Magnetic Force Microscopy Probe Research Articles

Magnetic nanowire based high resolution magnetic force microscope probes

We report an efficient process for controlled fabrication of high-resolution magnetic force microscope probes using preformed magnetic nanowires. Nickel and cobalt nanowires produced by electrodeposition were directly assembled onto the tip of a commercial atomic force microscope cantilever with controlled orientation and length by dielectrophoresis. The properties of these nanowire-based probes are characterized.

Magnetic force microscopy investigation of domain structures in Fe–xat.% Ga single crystals (12<x<25)

The domain structure of furnace-cooled (FC) and post-annealed (PA) Fe–xat.% Ga (x=12, 20, and 25) crystals has been investigated by magnetic force microscopy. For both FC and PA Fe–12at.% Ga, the domains were found to be well-aligned and oriented along the [100] direction. For Fe–20at.% Ga, although a preferred [100] orientation remained, a difference in morphology was found between FC and PA conditions—in the PA condition, clear dendritic domains were observed. For both FC and PA Fe–25at.% Ga, a much reduced [100] preferred domain orientation was found, the domain size was notably reduced, and dendrite formation was not observed.

Magnetic nanowire based high resolution magnetic force microscope probes

Magnetic nanowire based high resolution magnetic force microscope probes

MFM Investigation of the Domain Structure of Cobalt Single Crystals

Study of the domain structure at the basal surface of bulk cobalt single crystals was carried out by magnetic force microscopy (MFM). The surface domains were seen in the form of flowers, stars, or circles. The reason for their presence is the reduction of the magnetostatic energy at the cost of a larger total Bloch wall area. The domain structure of bulk cobalt is found to be a transitional one between those observed in bulk materials with low and high perpendicular magnetic anisotropy. The MFM images were correlated with the surface topography recorded by atomic force microscopy (AFM).

A magnetic force microscope using CoFe-coated carbon nanotube probes

Ferromagnetic-film-coated carbon nanotube (CNT) probes were employed in a magneticforce microscope (MFM) observation. We succeeded in making a uniform ferromagneticfilm on the CNT probes by improving the coating process and selecting materials. Theperformance of the CoFe-coated CNT probe was evaluated in ultra-high-density perpendicularmagnetic storage media with densities from 600 to 1100 k flux changes per inch (FCI). Themagnetic domain structure of the magnetic storage media was clearly observed up to1100 kFCI. The ultimate lateral resolution of the newly developed MFM probes is down toabout 10 nm, which exceeds the bit length of a magnetic recording with a density ofTbit inch−2.

Deconvolution processing for increasing the resolution of magnetic force microscopymeasurements

Magnetic force microscopy (MFM) is a widely used form of scanning probe microscopy(SPM) that is used for obtaining a magnetic image from a surface with nanoscaleresolution. Currently, the resolution of MFM is limited to approximately 20 nm due to thelong-range nature of magnetic interactions between the MFM probe’s tip and themagnetic medium. This paper describes an optimal signal processing solutionto the problem of achieving high resolution MFM with the goal of significantlyexceeding the level at which MFM metrology currently performs, thus providingmetrologists with a means of resolution increase that is believed will enable, forexample, the rapid development of high-density magnetic recording media(>100 Gbit in−2). This is achieved by using focused-ion beam trimming of a conventional tip to create aprobe tip of predictable magnetic characteristics and then, provided that the sample couldbe approximated as a thin-film, using knowledge of this tip’s sensitivity field for performinga deconvolution on the measured signal to better estimate the magnetic state of the surfaceunder study. Stated differently, as the MFM measured signal is modelled as the convolutionof the magnetized surface and the tip’s sensitivity field, we exploit knowledge of the tip’sproperties to increase the resolution of the MFM image. Details of the deconvolutionapproach as well as images resulting from this processing are the focus of this paper.

Interplay between shape and magnetocrystalline anisotropies in patterned bcc Fe/Co(001) multilayers

In this work the interplay between magnetocrystalline and shape anisotropies was studied in submicron size particles made of bcc Fe/Co(001) multilayers of thickness 20 nm and Co content in the range 27--75 at. %. Arrays of circular and elliptical particles with well-defined geometry and lateral sizes in the range 150--550 nm were prepared by electron-beam lithography and ion milling and investigated by magnetization measurements and magnetic force microscopy (MFM). The angular dependence of the magnetization of the initial films demonstrates the change of the easy direction of magnetization (in plane) from [100] to [110] as one goes from pure Fe to Fe/Co multilayers with increasing Co content. The first-order anisotropy constant ${K}_{1}$ is negative for the investigated Fe/Co films and depends linearly on the Co concentration. By extrapolation, the change of sign is obtained at about 23 at. % of Co. The high effective magnetic moment of the multilayers, up to $(2.8\ifmmode\pm\else\textpm\fi{}0.3){\ensuremath{\mu}}_{B}$ per atom for the Fe2/Co6 multilayer film, may be explained by an enhancement of the local moments both on Fe and Co and a spin dependent polarization of the electron gas, due to confinement in the individual (0.3--1.2 nm thick) Fe and Co layers. The domain structure and magnetization reversal processes of circular particles (diameter 550 nm) are governed by the shape anisotropy for the nearly isotropic Fe8/Co3 multilayers and by the high magnetocrystalline anisotropy in Fe2/Co6 multilayers. The MFM investigation of elliptical particles with aspect ratio 1:3 reveals that only in the case with cooperating shape and strong magnetocrystalline anisotropies a stable single domain state is formed in the majority (78%) of the elements. From magnetization measurements we deduce that the elliptical particles are in quasisingle domain states (so called C and S states) during magnetization reversal.

Nanometric copper and cobalt clusters deposited using pulsed laser ablation; AFM and MFM investigations

A laser ablation cluster generator, using low energy clusters beam deposition (LECBD), has been developed for synthesis of Cu and Co clusters. These materials have been chosen in order to compare the self-assembling mechanisms of diamagnetic and ferromagnetic clusters on a surface. Aggregates are deposited on silicon substrates under high vacuum. The distributions in size of the Cu and Co clusters have been investigated, in both cases, using atomic force microscopy (AFM) pointing out circular shapes of approximately 8 nm in diameter. Then, magnetic force microscopy (MFM) images are achieved on Co cluster layers and compared with images given by a Co continuous film deposited using conventional pulsed laser deposition.

Magnetic domain structures and stray fields of individual elongated magnetite grains revealed by magnetic force microscopy (MFM)

In order to clarify the relationship between microscopic and macroscopic magnetic features of a rock, we applied magnetic force microscopy (MFM) as a local probe on a sample with an intense natural remanent magnetisation, a norite from Heskestad, Norway. We studied in detail seven magnetite (Fe 3O 4) exsolution lamellae, five of them were about 30 μm long and a few micrometers wide, two were significantly shorter; all were located in their natural host, a grain of clinopyroxene. By combining MFM images of surface magnetisation with information about shape observed with optical microscopy (OM), the internal domain structure was determined for individual grains. In general, the lamellae were pseudo-single-domain grains with open-flux domain magnetisations parallel to their long axes. The domain sizes were, in cross-section, on the order of a micrometer for the longer lamellae and about 300 nm for the short lamellae. By increasing the separation between the MFM probe and the exposed end of the lamellae, information could be obtained about the decrease in stray fields for the individual grains. Close to the lamellae, stray fields were significant even for grains with multiple domains. The largest fields were found above the largest domains. A separation of approximately one domain width was found to be a characteristic distance, where stray fields from adjacent domains begin to cancel one another.

Electron holography quantitative measurements on magnetic force microscopy probes

We report on the quantitative characterization of high-coercivity magnetic force microscopy tips for magnetic images using electron holography. In order to extract quantitative data from the reconstructed phase map, a simulation of the projected flux distribution of the magnetic field of the probe has been obtained considering the simple model of a distribution of macroscopic magnetic dipoles on the tip surface.

Study of the field around magnetic force microscopy probes using electron holography

We have used electron holography to perform quantitative investigations of the leakage flux of thin film tips used as probes in magnetic force microscopy. A method to deduce an arrangement of magnetic domains in a thin magnetic whisker from the knowledge of the stray flux is also described. A simple analytical model of the magnetic properties of the probes allows the extraction of computer images, which simulate the experimental results satisfactory. The reliability of the recorded experimental maps of the magnetic flux arising from these kinds of sensors allows an evaluation of the total flux affecting the sample and the calculation of the magnetic field profile along the tip axis.

Magnetic Force Microscopy Applied in Magnetic Data Storage Technology

AbstractFor Abstract see ChemInform Abstract in Full Text.

Temperature-dependent magnetic force microscopy investigation of epitaxial MnAs films on GaAs(001)

We present variable-temperature magnetic force microscopy (VT-MFM) studies of epitaxially grown MnAs films on GaAs(001). Around a critical temperature of Tc=40 °C, the MnAs film undergoes a first order structural phase transition. Due to the strain involved, ferromagnetic α-MnAs and paramagnetic β-MnAs phases coexist as stripes along MnAs[0001]. The dimensions of the α-phase change from isolated dots at higher temperatures to well ordered stripes at lower temperatures. VT-MFM allows a close look at the evolution of domain patterns of MnAs micromagnets.

Magnetic force microscopy applied in magnetic data storage technology

Microstructured thin-film elements with critical dimensions of 1 μm or less play an increasingly important role in magnetic components for information technology applications. Devices that are directly based on such microstructures are key components in magnetoelectronics for storage and sensor applications as well as modern concepts which are likely to substitute today’s hard disk drives. Basic research on magnetic materials as well as industrial applications create an increasing demand for high-resolution magnetic imaging methods. One such method is magnetic force microscopy (MFM). In spite of considerable achievements, MFM also has some serious shortcomings, which have not been overcome to date. Under normal circumstances, the method yields only qualitative information about the magnetic object and it is difficult to improve the resolution to values below 100 nm. In this paper, we will report on advanced MFM probe preparation, based on electron beam methods, and discuss the possibilities for batch fabrication of such advanced MFM tips. We show that the advanced probes allow high-resolution imaging of fine magnetic structures within thin-film permalloy elements without perturbing them. Additionally, we present high-frequency MFM measurements on a hard disk write head.

MFM imaging of nanowires and elongated patterned elements

Magnetic force microscopy (MFM) studies concerning electrodeposited nanowires are reviewed. It is shown that Co nanowires with 35 nm diameter can exhibit single domain states, opening the way to their potential use as MFM probes. Besides, special attention is devoted to the MFM imaging process of soft magnetic samples. Different observations proving the tip influence when analyzing patterned permalloy elements are presented. Experimental results and numerical simulations using a general framework for reversible perturbations are shown to agree quantitatively.

Magnetic relaxation switches capable of sensing molecular interactions.

Highly sensitive, efficient, and high-throughput biosensors are required for genomic and proteomic data acquisition in complex biological samples and potentially for in vivo applications. To facilitate these studies, we have developed biocompatible magnetic nanosensors that act as magnetic relaxation switches (MRS) to detect molecular interactions in the reversible self-assembly of disperse magnetic particles into stable nanoassemblies. Using four different types of molecular interactions (DNA-DNA, protein-protein, protein-small molecule, and enzyme reactions) as model systems, we show that the MRS technology can be used to detect these interactions with high efficiency and sensitivity using magnetic relaxation measurements including magnetic resonance imaging (MRI). Furthermore, the magnetic changes are detectable in turbid media and in whole-cell lysates without protein purification. The developed magnetic nanosensors can be used in a variety of biological applications such as in homogeneous assays, as reagents in miniaturized microfluidic systems, as affinity ligands for rapid and high-throughput magnetic readouts of arrays, as probes for magnetic force microscopy, and potentially for in vivo imaging.

Quantitative Analysis of the Magnetic Properties of Metal-Capped Carbon Nanotube Probe

Magnetic properties of an individual Fe-alloy-capped nanotube synthesized by catalytic chemical vapor deposition have been investigated for use as probes for magnetic force microscopy (MFM). The remanent magnetization for one unit volume of the Fe-alloy-capped nanotube is 297 emu/cm3 which is comparable to that of a conventional MFM tip. The MFM measurements have been performed using a combination of the Fe-alloy-capped nanotube tip and a frequency modulation detection system in order to improve the sensitivity of MFM.

Computer simulation of magnetic force microscopy images with a static model of magnetization distribution and dipole-dipole interaction

An algorithm for computer simulation of images obtained by magnetic force microscopy (MFM) is suggested. It is based on the Brown formalism and takes into account the shapes and the magnetic properties of the MFM tip and sample studied. The robustness and efficiency of the algorithm are tested by simulating the MFM image of a point magnetic dipole for the case where the tip is approximated by a nonmagnetic truncated cone covered by a thin uniformly magnetized layer. From the computer simulation of the MFM images of the dipole, the optimum parameters of the MFM probe are obtained.

A new theoretical probe for the magnetic force microscope

The magnetic force microscope (MFM) is established as a valuable tool for the analysis of magnetic structures. The standard design of MFM incorporates a silicon tip coated with a magnetic material. However, these tips are subject to several inherent problems, e.g. changing characteristics over time due to damage or magnetic hysteresis. A new theoretical electromagnetic MFM probe is introduced here. Although electromagnetic MFM has been discussed before by Zhou et al. (J. Vac. Sci. Technol. A 17 (1999) 2233), the design presented here is a different approach. Two different probe iterations and their magnetic field intensity distribution are modelled. The probe imaging capability is compared using the reciprocity principle (Wright and Hill, Appl. Phys. Lett. 68 (1996) 1726) to image the simulated force interaction between a sample and the probe fields. Thus, images of a sample's magnetic distribution are produced by the convolution of the different probe gradient field distributions and the sample magnetisation. Both perpendicular and longitudinal magnetisation patterns were simulated with the different probe iterations. This clearly showed the improvement of the second probe iteration, particularly for longitudinal patterns. The practical use of the new probe is also discussed, and future work outlined.

A novel magnetic force microscope probe design

A new theoretical electromagnetic probe for the magnetic force microscope (MFM) is presented here. The magnetic field intensity normal to the probe, H/sub z/(Oe), has been modeled. The reciprocity principle was used to obtain the force acting on the sample due to the probe field when scanned over a magnetic specimen. Thus, images of specimen magnetic distribution were created by the convolution of the distribution and the probe's gradient field. These show that in the case of perpendicular magnetization the new probe was successful. However, in longitudinal magnetization there was an image artifact problem. The practical use of the new probe is discussed, and future work outlined.