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The construction and control of high‐order coupled vortices are a significant challenge for promoting the application of magnetic vortices. Thus far, only double‐coupled vortices have been produced and modulated in some ferromagnetic nanostructures. Here, an effective approach is provided to obtain a high‐order coupled vortex structure by using a chiral nanostructure. Double‐vortex, triple‐vortex, and n‐vortex chains can be successfully constructed using structured Fe4N nanostrips and bias nanomagnets. The designed chiral nanostructure cannot only control the transport and hybridization of vortices but also modulate the domain walls of the vortex chain for spin wave (SW) propagation. At the exciting frequency of 1.2 GHz, the SW propagates along the domain walls formed in the vortex chain. Upon increasing the frequency to 5.0 GHz, the SW gradually spreads from the domain walls into domains. This technique will present a new perspective for the design and application of magnetic vortex‐based devices. [ABSTRACT FROM AUTHOR]

Fe3O4 nanoparticles with crystallite sizes around 10 nm were synthesized by an emulsion method. X-ray diffractometer (XRD) shows that nanocrystalline Fe3O4 possesses face center cubic structure. The magnetic characteristics are investigated by magnetic force microscopy (MFM). Magnetic field directions were applied parallel and perpendicular to the Fe3O4 sample surface for magnetic measurements. Under the perpendicular magnetic field, the phase images of most magnetic nanoparticles exhibit bright or dark MFM contrast. In comparison, the parallel field phase images display a bright–dark dipole MFM contrast, with in-plane magnetic domain configurations. Furthermore, the investigation of strip domains inside Fe3O4 particles under altering magnetic fields indicates the existence of magnetic anisotropy energies, dipole energies as well as inter-grain coupling energies inside the clusters. This approach for probing magnetic responses on nanoscale magnetic domains can be further extended to the analysis of local physical features. [ABSTRACT FROM AUTHOR]

Individual magnetic Fe3O4 nanoparticles were imaged using the developed frequency-modulated magnetic force microscopy (FM-MFM) technique. High-resolution imaging of ac magnetic field from individual magnetic nanoparticles was demonstrated by FM-MFM with a high-coercivity FePt tip. It was found that the amplitude and phase images of ac magnetic field were obtained separately using the technique with a lock-in amplifier. The distribution of magnetic field gradient of the individual nanoparticles is clearly presented. It was observed that magnetic nanoparticles can be more precisely detected by FM-MFM. The results are significant for study of the real magnetic field distribution of individual magnetic nanoparticles (∼20 nm), which provide some valuable information for the analysis of nanoscale magnetic features. [ABSTRACT FROM AUTHOR]

Magnetic force microscopy (MFM) image is directly related to the field derivative distribution above the sample. It is necessary to find the real domain structure of the sample from the MFM image. In this work, the magnetic pole or charge distribution at the sample surface is calculated by deconvoluting the MFM image using the tip's Green function. The Fourier transform of the magnetic potential in the 3-D space above the sample surface can be derived from the Fourier transform of the surface charge distribution. Thus the stray field distribution of sample can be obtained since it is the gradient of the magnetic potential. Based on the stray field distribution and the magnetic properties of the sample, we can analyze the magnetic domain structure. As an example, the domain structure of FeCoZr film is studied. [ABSTRACT FROM AUTHOR]

The alternating current (ac) magnetic field from perpendicular magnetic recording head was imaged by using our developed frequency-modulated magnetic force microscopy (FM-MFM), which uses the frequency modulation of cantilever oscillation caused by applying ac magnetic field to a mechanically oscillated cantilever. The amplitude and phase signals (or orthogonal X and Y signals) of the ac magnetic field can be obtained separately by using the FM-MFM technique incorporated with a lock-in amplifier. A signal transformation technique to characterize the AC magnetic field source for frequency modulated magnetic force microscopy was proposed. Two-dimensional vector analysis together with the magnetization vector rotation of the perpendicular recording head was demonstrated using the FM-MFM method combined with the signal transformation algorithm. By taking advantage of this technique, the present method opens a possibility to stroboscopic analyze the AC magnetic field source and gives a very useful feedback for the development of advanced magnetic recording heads. [ABSTRACT FROM AUTHOR]

In this paper, the influence of the magnetostriction effect on the formation of the stripe domain is studied by micromagnetic simulations. The microstructures and local stress are carefully investigated in soft-magnetic thin films with a thickness from 2 to 256 nm. The domain structures, as well as the M–H loops, of these thin films are calculated by applying the in-plane periodic boundary conditions. It is found that a critical angle \phi0, which is the minimum angle between the magnetoelastic fields Hms in neighbor stripes, exists for the formation of the stripe domains in a thin film. Furthermore, \phi0 depends on the maximum angle between the Hms and the boundary line of neighbor stripes. The second-order derivative of the vertical component of the magnetic stray field which corresponding to the magnetic force microscope signal is also simulated. The M–H loop is calculated in a large thin film with an assumption that the stripe domains are isotropic in-plane. The shapes of these hysteresis loops can also be an indicator of the stripe-domain configuration. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, magnetite (Fe 3 O 4) powders which were obtained by the emulsion method are analyzed to ascertain the structure and mechanism formation of domains in clusters of Fe 3 O 4 nanoparticles. Magnetic force microscopy (MFM) occupies a special niche in the array of techniques which are currently available for imaging magnetic structures of magnetic nanomaterials, yielding high resolution under ambient conditions. The use of MFM in dynamic lift-mode to detect probe–sample interactions from Fe 3 O 4 nanoparticles is reported here to detect and identify the magnetic domains characterization of nanoparticles. The experimental results showed orientation of magnetic domains in the clustering nanoparticles. Finally, an analysis of repulsion and attraction in magnetic field and direction changes of domains formed by magnetite nanoparticles were done. This approach for probing magnetic responses on nanoscale magnetic domains can be further extended to the analysis of local physical features. [ABSTRACT FROM AUTHOR]

Vector analysis from individual Fe 3 O 4 nanoparticles was achieved by magnetic force microscopy (MFM) technique with a micromagnetic modeling, which visualises the vector signals of the magnetic field from Fe 3 O 4 nanoparticles. It is demonstrated that the MFM method combined with micromagnetics can effectively analyze the magnetic charge distribution with varying time. With this technique, the vector distribution of the magnetic field of the individual Fe 3 O 4 magnetic nanoparticles was clearly presented, which will be of great importance for applications in nanobiological systems. [ABSTRACT FROM AUTHOR]