Use Of Magnetic Force Microscopy Research Articles

Compelling Evidence for the Role of Retained Austenite in the Formation of Low Cycle Fatigue Extrusions in a 9Ni Steel

The 9Ni martensitic steels have a martensitic microstructure which contains retained austenite after solution heat treatment and water quenching. Under low cycle fatigue, extrusions formed at the surface of the material and were very close to martensite lath boundaries. The presence of retained austenite at martensite laths has been highly suspected to impact the cyclic plasticity. However, the nano-size of the austenitic phase makes it difficult to obtain clear evidence of its role. The paper focuses on the precise determination of these extrusions and the link with the retained austenite. The paper also emphasizes the innovative and promising use of magnetic force microscopy (MFM) to document cyclic plasticity of a 9Ni steel. It is shown that electron microscopies, even the most advanced ones, may be unsuccessful in reaching this goal, while magnetic force microscopy (MFM) overcame the difficulty. This technique has allowed imaging of both the extrusion and the retained austenite. These analyses confirm that the fatigue extrusions originated from a local displacement of martensite lath. The proposed mechanism, in which the retained austenitic film acts as a lubricant film or greasy film promoting a flowing of martensite along the interfaces, is unambiguously demonstrated.

Magnetic force microscopy characterization of core–shell cobalt-oxide/hydroxide nanoparticles

Cobalt-based nanoparticles directly synthesized on conductive substrates through electrodeposition find application in a broad range of scientific and technological fields.The capability to characterize both morphological parameters (e.g., shape, size, structure, and numerical density per unit of area) and magnetic properties (e.g., magnetic moment, saturation magnetization, or coercivity) directly on the substrate on which they are grown is fundamental for many of those applications. In this work, we report on the use of magnetic force microscopy (MFM) to characterize Co-based nanoparticles synthesized through electrodeposition on Al substrates using two different counter electrodes, i.e., Co and Pt. Morphological analysis using AFM and scanning electron microscopy (SEM) was used to assess differences in size and number density of the nanoparticles obtained using the two counter electrodes, while MFM was employed to measure the remanent magnetization of single isolated nanoparticles, to asses the presence of a nonmagnetic shell on the nanoparticles and to estimate their thickness.

Magnetic domains characterization of clusters of magnetite nanoparticles

In this paper, magnetite (Fe3O4) powders which were obtained by the emulsion method are analyzed to ascertain the structure and mechanism formation of domains in clusters of Fe3O4 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 Fe3O4 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.

MFM Study of a Sintered Nd–Fe–B Magnet: Analyzing Domain Structure and Measuring Defect Size in 3-D View

This paper describes the use of magnetic force microscopy (MFM) to investigate the domain structure of sintered Nd–Fe–B magnet in a thermally demagnetized state. Observations are made at both perpendicular and parallel surfaces to the alignment axis (easy axis). Clear magnetic contrast images in 3-D view with defined domain structures are presented. Mazelike magnetic domains and stripe magnetic domains are observed in the perpendicular and parallel surfaces, respectively. Superficial spike domains and reverse spikes are observed within the main domains and analyzed in 3-D view. MFM images illustrate the grains of Nd–Fe–B magnets, and indicate the multi-domain structures within individual grains. The effect of interfacial defects upon the domain structure is studied in 3-D, and evident reverse magnetic domains (nucleation sites) are observed on the imperfection region. The height and width of the defect region are determined using the XEI imaging software. In addition, the volume and surface area of nucleation region are evaluated and validated theoretically by developing an approach involving coercivity versus the nucleus volume. Defect regions have been identified by using Raman spectroscopy as an oxide in character rather than metallic. The average domain width and domain wall energy have been determined for both directions.

Magnetic Force Microscopy in Liquids.

In this work, the use of magnetic force microscopy (MFM) to acquire images of magnetic nanostructures in liquid environments is presented. Optimization of the MFM signal acquisition in liquid media is performed and it is applied to characterize the magnetic signal of magnetite nanoparticles. The ability for detecting magnetic nanostructures along with the well-known capabilities of atomic force microscopy in liquids suggests potential applications in fields such as nanomedicine, nanobiotechnology, or nanocatalysis.

Visualization of Electric Current Flow by Use of Magnetic Force Microscopy

We present a two-dimensional (2D) imaging of electric current flow in nanoscale range obtained for planar structures. Experiments were performed at current densities of 10 5 -10 6 A/cm 2 for ∼ 1-μm-wide current-carrying metal- lic stripe. The images were obtained by use of magnetic force microscopy (MFM) as a sensor to measure a mag- netic response of current flow. The 2D current mapping was reconstructed from MFM phase images by numerical inver- sion of Biot-Savart law. By using such method, we obtained the parallel and perpendicular components of the current as well as module of total current with the spatial resolu- tion better than 100 nm. We clearly observed the changes of X and Y components of current density related to changes in the cross-section or form of the structures. Developed magneto-transport techniques can be used for detection and control of the current flow in real nano-electronic devices for studying of defects of current paths in nano-stripes due to, for example, electromigration processes and in other applications.

Pulse force nanolithography on hard surfaces using atomic force microscopy with a sharp single-crystal diamond tip

AFM-based technique of nanolithography is proposed. The method enables rapid point by point indentation with a sharp tip. When used in tandem with single-crystal diamond tips, this technique allows the creation of high aspect ratio grooves in hard materials, such as silicon or metals. Examples of fabricated groove arrays on Si surface with 30–100nm pitches and 5–32nm depths are presented. Cutting of a 63nm thick metal magnetic film is demonstrated. The resulting structure is studied by the use of magnetic force microscopy.

Magnetic configurations of Co(111) nanostripes with competing shape and crystalline anisotropies

Nanostripes with varying widths are lithographed on Co thin films with strong magnetic anisotropy resulting from the epitaxial growth onto vicinal Si(111) substrate. The competition between magnetocrystalline and shape anisotropies is used to tune the magnetic behavior of Co nanostripes. Single domain configuration is observed for nanostructures where magnetocrystalline and shape anisotropies go along the same direction. However, more complicated configurations such as open stripe domains can be developed when both anisotropies compete. The nanostructures have been experimentally characterized by longitudinal magneto-optical Kerr effect and magnetic force microscopy (MFM). Micromagnetic simulations performed by finite-element and finite difference codes are in good agreement with the experimental results. The use of MFM based techniques such as the variable field magnetic force microscopy and the so-called three-dimensional modes has allowed us to follow the evolution of the domains and domain walls under externally applied magnetic fields, i.e., to deeply understand the magnetization reversal process in the multidomain nanostripes. In particular, the nanostripes with competing anisotropies and a high aspect ratio present vortex configuration along the domain walls which have a key role in the magnetization reversal process.

New insights into the use of magnetic force microscopy to discriminate between magneticand nonmagnetic nanoparticles

Magnetic force microscopy (MFM) is a very powerful technique, which can potentially beused to detect and localize the magnetic fields arising from nanoscopic magnetic domains,such as magnetic nanoparticles. However, in order to achieve this, we must be able to useMFM to discriminate between magnetic forces arising from the magnetic nanoparticles andnonmagnetic forces from other particles and sample features. Unfortunately, MFM canshow a significant response even for nonmagnetic nanoparticles, giving rise topotentially misleading results. The literature to date lacks evidence for MFMdetection of magnetic nanoparticles with nonmagnetic nanoparticles as a control.In this work, we studied magnetite particles of two sizes and with a silica shell,and compared them to nonmagnetic metallic and silica nanoparticles. We foundthat even on conducting, grounded substrates, significant electrostatic interactionbetween atomic force microscopy probes and nanoparticles can be detected, causingnonmagnetic signals that might be mistaken for a true MFM response. Nevertheless, weshow that MFM can be used to discriminate between magnetic and nonmagneticnanoparticles by using an electromagnetic shielding technique or by analysis ofthe phase shift data. On the basis of our experimental evidence we propose amethodology that enables MFM to be reliably used to study unknown samplescontaining magnetic nanoparticles, and correctly interpret the data obtained.

Magnetic force microscopy of iron oxide nanoparticles and their cellular uptake

Magnetic force microscopy has the capability to detect magnetic domains from a close distance, which can provide the magnetic force gradient image of the scanned samples and also simultaneously obtain atomic force microscope (AFM) topography image as well as AFM phase image. In this work, we demonstrate the use of magnetic force microscopy together with AFM topography and phase imaging for the characterization of magnetic iron oxide nanoparticles and their cellular uptake behavior with the MCF7 carcinoma breast epithelial cells. This method can provide useful information such as the magnetic responses of nanoparticles, nanoparticle spatial localization, cell morphology, and cell surface domains at the same time for better understanding magnetic nanoparticle-cell interaction. It would help to design magnetic-related new imaging, diagnostic and therapeutic methods.

Reversible magnetic domain-wall motion under an electric field in a magnetoelectric thin film

We report direct microscopic measurements that confirm the magnetic stripe-domain patterns can be reversibly changed under an electric field due to the converse magnetoelectric effect in a bilayer thin film ferromagnetic-Ni/ferroelectric-lead zirconate titanate (100nm∕1.28μm) heterostructure. Electric field-induced curving, bending, branching, and elongation of magnetic stripe-domain patterns in the Ni layer are observed with the use of magnetic force microscopy. Upon removal of the electric field, the magnetic stripe-domain patterns return to their original configuration, i.e., reversible.

Magnetic Force Microscopy of Superparamagnetic Nanoparticles

The use of magnetic force microscopy (MFM) to detect probe-sample interactions from superparamagnetic nanoparticles in vitro in ambient atmospheric conditions is reported here. By using both magnetic and nonmagnetic probes in dynamic lift-mode imaging and by controlling the direction and magnitude of the external magnetic field applied to the samples, it is possible to detect and identify the presence of superparamagnetic nanoparticles. The experimental results shown here are in agreement with the estimated sensitivity of the MFM technique. The potential and challenges for localizing nanoscale magnetic domains in biological samples is discussed.

Scanning probe microscopy on magnetic colloidal particles

We report some first results on magnetite and iron nanoparticles studied with atomic force microscopy (AFM). AFM images the particles on a smooth substrate, and their lateral diameter, height and polydispersity are determined and discussed. The use of magnetic force microscopy (MFM) on such small particles is explored both experimentally and theoretically. We present models which allow to estimate with MFM the magnetic moment of a single superparamagnetic nanosphere, which cannot be done with other techniques.

Imaging Carbon Nanotubes in High Performance Polymer Composites via Magnetic Force Microscopy

Application of carbon nanotubes as reinforcement in structural composites is dependent on the efficient dispersion of the nanotubes in a high performance polymer matrix. The characterization of such dispersion is limited by the lack of available tools to visualize the quality of the matrix/carbon nanotube interaction. The work reported herein demonstrates the use of magnetic force microscopy (MFM) as a promising technique for characterizing the dispersion of nanotubes in a high performance polymer matrix.