Magnetic Force Microscopy Probe Research Articles

The role of metal nanoparticles and nanonetworks in alloy degradation

Oxide scale, which is essential to protect structural alloys from high-temperature degradation such as oxidation, carburization and metal dusting, is usually considered to consist simply of oxide phases. Here, we report on a nanobeam X-ray and magnetic force microscopy investigation that reveals that the oxide scale actually consists of a mixture of oxide materials and metal nanoparticles. The metal nanoparticles self-assemble into nanonetworks, forming continuous channels for carbon transport through the oxide scales. To avoid the formation of these metallic particles in the oxide scale, alloys must develop a scale without spinel phase. We have designed a novel alloy that has been tested in a high-carbon-activity environment. Our results show that the incubation time for carbon transport through the oxide scale of the new alloy is more than an order of magnitude longer compared with commercial alloys with similar chromium content.

Parameters of the magnetic force microscope probe optimized for high-resolution measurements

The resolving power of various magnetic probes, which depends on the probe shape and the amount of deposited magnetic material, has been determined by means of computer modeling. The minimum thickness of a cobalt film is experimentally determined, which must be applied to the surface of a filament crystal tip on a nonmagnetic cantilever in order to obtain a magnetic image. It is shown that the point probes with filament crystal tips coated by a thin magnetic film (obtained using a relatively simple preparation method) can provide a spatial resolution comparable with that achieved using cantilevers with magnetic nanoparticles, which require a significantly more complicated preparation procedures.

Calibration of Coercive and Stray Fields of Commercial Magnetic Force Microscope Probes

Variable-field magnetic force microscope (MFM) is introduced to characterize the magnetic behavior of commercially available MFM probes that is relevant to interpret MFM imaging. A Nanotec Electronica S.L. microscope has been conveniently modified to apply magnetic fields in axial direction (up to 1.5 kOe) and in-plane direction (up to 2.0 kOe). Axial and transeverse hysteresis loops of the probes have been generated by measuring the changes in the MFM contrast observed when the magnetic field is applied. The variation of the MFM signal is ascribed to the modification of the magnetic state of the tips. This is enabled by the large coercitivity (~1.7 kOe) of the checked longitudinal recording media. The properties of the probes depend on the coating material, the macroscopic tip shape, and tip radius. In only a few cases, the magnetization of the probe can be oriented along in-plane orientation. In addition, the stray field of the tips has been deduced by measuring the influence of the probe in the magnetic state of the checked samples.

Fabrication of magnetic force microscopy probes via localized electrochemical deposition of cobalt

Magnetic force microscopy probes were obtained via the solution phase electrochemical deposition of cobalt nanostructures at the probe apexes. Single tips were fabricated in an atomic force microscope fluid cell. Multiple tips were produced in a single batch with an alternating potential in an electrochemical cell. The probes achieve 50nm spatial resolution.

Effect of ferromagnetic nanoparticles on the transport properties of a GaMnAs microbridge

A chain of Co nanoparticles was formed along a GaMnAs microbridge by electron beam lithography. The magnetic state of the particles was manipulated by a magnetic force microscope probe. It was found that resistance of the microbridge depended on the state of the particles and was different for the particles in the single-domain and vortex states. The resistance exhibited steplike behavior in an external magnetic field. This behavior was the result of the effect of the inhomogeneous stray fields of the particles on the microbridge resistance. The observed phenomenon can be used as an alternative way to control GaMnAs transport properties.

Interaction of a magnetic vortex with the probe field of a magnetic force microscope

The interaction of a magnetic vortex in a circular ferromagnetic nanoparticle with the probe field of a magnetic force microscope (MFM) is theoretically investigated. In the calculations, the probe field is approximated by the point dipole field. The rigid magnetic vortex model is used to describe the vortex state of magnetization. It is found that the effect of the probe field on the rigid magnetic vortex shell is similar to the effect of a uniform magnetic field parallel to the particle plane. The effect of the Z component of the probe field on the core of the vortex results in mutual probe-vortex attraction or repulsion. It is shown that the magnetization direction of the core of the vortex in the MFM probe field can be changed without a change in the shell vorticity direction.

Focus on nanoscience and nanotechnology

Focus on nanoscience and nanotechnology

Magnetic force microscopy of GaAs:Mn ferromagnetic semiconductors

The dependence of magnetic properties of GaAs:Mn and MnAs epitaxial films grown on GaAs (001) by laser ablation of Mn and undoped GaAs in a hydrogen atmosphere under the growth conditions has been studied by magnetic force microscopy (MFM). Magnetic probe calibration for quantitative MFM measurements was performed by scanning across the slit of the magnetic-head of a tape recorder through which controlled direct current was passed. The dipole approximation was used to describe the magnetic properties of the MFM probe. Nonuniformity of the magnetization of GaAs:Mn films related to the formation of MnAs nanoinclusions, which are ferromagnetic at 300 K, has been observed. The typical scales of the spatial nonuniformity of the magnetization of GaAs:Mn films were varied from 270 to 550 nm depending on the film-growth conditions. The MnAs phase was identified by MFM measurements at an elevated temperature (up to 80°N).

Advantages of CNT–MFM probes in observation of domain walls of soft magnetic materials

The advantage of the CoFe-coated carbon nanotube (CNT) probes in a magnetic force microscope (MFM) is verified on in-plane magnetized soft magnetic materials. CoFe-coated CNT, standard and low-moment MFM probes were used to observe closure domains in square and rectangular Permalloy elements. The perturbative effect of the CNT–MFM probe was far less than that of a standard MFM probe. Domain walls were clearly observed as a pair of dark and bright lines which was in agreement with the micromagnetic simulations. The vortex core was also clearly observed using the CNT–MFM probes.

Detection of magnetic field for measuring current distribution in metal nanostructure

Current induced magnetic field over a metal nanostructure was investigated by using magnetic force microscopy (MFM) to discuss the spatial resolution and the detection current limit in measuring current distribution in a polycrystalline-Si (poly-Si) layer of thin film transistors. It was found that the detection current limit depended on the MFM probe height, which is a separation between the tip and the surface. The optimum probe height for detecting the smallest current avoiding the effect of topography was 16 nm. The detection current limit at the probe height of 16 nm was 29 μA. This technique should be applicable for detecting current distribution in the poly-Si layer.

ＭＦＭ探針による磁壁操作

Magnetic force microscopy (MFM) has been applied to permalloy multistep-semicircular wires containing nearly-free magnetic domain walls (DWs). In this study, we investigated the effect of stray-magnetic fields from the probes in the MFM measurement using low-, medium-, and high-moment probes, which are coated by 12 nm-, 24 nm-, and 72 nm-thick CoPtCr films, respectively. By using the low-moment probe, the DW signal was clearly observed at the side of the wires, which is consistent with a micromagnetic simulation. By using the high and medium moment probes, in contrast, we observed complete and incomplete DW manipulations, respectively. These manipulation signals were found to be maximized immediately above the wire. These phenomena were analyzed by calculating the stray fields from the MFM probes. We also discussed the possibility of the controllable DW manipulation in terms of the stray fields and the MFM scanning sequences.

Magnetic state control of ferromagnetic nanodots by magnetic force microscopy probe

We present the magnetic state control of individual ferromagnetic nanodots under inhomogeneous magnetic field induced by the probe of magnetic force microscope (MFM). Arrays of submicron sized elliptical ferromagnetic Co and FeCr dots with different sizes and periods were fabricated to demonstrate addressable manipulation of magnetization. MFM observations show the magnetization reversal and processes of local remagnetization of individual ferromagnetic nanodots subjected to magnetic change. Computer simulation of magnetization processes under inhomogeneous magnetic field induced by MFM probe was performed on the base of Landau-Lifshitz-Gilbert equation for magnetization.

MFM probe control of magnetic vortex chirality in elliptical Co nanoparticles

Magnetic force microscopy (MFM) methods were applied to investigate the peculiarities of magnetization distribution in elliptical 400×600×27 nm Co particles. Reversible transitions between the uniform and vortex states under inhomogeneous magnetic field of MFM probe were observed. Possibility to control the chirality of a magnetic vortex in these particles by MFM probe manipulation was shown.

Magnetization reversal of ferromagnetic nanoparticles under inhomogeneous magnetic field

We investigated remagnetization processes in ferromagnetic nanoparticles under inhomogeneous magnetic field induced by the tip of magnetic force microscope (MFM) in both theoretical and empirical ways. Systematic MFM observations were carried out on arrays of submicron-sized elliptical ferromagnetic particles of Co and FeCr with different sizes and periods. It clearly reveals the distribution of remanent magnetization and processes of local remagnetization of individual ferromagnetic particles. Modeling of remagnetization processes in ferromagnetic nanoparticles under magnetic field induced by MFM probe was performed on the base of Landau–Lifshitz–Gilbert equation for magnetization. MFM-induced inhomogeneous magnetic field is very effective to control the magnetic state of individual ferromagnetic nanoparticles as well as to create different distribution of magnetic field in array of ferromagnetic nanoparticles.

Ferromagnetic Iron Boride (Fe3B) Nanowires.

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Magnetic force microscopy sensors using iron-filled carbon nanotubes

Probes for magnetic force microscopy (MFM) were prepared by pinning iron-filled multiwall carbon nanotubes to conventional scanning force microscopy probes. These nanotube MFM probes reveal a great potential for high spatial resolution of both topography and magnetic stray field. The ends of the high aspect ratio iron nanowires within the nanotubes can be considered as stationary effective magnetic monopole moments which opens the possibility of quantitative stray field measurements in a straightforward manner. The carbon shells around the iron nanowires provide wear resistance and oxidation protection.

Ferromagnetic Iron Boride (Fe3B) Nanowires

Single-crystal iron boride (Fe3B) nanowires were synthesized on Pt and Pd (Pt/Pd) coated sapphire substrates by a chemical vapor deposition method at 800 °C using boron triiodide (BI3) and iron iodide (FeI2) as precursors. Morphology of the Fe3B nanowires can be controlled by manipulating the Pt/Pd film thickness and the growth time. Transmission electron microscopy and selected area electron diffraction were used to analyze the crystal structures of these novel materials. Electron energy-loss spectroscopy and X-ray energy-dispersive spectroscopy studies on these nanowires confirm that they are composed of boron and iron. Scanning electron microscopy was employed to observe the morphology of these nanomaterials. The typical size of the iron boride nanowires is about 5−50 nm in width and 2−30 μm in length. The vapor−liquid−solid (VLS) growth process is shown to be the growth mechanism of the Fe3B nanowires. Room temperature magnetic force microscopy investigations on the iron boride nanowires suggest that ...

Applications of high-resolution MFM system with low-moment probe in a vacuum

Magnetic force microscopy (MFM) is very useful for observing magnetic domain structures. However, due to stray fields from an MFM probe, observations of small magnetic domain structures are limited. The authors have developed a high-resolution MFM system that utilizes a low-moment probe and a quality (Q)-controlled prove driver, which allows high-quality measurement in a vacuum without disturbing domain structures. Using this system, a resolution finer than 20 nm was achieved. In this paper, the advantages of this MFM are demonstrated using a Permalloy honeycomb nanonetwork and a Permalloy semicircular loop.

Magnetic reversal study of Au-FePt thin films with very high coercivity

Magnetic reversal behaviors of Au (60 nm)-FePt (x nm) thin films with various x values are investigated. A high temperature heat treatment at 800/spl deg/C was applied to obtain an isolated microstructure with L1/sub 0/ FePt particles embedded in a face-centered cubic gold matrix through interfacial diffusion. The coercivity of the thin films was increased from 13.6 kOe to a maximum value of 30.0 kOe as the thickness of the FePt layer was decreased from 200 to 10 nm. From the dc demagnetization and isothermal remanence magnetization measurements, we found that the bilayer sample with x=10 exhibits larger reversible magnetization. The coercive mechanism was found to be controlled by the magnetization rotation of the isolated FePt particles. As x is increased, the reversal behavior is changed into a domain-wall motion mode gradually. The magnetic force microscopy investigations further confirm the change of mechanism. The domain-wall motion appears to result from the formation of large multidomain grains. Considering the relation of reversal behavior and the coercivity, we thus conclude that the removal of domain walls is beneficial for hard magnetic performance.

Absence of weak electron localization in carbon-covered Co-nanowires

We have investigated the low temperature resistance and magnetoresistance behavior of ferromagnetic cobalt wires in perpendicular external magnetic fields of up to B=5 T. Magnetic force microscopy investigations show that the cobalt wires are single-domain at remanence, if the wire width is smaller than about 800 nm. At low temperatures a logarithmic resistance increase is observed which is consistently explained as originating from enhanced electron-electron interaction (EEI) in two dimensions, while the magnetoresistance is dominated by the anisotropic magnetoresistance. Additional resistance corrections due to weak electron localization (WEL) are not observed within the accuracy of our measurements, which is discussed in the framework of recent experimental and theoretical works.