converting the detected MFM signal to the quantitative value of a physical parameter, such as the magnetic moment of a single nanoparticle. Some methods to remove the electrostatic effects in MFM images have been proposed, such as the combined use of Kelvin probe force microscopy and MFM, proposed by Jaafar et al 54 , or the switching probe magnetization MFM and the differential MFM, proposed by Cambpel et al and Wang et al, respectively [55][56][57] . Recently, we proposed a new MFM technique, called controlled magnetization-MFM (CM-MFM), with the aim of depurating the MFM signal from the electrostatic artifacts and detecting the signal due to the sole magnetic tip-NPs interactions 58 .…”

Magnetic imaging using geometrically constrained nano-domain walls

“…Finally, other approaches involve modification of the MFM technique rather than the magnetic probes, e.g. imaging the same sample twice but with the probe magnetized in opposite directions 34,35 ; driving the probe at different frequencies during topography and lift scans 36,37 , or using dual probes where one of the probes is non-magnetic and records the topography signal, while the second one (at higher distance from the surface), records the magnetic signal 38 . However, none of the solutions mentioned above fully addresses all the aforementioned challenges.…”