Shear-mode magnetic force microscopy with a quartz tuning fork in ambient conditions

We have demonstrated high-resolution shear-mode magnetic force microscopy (MFM) using a quartz tuning fork in ambient conditions. A commercial magnetic cantilever tip was attached to one prong of the tuning fork to realize shear-mode MFM operation. We have obtained MFM images with a spatial resolution of less than 100?nm and demonstrated a frequency resolution of ～1?mHz, values which are achieved by phase shift detection methods.     

Iron-platinum-coated carbon nanocone probes on tipless cantilevers for high resolution magnetic force imaging

High coercivity iron-platinum-coated carbon nanocones (CNCs) have been fabricated for magnetic force microscopy (MFM) by direct-current plasma-enhanced chemical vapor deposition growth of nanocones on tipless cantilevers followed by sputtering and annealing of the FePt film. The FePt-coated CNC probe has many localized magnetic stray fields due to the high-aspect-ratio geometry and small radius of the tip. The MFM imaging on magnetic recording media was performed using CNC probes and compared with the imaging by FePt-coated silicon probes. An image with 20?nm lateral resolution has been demonstrated.     

The advantages of the magnetic structure in ferromagnetic-film-coated carbon nanotube probes

The magnetic structures of ferromagnetic-film-coated carbon nanotube (CNT) probes and conventional pyramidal probes for a magnetic force microscope (MFM) were simulated using three-dimensional micromagnetic simulation. The CNT-MFM probes with a total probe diameter less than 60?nm are almost uniformly magnetized along the longitudinal direction of the CNT, which is the ideal magnetic structure for MFM observations. On the other hand, the pyramidal probes had a vortex structure around the point tip, which suggests that they require a greater thickness of the ferromagnetic film because only part of the magnetic moment participates in the detection of the z-component of the stray field from samples. The advantages of the CNT-MFM probe are uniform magnetization along the longitudinal direction and magnetic imaging ability using a smaller coating thickness.     

Low-noise magnetic force microscopy with high resolution by tip cooling

Low-noise magnetic force microscopy (MFM) was realized by using a conventional high-vacuum MFM with homemade tip-cooling equipment. The noise level of the MFM at a tip temperature of 130 K was estimated at /spl mu/N/m order. High spatial resolution of 10 nm was obtained for observing high-density recording media with recording density of 1000 kfci. The improvement of resolution by tip cooling was a result of the reduction of thermodynamic noise of a cantilever and the effective reduction of tip-sample distance due to the magnetic hardening of a tip.     

Structural and magnetic properties of MnAs/GaAs ferromagnetic semiconductor nanocomposite material

Self-organized (Ga,Mn)As nanoclusters, embedded in GaAs and formed during thermal annealing of Ga_1-xMn_xAs layer at 500 °C or 600 °C, were studied using Transmission Electron Microscopy (TEM) and Magnetic Force Microscopy (MFM). We found that 10–20 nm large NiAs-type hexagonal MnAs nanocrystals gave magnetic contrast in MFM images, whereas smaller zinc-blende nanoinclusions were not visible by means of this technique. Theoretical simulations showed that MFM contrasts reflect interaction between magnetic tip and many randomly distributed MnAs nanocrystals.     

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.     

Magnetic dynamic behavior of nanomagnets studied by Magnetic Force Microscopy with external field

The micro/nanomagnetic behavior of magnetic systems is a key issue as the size of magnetic devices is reduced to or under the micrometer range. We study the magnetic behavior of nanomagnets under different applied magnetic field conditions by Magnetic Force Microscopy (MFM). MFM is sensitive mainly to magnetization distributions that generate magnetic fields. CoCr Magnets were deposited by electropulsed SPM onto a Si substrate with sizes ranging from 400×100 to 800×400 nm and thickness between 2 and 3 nm. MFM measurements were performed using a Digital Instruments (DI) Dimension 3100 SPM upgraded for measurements with an external magnetic field applied to the sample. The home-designed modification consists in an electromagnet with field guides towards the scanning region while measuring. Different magnetic fields up to 400 Oe were applied to the samples in-plane during the MFM measurements. The magnetic configuration for the different applied fields was then imaged by MFM.     

High resolution magnetic force microscopy of patterned L1(0)-FePt dot arrays by nanosphere lithography

High resolution magnetic force microscopy (MFM) has been carried out on L1(0)-FePt dot arrays patterned by plasma modified nanosphere lithography. An ex situ tip magnetization reversal experiment is carried out to determine the magnetic domains and verify the imaging stability of MFM and the mutual perturbations between the magnetic tip and the sample. We have identified that the critical size for the single domain region is about 90?nm across. Comparison with MFM image simulation also suggests that the magnetizations of the triangular dots in both single and double domain states are parallel to one edge of the dots, indicating the large uniaxial magnetocrystalline anisotropy of the L1(0)-FePt phase and the need for decreasing the magnetostatic energy.     

Comparison and Validation of Different Magnetic Force Microscopy Calibration Schemes

The future of consumer electronics depends on the capability to reliably fabricate nanostructures with given physical properties. Therefore, techniques to characterize materials and devices with nanoscale resolution are crucial. Among these is magnetic force microscopy (MFM), which transduces the magnetic force between the sample and a magnetic oscillating probe into a phase shift, enabling the locally resolved study of magnetic field patterns down to 10 nm. Here, the progress done toward making quantitative MFM a common tool in nanocharacterization laboratories is shown. The reliability and ease of use of the calibration method based on a magnetic reference sample, with a calculable stray field, and a deconvolution algorithm is demonstrated. This is achieved by comparing two calibration approaches combined with numerical modeling as a quantitative link: measuring the probe's effect on the voltage signal when scanning above a nanosized graphene Hall sensor, and recording the MFM phase shift signal when the probe scans across magnetic fields produced by metallic microcoils. Furthermore, in the case of the deconvolution algorithm, it is shown how it can be applied using the open‐source software package Gwyddion. The estimated magnetic dipole approximation for the most common probes currently in the market is also reported.     

Intrinsic Switching Field Distribution of Arrays of Ni80Fe20 Nanowires Probed by In Situ Magnetic Force Microscopy

The progress of magnetization reversal of weakly packed ferromagnetic Ni₈₀Fe₂₀ nanowire arrays of different diameters (40, 50, 70, and 100 nm) electrodeposited in polycarbonate membranes was studied by magnetic force microscopy (MFM). For such a low packing density of nanomagnets, the dipolar interactions between neighboring wires can be neglected. The intrinsic switching field distribution has been extracted from in situ MFM images and its width was found to be considerably smaller than for densely packed nanowire arrays.     

Magnetic Force Microscopy of Low-Coercivity Ferromagnetic Nanodiscs

We report the results of magnetic force microscopy (MFM) investigations of low-coercivity Co nanodiscs, with 50 nm lateral size and 20 nm height, fabricated by e-beam lithography and ion etching. We observed two types of MFM contrast in the form of Gaussian and ring distributions caused by strong probe–particle interaction. We compared experimentally the transformation of the MFM contrast from these low-coercivity nanodiscs caused by an external magnetic field applied in situ, and compared the experimental results with theoretical simulations.      

磁力显微镜的发展历史,原理和应用

磁力显微镜（ＭＦＭ）的分辨率高达２０～５０ｎｍ，是纳米尺度磁性材料表面磁结构研究新的有力的工具，本文简单介绍了ＭＦＭ的历史，原理，运作和应用，并介绍了中科院物理所一年来的ＭＦＭ研究，举了两个实例，最后，以ＭＦＭ研究的重要问题作了评论。     

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.     

Numerical simulation of MFM image of a magnetic nano-contact

A MFM image of a magnetic nano-contact is studied numerically. We show that the ring- or arc-shaped MFM images with diameter of the order of 100 nm appear while the size of a nano-contact is of the order of 1 nm. We also show that the origin of the ring or arc-shaped MFM image is the oscillation of the magnetization of a nano-contact induced by the interaction between the MFM-tip and the nano-contact.     

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.     

Field induced vortex dynamics in magnetic Ni nanotriangles

The magnetization states in Ni triangular dots under an applied magnetic field have been studied using variable-field magnetic force microscopy (VF-MFM) imaging. In order to understand their dynamics we performed micromagnetic simulations which are in remarkable agreement with the experimental MFM results. The nanostructures present magnetic vortices as ground states which move under an external magnetic field. The combination of micromagnetic simulations and MFM imaging allows us to identify correctly the vortex chiralities and polarizations. The triangular geometry produces an improved contrast of the vortex core. Additionally, the vortices of different chiralities present clearly different MFM images under an?applied field.     

Fabrication of Coated/Uncoated Magnetic Nanoparticles to Determine Their Surface Properties

Fabrication of coated and uncoated magnetic nanoparticles (MNPs) was achieved in the present study. The preparation and characterization of MNPs were confirmed by Fourier transform infrared spectroscopy (FTIR) spectroscopy, streaming potential (SP), and magnetic force microscopy (MFM) techniques. Coated and uncoated nanoparticles were analyzed by dynamic light scattering method to obtain the mean size of nanoparticles. The SP was used to record the electrical surface charge of nanoparticles. The results obtained revealed that the bare nanoparticles were negative charged at higher pH (pH > 6.0) while coated nanoparticles were positive charged at lower pH (pH < 6.0). The porosity of surface of bare and coated nanoparticles was shown by MFM.     

Resolving magnetic nanostructures in the 10-nm range using MFM at ambient conditions

Following the demand of the magnetic data storage industry, the magnetic structures in hard disk heads are continuously shrinking. This requires a powerful tool to investigate the magnetic properties of these elements in the range of about 10 nm. To achieve this goal, we prepared MFM tips using the electron-beam deposition (EBD) contamination technique, where carbon caps and needles are grown onto the micromachined Si cantilevers. For batch production of MFM tips, however, this technique is not suited well, so we employ the focussed ion-beam (FIB) technique to produce MFM tips with a high aspect ratio similar to those tips with carbon needles. We show that the use of these tips not only improves the lateral resolution, but also considerably reduces the disturbation effects of the weak magnetic structures due to the magnetic tips.     

Measurement of an Iso‐Curie Temperature Line of a Co?Cr?Mo Solid Solution by Magnetic Force Microscopy Imaging on a Diffusion Multiple

The 24 °C iso‐Curie temperature line of a Co? Cr? Mo fcc solid solution is obtained by performing magnetic force microscopy (MFM) imaging on solid solution compositions created in a diffusion multiple. The MFM imaging clearly reveals the boundary that separates the paramagnetic region without magnetic domains from the ferromagnetic region with domains. Compositional analysis along the boundary yields a constant Curie temperature (24 °C) composition line. Such a measurement is more efficient than one‐alloy‐at‐a‐time tests and can be used to screen new ferromagnetic materials.     

Ordering of free-standing Co nanoparticles

Colloidal Co particles of 11 nm diameter were deposited on Si substrate by spin coating and/or casting in magnetic field. A perpendicular magnetic field varying along the diagonal of the substrate was also applied. The samples were analyzed by transmission electron microscopy (TEM), field emission gun scanning electron microscopy (SEM-FEG), atomic and magnetic force microscopy (AFM/MFM). TEM micrographs show local order when a Co nanoparticle monolayer is deposited on Si. Drying the colloidal solution in a magnetic field leads to the formation of quite large clusters (0.3 μm) of Co nanoparticles. A stripe structure was then observed when the particles were deposited by casting in the varying magnetic field. AFM/MFM measurements show isolated Co clusters on the stripes. Magnetic features corresponding to the single Co cluster have been observed pointing out that all magnetic moments in the cluster are oriented along the field direction.