Direction detectable static magnetic field imaging by frequency-modulated magnetic force microscopy with an AC magnetic field driven soft magnetic tip

Abstract

Direction detectable static magnetic field imaging, which directly distinguishes the up and down direction of static perpendicular magnetic field from a sample surface and the polarity of magnetic charges on the surface, was demonstrated for CoCrPt-SiO2 perpendicular magnetic recording media based on a frequency-modulated magnetic force microscopy (FM-MFM), which uses a frequency modulation of the cantilever oscillation induced by an alternating force from the tip-sample magnetic interaction. In this study, to generate the alternating force, we used a NiFe soft magnetic tip driven by the ac magnetic field of a soft ferrite core and imaged the direction and the amplitude of the static magnetic field from the recorded bits. This method enables measurement of the static magnetic field near a sample surface, which is masked by short range forces of the surface. The present method will be effective in analyzing the microscopic magnetic domain structure of hard magnetic samples.

Magnetic force microscopy using tip magnetization modulated by ferromagnetic resonance

“…where m z(dc) and m z(ac) are the amplitude of the dc component and ac component of the magnetic dipole, respectively [5].…”

“…However, in lift-mode MFM, it is difficult to image the magnetic domain structure at a small tip-sample distance because of the superimposition of interaction forces such as van der Waals and electrostatic forces induced by the sample surface on the magnetic interaction force. As an alternative, MFM with a soft magnetic tip driven by an ac magnetic field was proposed to separate the magnetic interaction from the van der Waals and electrostatic interactions [5]. Direction detectable static magnetic field imaging was demonstrated; however, this method of MFM is not applicable to soft magnetic materials because of the use of the external magnetic field.…”

Magnetic Force Microscopy on Nanofibers—Limits and Possible Approaches for Randomly Oriented Nanofiber Mats

“…Naturally, electrospun nanofiber mats are not the only samples with high surface roughness. Saito et al and Cao et al reported MFM measurements on an Sr ferrite sintered magnet with an extremely high roughness of approximately 1 µm [87][88][89]. This is a similar order of magnitude that can be estimated in typical electrospun nanofiber mats in which nanofibers, typically with diameters of some hundred nanometers, are positioned on top of each other with large pores through which lower layers are accessible.…”

“…In addition to using sophisticated methods such as the A-MFM described in [87][88][89], this example shows that measuring MFM on surfaces with high roughness is possible even with common equipment, suggesting transferring these approaches to nanofiber mats. The next approach for investigating electrospun magnetic nanofiber mats should, thus, be based on partially oriented nanofiber mats, as they can be produced by electrospinning on fast rotating cylinders such as counter electrodes, they can be utilized to start parameter optimization from such samples between ordered and chaotic structures, they can be used for attaining deeper understanding, and finally for finding the optimum tip, lift height and AFM parameters for measuring even more random nanofiber mats.…”

Magnetic domain structure imaging near sample surface with alternating magnetic force microscopy by using AC magnetic field modulated superparamagnetic tip

“…In order to address this issue a few MFM methods have been developed to extract the magnetic force signals near the sample surface. These techniques include torsional resonance mode MFM with a Co 80 Cr 20 hard magnetic tip [17], switching magnetization MFM with a permalloy soft magnetic tip [18], ferromagnetic resonance MFM with a FePt hard magnetic tip [19], bimodal MFM with a commercially available CoCr hard magnetic tip [20], and alternating MFM (A-MFM) with a NiFe soft magnetic tip [21], etc. Among these methods, the modulation method shows advantages for extracting magnetic force signals and increasing force sensitivity near the sample surface.…”