Magnetic Domain Imaging Research Articles

Magnetic imaging with soft X-ray microscopies

X-ray magnetic circular dichroism yields at inner-core absorption edges large values up to 50%. This serves as huge magnetic contrast mechanism to image magnetic domain structures. The current status of magnetic soft X-ray microscopy providing currently a resolution down to about 20nm to study static domain configurations is demonstrated by selected examples on high magnetostrictive thin films and laterally microstructured elements measured at the XM-I microscope at the ALS (Berkeley CA). Element-specificity allows insight into magnetic coupling mechanisms and the evolution of the domain patterns within full hysteresis loops can be studied by recording the images within external magnetic fields. Both in-plane and out-of-plane configurations of the magnetization can be addressed by tilting the sample at an axis perpendicular to the photon propagation direction. Magnetic X-PEEM measurements obtained at the Swiss Light Source provide complementary information. Spin dynamics, i.e. precession and relaxation of the magnetization, can be addressed by taking into account the inherent pulsed time structure of synchrotrons, First results with a sub-lOOpsec time resolution obtained in a stroboscopic pump-probe experiment with a patterned permalloy element at the XM-1 are reported.

Fabrication and physical properties of permalloy nano-size wires

Nano-size NiFe wires with patterned shapes in half-ring-in-series, octagon-in-series, and zigzag-in-series configurations were fabricated. Their magnetoresistance was studied below room temperature and their magnetic domain images were investigated at room temperature by a magnetic force microscope. In general, we have experimentally demonstrated that the variation of the magnetoresistance of our patterned nano-size wires can be related to different domain configurations and explained by the domain switching effect. The number of magnetic domain walls in our patterned wires can be controlled by the shape anisotropy and the size of each section of patterns that form the wires.

OS05W0267 Evaluation of local work affected layer based on magnetic domain analysis using magnetic force microscopy

This paper deals with the evaluation method of the local work affected layer based on the magnetic domain analysis using a magnetic force microscope (MFM). The fine maze magnetic domain pattern is observed on the lapped ferrite (111) plane. The maze domain pattern becomes coarser by increasing the etched depth of affected surface layer. The area percentage of magnetic domain pattern in the whole lapped surface decreases with an increase of the etched depth and the magnetic domain pattern disappears when the etched depth exceeds about 1μm. This critical value in the etched depth is almost equal to the work affected layer depth, evaluated from electron diffraction analysis. These results show that the magnetic domain imaging method by the MFM becomes a useful technique for evaluating the local work affected layer.

Imaging magnetic domain structures with soft X-ray microscopy

The current achievements in magnetic transmission soft X-ray microscopy will be reviewed. The magnetic contrast is given by X-ray magnetic circular dichroism (X-MCD), i.e., the dependence of the absorption coefficient of circularly polarized X rays on the projection of the magnetization in a ferromagnetic system onto the photon propagation direction. X-MCD contrast can reach, e.g., at L2,3 edges in transition metals, large values up to 50%. Combined with a soft X-ray microscope where Fresnel zone plates acting as optical elements provide a lateral resolution down at 25 nm, it allows for imaging magnetic microstructures. Specific features of this photon-based technique are the recording of images in varying external magnetic fields, an inherent chemical specificity, a high sensitivity to thin magnetic layers, due to the large contrast, and the possibility to distinguish between in-plane and out-of plane contributions. In this report, recent results obtained with the XM-1 microscope at the ALS (Berkeley/CA) demonstrate the broad applicability of this novel experimental technique to both fundamental and technological relevant issues in nanomagnetism. The future potential will be briefly outlined.

Magnetic dichroisms in absorption and photoemission for magnetic characterization in x-ray photoelectron emission microscopy

Magnetic contrast for the operation of a photoelectron emission microscope (PEEM) with synchrotron radiation is provided by magnetic dichroisms. Besides the most frequently employed magnetic dichroism, magnetic circular dichroism in x-ray absorption spectroscopy, energy filtering of photoemitted electrons allows one to also use magnetic dichroisms in photoelectron emission as complementary contrast mechanisms. We demonstrate that it is possible to obtain magnetic contrast in photoemission using PEEM equipped with a simple retarding field electron energy analyzer. Magnetic domain images of an ultrathin film of 10 atomic monolayers of Fe on W(001), obtained by three different contrast mechanisms (circular magnetic dichroism in x-ray absorption, circular magnetic dichroism in Fe valence band photoemission, and linear magnetic dichroism in Fe 3p photoemission) are presented and compared.

Trace analysis for magnetic domain images of L1 0 polytwinned structures

The polytwinned structure in L1 0 FePd alloy is studied by using both conventional TEM and Lorentz microscopy methods. Herein we develop a trace analysis method to determine the surface orientation of a magnetic domain image without the use of electron diffraction patterns. This allows us to analyze magnetization directions.

Feature extraction for magnetic domain images of magneto-optical recording films using gradient feature segmentation

In this paper, we present a method to realize feature extraction on low contrast magnetic domain images of magneto-optical recording films. The method is based on the following three steps: first, Lee-filtering method is adopted to realize pre-filtering and noise reduction; this is followed by gradient feature segmentation, which separates the object area from the background area; finally the common linking method is adopted and the characteristic parameters of magnetic domain are calculated. We describe these steps with particular emphasis on the gradient feature segmentation. The results show that this method has advantages over other traditional ones for feature extraction of low contrast images.

A Monte Carlo Study of Magnetic Domain Images in a Spin-Polarized Scanning Electron Microscope

The magnetic domain images in the spin-polarized scanning electron microscope are studied using a Monte Carlo simulation of electron scattering considering the spin direction of the generated secondary electrons. The variations of the spin polarization of secondary electrons are calculated when the electron probe scans across the magnetic domain boundary of an iron sample. We analyze the primary electron energy and the incident angle dependences of the spatial resolution of the magnetic domain images from the point of view of electron scattering. The shift of the boundary images from the actual magnetic domain boundary is also studied.

Magnetic field calibration of a transmission electron microscope using a permanent magnet material

A new method of assessing the magnitude of the magnetic field in a transmission electron microscope using a permanent magnetic material is described. The approach is versatile and simple enough to be implemented for certain scientific or engineering situations in which the exact calibration of the magnetic field in the microscope column using a small Hall probe may be a problem. We have applied this approach to obtain the magnetic field calibration inside a JEM 3000F field emission electron microscope as a function of the objective lens potential. In the course of this in situ calibration it was not necessary to disassemble the microscope or interrupt its operation. The procedure used is versatile and accurate enough to measure magnetic fields up to 20 kOe (μ0H=2 T in SI units) as was confirmed by subsequent Hall-probe field measurement of the same electron microscope. The calibration method described in this article does not require any special Hall-probe holder adaptations and can be applied to any transmission electron microscope or similar instrument. To illustrate the utility of the technique and its results, quantitative analysis of magnetic domain images obtained with Lorentz microscopy during magnetic reversal of a sample subjected to an in situ magnetic field in the JEM3000F microscope is presented and discussed.

Magnetic domain imaging using orthogonal fluxgate probes

This article presents an application of a miniature orthogonal fluxgate magnetometer to magnetic domain imaging of coated grain-oriented silicon steels. The method is based on a common technique which maps stray magnetic fields emerging from the surface of the silicon steel. An orthogonal fluxgate made of a thin amorphous wire core is bent in a J-shape so that it may work as a gradiometer, in which the longer leg of the J-shaped wire core is made sensitive to stray magnetic fields whereas the shorter one is effectively located at a distance from them. Experiments were carried out with a thin Co-based amorphous wire used as a wire core and a highly grain oriented silicon steel as a sample on which the domain refinement by laser irradiation is made. Well-defined stripe domains with some spike domains, and grain boundaries were clearly imaged with this method without any assisting magnetic field to enhance stray magnetic fields.

Application and future of photoelectron spectromicroscopy

Application examples of imaging type photoelectron spectromicroscopy studies are introduced. One of the imaging type photoelectron spectromicroscopies is micro-ESCA or micro-XPS (electron spectroscopy for chemical analysis; X-ray photoelectron spectroscopy). We connected the modified commercial system (Fisons Instruments, ESCALAB 220i-XL) to the beamlines, which cover the photon energy range of 10 eV–5 keV at the UVSOR facility, Institute for Molecular Science, Okazaki, Japan. It is expected that spatial resolution of 2 μm for the imaging mode and 20 μm for the spectroscopic mode can be achieved. In conjunction with monochromatic and polarized synchrotron radiation light from the UVSOR storage ring, photoelectron spectroscopy studies have been performed, not only for surface science but also for spectroscopy of small samples. Another imaging type of photoelectron spectromicroscopy is known as photoelectron emission microscopy (PEEM). Now commercial PEEM is available with relatively high performance. We report here the example of the combination study of PEEM and X-ray magnetic dichroism spectroscopy for magnetic domain imaging performed at the Photon Factory, KEK, Tsukuba, Japan. Imaging with spatial resolution less than ∼200 nm is now possible using the synchrotron radiation. According to the demands from industrial usage, such as production of magnetic recording media etc., the application method becomes more important. These types of microscope techniques are very valuable, especially in the high brilliant synchrotron light source facility. The future prospects of photoelectron spectromicroscopy are described.

Magnetic intergranular interaction in nanocomposite CoxPt100−x:C thin films

Magnetization reversal and intergranular interactions have been studied in composite CoxPt100−x:C thin films using several magnetic characterization techniques. The intergranular interactions, as determined by ΔM curves, were strongly dependent on the ratio of Co and Pt concentration. For films with high Co content, the intergranular exchange coupling was predominant, while dipolar interactions were exhibited in the film with the equiatomic concentration of Co and Pt. Magnetic intergranular interaction was directly observed using magnetic force microscopy. There is a strong correlation between the value of the ΔM and magnetic correlation length obtained from the magnetic domain images.

Magnetic interface coupling in single-crystalline Co/FeMn bilayers

The magnetic coupling between epitaxial single-crystalline Co and FeMn layers on Cu(001) was investigated by element-resolved magnetic circular dichroism domain imaging using a photoelectron emission microscope. As-grown Co domain patterns reveal the presence of many small domains in the antiferromagnet. The coupling of the Co layer is found to be along $〈100〉$ crystallographic directions. This is discussed in terms of a $45\ifmmode^\circ\else\textdegree\fi{}$ coupling due to frustrations at topological $90\ifmmode^\circ\else\textdegree\fi{}$ domains in the FeMn layer. Coercivity oscillations as a function of FeMn thickness with atomic monolayer period support the importance of such step-induced domains in the coupling.

MAGNETIC MICROSPECTROSCOPY BY A COMBINATION OF XMCD AND PEEM

The benefits of combining soft X-ray magnetic circular dichroism and photoelectron microscopy are demonstrated by applying this combination (XMCD–PEEM) not only to magnetic domain imaging but also to quantitative evaluation of the distribution of spin and orbital magnetic moments. The latter takes full advantage of the spectroscopic aspect of XMCD–PEEM.

Reconstruction of magnetization density in two-dimensional samples from soft X-ray speckle patterns using the multiple-wavelength anomalous diffraction method.

A non-destructive technique for imaging magnetic domains in thin films and two-dimensional magnetic structures using coherent soft X-ray scattering and the multiple-wavelength anomalous diffraction method (MAD) is proposed. The method exploits the strong energy dependence in the magnetic scattering amplitude for 3d transition metals near the L(2,3) absorption edges and 4f elements near the M(4,5) absorption edges. The phase information required in the reconstruction algorithm is derived from the interference between the charge and magnetic scattering amplitudes. Magnetic speckle patterns from the magnetic domain distribution in an artificially defined Fe thin film are used to demonstrate this reconstruction algorithm. Circularly and linearly polarized incident light are examined separately to investigate the effect of polarization on the capability of the method.

Application of commercially available cantilevers in tuning fork Scanning Probe Microscopy (SPM) studies

We describe the construction and operation of an atomic force microscope based on a tuning fork sensor with probe tips obtained from commercially available cantilevers. Only the tip from the cantilever is mounted on the tuning fork, minimizing the change in resonant frequency and the quality factor Q of the tuning fork. The technique allows the use of a variety of commercially available tips for use in different probe microscopy applications like magnetic force microscopy. The compact design of the microscope and its simple feedback electronics make it well suited for operation in novel environments such as at cryogenic temperatures. We present high resolution atomic force images of graphite surfaces, as well as scanning probe images of magnetic domains and Ni dot arrays taken with this microscope.

Magnetic domain imaging of exchange bias system NiO/Cu/NiFe by Kerr microscopy

Two types of magnetic domain structures were observed by Kerr microscopy for the NiO/Cu/NiFe system with different Cu thicknesses. At Cu=8 Å, a frozen-in magnetic structure coinciding with the domain wall at room temperature was observed at variation of external field. At Cu=2 Å, the domain images expand with frustrated domain wall instead.

Room temperature scanning Hall probe microscopy of localized magnetic field fluctuations on the surfaces of magnetic recording media, permanent magnets and crystalline garnet films in external bias fields

A sub-micron room temperature scanning Hall probe microscope (RT-SHPM) was used for real-time imaging of surface magnetic domains of floppy disks, Sr ferrite magnets and Bi-substituted iron garnets placed in large external bias fields. Domain wall nucleation was observed in the garnets where bubble lattices expanded, collapsed and transformed into stripe domains in cyclic bias fields. Evolution of RT-SHPM images was compared with conventional vibrating sample magnetometer measurements.

画像認識手法による磁化特性の評価

Previously, we have proposed a method of image cognition based on the color component decomposing methodology, which has made it possible to cognize each of the human faces even though a different facial expression. Furthermore, we have succeeded in cognizing the monochrome images utilizing light intensity histogram approach.We are now planning to exploit a magnetization characteristics measurement instrument by applying the image cognition method to the Bitter magnetic domain images. As the first step, in this paper, we apply the monochrome image cognition method to the SEM (Scanning type Electron Microscope) images of silicon steel magnetic domains. As a result, it is revealed that the magnetic domain images take the similar ones at the highly saturated region but take the extremely different ones at the not saturated region.

Recent Development and Application of LEEM/PEEM. Magnetic Domain Imaging of Magnetic Nano-structures Observed by Photoemission Electron Microscopy.

We have observed magnetic domains of magnetic nano-structures of nickel by photoemission electron microscopy (PEEM) using synchrotron radiation. The magnetic nano-structures were fabricated by electron beam lithography and lift-off. From the magnetic contrast observed by PEEM and micromagnetic simulations, it is indicated that the square, hexagonal and circular structures form flux closure structures whereas the triangular structure does not form the flux closure structure.