Observation Of Magnetic Domain Structures Research Articles

In-situ observation of magnetic domain structures in nanocrystalline soft magnetic materials by differential-phase-contrast scanning transmission electron microscopy

In-situ observation of magnetic domain structures in nanocrystalline soft magnetic materials by differential-phase-contrast scanning transmission electron microscopy

Large topological Hall effect and in situ observation of magnetic domain structures in the Mn2FeSn compound

The search for novel topological magnetic domain structures such as magnetic skyrmions, bubbles and vortices, and relative physical effect has always been the focus of spintronics devices. Here, the magnetism, transport properties and magnetic domain structures of the polycrystalline hexagonal Mn2FeSn compound are studied in detail. We find the strong texture along c-axis in this bulk compound owing to large temperature gradient between the bottom and top of the ingot during the preparation process. The resistivity resulting from topological Hall effect reaches about 5.19 μΩ cm at 50 K in the sample of compound obtained by cutting along perpendicular texture direction. Spontaneous nanoscale magnetic bubbles have directly been observed at low temperature due to the competition among the magnetocrystalline anisotropy, antiferromagnetic, and ferromagnetic exchange interactions as decreasing temperature. It is the formation of non-collinear or non-coplanar spin configuration that causes the obvious topological Hall effect. Additionally, the biskyrmion-like state can be obtained with evolution of stripe domains under an appropriate magnetic field. Based on these results, this study of Mn2FeSn magnet may be beneficial to the development for exploring novel magnetic spin textures.

Microscopic origin of asymmetric magnetization reversal of Co/Pt multilayers with perpendicular magnetic anisotropy

We have comprehensively investigated asymmetric magnetization reversal behaviors of (x-Å Co/7.7 Å Pt)5 multilayers (x = 3.1 and 4.7) with perpendicular magnetic anisotropy. Our direct observation of magnetic domain structures by means of magneto-optical microscopy reveals that the asymmetry arises both from nucleation and wall-motion processes. An asymmetric nucleation behavior is observed, which could be originated from the preexisting non-reversed domains which might have a reproducible or random spatial distribution, controllable by tuning the field profile. An asymmetric wall-motion behavior stemming from asymmetric stripe domain evolution is also observed.

Direct observation of multiple magnetic transitions in the La3NiGe2-type compounds

By using Lorentz transmission electron microscopy, we show the real-space observation of magnetic domain structures in orthorhombic polycrystalline (Tb1−xGdx)3NiSi2 (x = 0, 0.4) compounds. The significant changes in magnetic domains related to multiple magnetic transitions were identified. A spin reorientation transition was further studied and a type of magnetic domain structure with two mutually perpendicular domain walls was observed, where the magnetic vortices and antivortices appeared as an array. This magnetic domain pattern evolves with temperature, which corresponds well to the spin reorientation transition and is related to the change in ferromagnetic and noncollinear magnetic components.

Development of a scanning soft X-ray spectromicroscope to investigate local electronic structures on surfaces and interfaces of advanced materials under conditions ranging from low vacuum to helium atmosphere.

A scanning soft X-ray spectromicroscope was recently developed based mainly on the photon-in/photon-out measurement scheme for the investigation of local electronic structures on the surfaces and interfaces of advanced materials under conditions ranging from low vacuum to helium atmosphere. The apparatus was installed at the soft X-ray beamline (BL17SU) at SPring-8. The characteristic features of the apparatus are described in detail. The feasibility of this spectromicroscope was demonstrated using soft X-ray undulator radiation. Here, based on these results, element-specific two-dimensional mapping and micro-XAFS (X-ray absorption fine structure) measurements are reported, as well as the observation of magnetic domain structures from using a reference sample of permalloy micro-dot patterns fabricated on a silicon substrate, with modest spatial resolution (e.g. ∼500 nm). Then, the X-ray radiation dose for Nafion® near the fluorine K-edge is discussed as a typical example of material that is not radiation hardened against a focused X-ray beam, for near future experiments.

Lorentz TEM study of the magnetic microstructure in near-eutectoid Co-Pt alloys

Abstract In this paper, we report Lorentz Transmission Electron Microscopy (LTEM) observations of magnetic domain structures in a near-eutectoid Co 40 Pt 60 alloy. The crystallographic microstructure is characterized using conventional bright field/dark field TEM imaging. The magnetic induction orientation inside magnetic domains is extracted from Fresnel through-focus images by reconstructing the phase of electron wave using the transport-of-intensity equation. The alloy shows a nano-chessboard pattern composed of the L10 tetragonal and L12 cubic phases. The magnetization distribution in four neighboring L10 tiles in the nano-chessboard structure is found to follow a vortex/anti-vortex configuration to reduce the magnetostatic and magneto-crystalline anisotropy energies. An unconventional domain wall referred to as an inter phase magnetic domain wall (IPMDW) is observed at the inter-phase boundaries of L10 and L12 phases. Magnetic domain walls in other microstructures (tweed microstructure, macro-twinned structure, coarsened L10 plates) are also documented.

Foucault optical system by using a nondedicated conventional TEM

We have constructed an electron optical system for both Foucault imaging and small‐angle electron diffraction (SmAED) modes by using a nondedicated conventional transmission electron microscope. The objective lens is switched off as for Lorentz microscopy. An objective mini‐lens is utilized in order to make a crossover on the plane where a selected area aperture is located. The aperture works for an angular selection in the Foucault mode. The present electron optical system has two advantages: one is the independent control of the illumination and the imaging optics, and the other is the application of external magnetic fields to the specimen parallel to the optical axis with the objective lens. In SmAED mode, the maximum camera length is estimated to be approximately 1300 m. We succeeded in the observation of magnetic domain structures and SmAED patterns of the rhombohedral phase of La0.7Sr0.3MnO3 by using the present electron optical system. Copyright © 2016 John Wiley & Sons, Ltd.

Photographic observation of magnetic domain structure with three-dimensional local magnetization direction

The direction of magnetization of a magnetic material is possibly oriented three-dimensionally because of the presence of magnetic anisotropy field, self-demagnetizing field, and stray field. Therefore, the three-dimensional detection of the direction of magnetization is required. The method of magnetic domain observation by photographic imaging utilizing the Kerr effect is widely used. If the perpendicular magnetization components exist, there is a problem that obliquely incident light has superimposed longitudinal Kerr and polar Kerr effects. To perform the three-dimensional detection of magnetization direction, it is necessary to eliminate the influence of the polar Kerr effect from the Kerr effect of obliquely incident light. We report the photographic observation of the magnetic domain structure and the detection of the three-dimensional local magnetization direction using the Kerr effect, applying only an in-plane saturation magnetic field.

Effect of annealing on exchange stiffness of ultrathin CoFeB film with perpendicular magnetic anisotropy

The effect of annealing on the exchange stiffness of ultrathin CoFeB films with perpendicular magnetic anisotropy was investigated through the observation of magnetic domain structures by magneto-optic Kerr-effect microscopy. A significant reduction of the exchange stiffness after an annealing process was observed, which is in striking contrast to a previous report that studied thick CoFeB films with in-plane magnetic anisotropy. Our results suggest that interdiffusion of non-magnetic atoms from the adjacent layer into CoFeB layer reduces the exchange stiffness, which explains the difference between the annealing effect on ultrathin and the thick CoFeB films. Thus, it is critical to prevent annealing-induced interdiffusion in order to suppress undesired sub-volume switching that degrades thermal stability of a free-layer in spin-transfer torque magnetic random access memory.

Observation of magnetic domain structure in anatase (Ti,Co)O2 thin film at room temperature

Magnetic domain structures in anatase (Ti,Co)O2 (001) epitaxial thin films were observed at room temperature. Magnetic force microscopy in vacuum enabled to observe submicrometer-sized maze domain. Variation of magnetic domain structure as functions of carrier density and Co content was in accordance with that of macroscopic magnetization representing close relationship between the bulk magnetism and magnetic domain structure. With increasing carrier density and/or Co content, the magnetic domain became larger with larger magnetic force signal mostly, where the ferromagnetic transition at carrier density of ∼2 × 1019 cm−3 was observed as an emergence of magnetic domain structure. Micromagnetic parameters were evaluated as functions of carrier density and Co content.

Investigation of Microscopic Demagnetization Process Using Magneto-Optical Microscopy

Detailed demagnetization process depending on various external field profiles has been investigated using a magneto-optical Kerr/Faraday microscopy for a Co/Pt multilayer film with a perpendicular magnetic anisotropy. By quantitatively analyzing local magnetic domain structures, we propose that it is possible to define a parameter η, which represents how well the demagnetization has been carried out microscopically. The degree of demagnetization η, defined by a ratio between the final demagnetized image intensity and saturated image intensity, has been experimentally found to significantly reflect the microscopic demagnetization behavior. Dependences of η on the maximum amplitude, decreased step size, and effective sweeping rate of alternating demagnetizing field have been systematically investigated together with a direct microscopic observation of magnetic domain structures.

GMI in Nanostructured FeNi/Ti Multilayers With Different Thicknesses of the Magnetic Layers

Nanostructured multilayers are proposed as a competitive alternative to magnetoimpedance (MI) thick films. However, the effect of the thickness of the magnetic layers on the properties of MI multilayers is still unclear. To perform a systematic study, three multilayered structures consisting of magnetic <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Fe}_{20}{\rm Ni}_{80}$</tex></formula> layers and nonmagnetic Ti layers were prepared by sputtering. In each structure, FeNi layers have different thickness (25, 50, and 100 nm) keeping the same total thickness. Magnetic measurements and magnetic domain structure observations were used for the characterization of the samples. The MI of FeNi/Ti- based multilayers was evaluated in terms of the magnitude of the impedance variations and its sensitivity with respect to the applied magnetic field. The results show that the multilayer with 50 nm FeNi layers has a slightly better properties than the sample with a 100 nm FeNi layers, while the sample with a 25 nm thick FeNi layers performs considerably worse. The sample <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$[{\rm FeNi}(50\ {\rm nm})/{\rm Ti}(6\ {\rm nm})]_{7}/{\rm FeNi}(50\ {\rm nm})$</tex></formula> displays a MI ratio of 24% at 200 MHz and a sensitivity of 135 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\%{\rm kAm}^{-1}$</tex></formula> at 140 MHz.

Domain structure, magnetic properties, and giant magnetoimpedance of FeNi/Ti‐based multilayers

AbstractMagnetic multilayers consisting of magnetic FeNi and non‐magnetic Ti layers were prepared by rf‐sputtering. Magnetic measurements and magnetic domain structure observations were used for characterization of the samples. The magnetoimpedance performance of FeNi/Ti‐based multilayers is evaluated in terms of the magnitude of the effect and its sensitivity with respect to applied magnetic field. The results show that the trilayer with Ti layer of 6 nm (sample A), deposited to avoid the possibility of appearance of a trascritical state, performs better than the sample with a 10 nm Ti layer (sample B). The best results are obtained with [FeNi/Ti]5/FeNi multilayered structure (sample C) reaching a value of about 60% of variation of the impedance at 180 MHz and a sensitivity of about 22%/Oe at 180 MHz.

Observation of magnetic domain structures in epitaxial MnAs film on GaAs(001) with temperature hysteresis

The saturation magnetization of MnAs films epitaxially grown on GaAs(001) substrates exhibited temperature hysteresis in the temperature range of 10–45 °C. We investigated the cause of the temperature hysteresis using temperature- and field-controlled magnetic force microscopy (MFM). The MFM results showed that inside the ferromagnetic α-MnAs stripes of the film at 30 °C, 180° domains were formed during cooling but a single domain state was developed during heating. Despite the cooling procedure, a single domain state was found inside the α-MnAs stripes when a magnetic field of 800 Oe was applied. From these results, the spontaneous magnetization of the α-MnAs phase was ascribed to the temperature hysteresis.

Real-space observation of magnetic domain structure at metamagnetic tansition in a triple-layer ruthenate Sr4Ru3O10

We report the real-space observation of magnetic domains in the ac-plane at the metamagnetic transition in a triple-layer ruthenate Sr4Ru3O10 by magneto-optical imaging and scanning Hall probe measurements. We find anisotropic magnetic domain structures with weak c-axis correlation at low fields. The magnetic inhomogeneities are removed above the metamagnetic transition field. These changes of magnetic structure support the phase-separation scenario for the ultra-sharp steps in magnetoresistance.

Observation of Magnetic Domain Structure in Fe&lt;SUB&gt;81&lt;/SUB&gt;B&lt;SUB&gt;15&lt;/SUB&gt;Si&lt;SUB&gt;4&lt;/SUB&gt; Amorphous Alloy by Lorentz Microscopy and Electron Holography

Effects of heat treatment, with and without an external magnetic field, on the magnetic properties of Fe 81 B 15 Si 4 amorphous specimens are investigated by Lorentz microscopy and electron holography. These observations are used to clarify the details of magnetizing processes in the specimens. It is found that heat-treatment with an external magnetic field increases the magnetic anisotropy, while that without reduces the magnetic anisotropy. It is considered that this difference results from the alleviation of the strain field by heat treatment and the induced magnetic anisotropy caused by heat treatment with a magnetic field.

Development and Application of Magneto‐Optical Microscope Using Polarization‐Modulation Technique

AbstractMagneto‐optical (MO) effect is commonly used not only for an observation of magnetic domain structures, but also for a research of electrical structures in magnetic materials. In addition, distribution of a magnetic flux diverging from a magnetized sample and/or distribution of a current in the sample can be visualized with the help of an MO‐indicator film placed on the sample. In order to obtain quantitative information of the flux distribution we have developed an MO microscope using a polarization‐modulation technique. Utilizing the MO microscope with a magnetic garnet film as an indicator we have obtained a quantitative image of current distribution in a superconducting film. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Observation of magnetic domain structure in Terfenol-D by scanning electron acoustic microscopy

The magnetic domain structure in oriented Tb 0.3Dy 0.7Fe 1.92 (Terfenol-D) is investigated by scanning electron acoustic microscopy (SEAM) in a wide frequency range from 75 to 530 kHz. Both secondary electron image and electron acoustic image can be obtained in situ simultaneously. By changing the modulation frequencies, the SEAM can be used as an effective nondestructive method to observe not only the surface topography and domain structure but also the subsurface domain structure and defects. The magnetic domain structure is verified by magnetic force microscopy (MFM). Furthermore, magnetic domains can be observed in both linear and nonlinear imaging modes by SEAM. The contributions to the image contrast are related to the signal generation through the piezomagnetic coupling mechanism, magnetostrictive coupling mechanism, and thermal-wave coupling mechanism.

High-resolution observations of temperature-dependent magnetic domain structures withinGaxMn1−xAsby Lorentz microscopy

The observation of magnetic domain structures within an in-plane magnetized ${\mathrm{Ga}}_{x}{\mathrm{Mn}}_{1\ensuremath{-}x}\mathrm{As}$ dilute magnetic semiconductor on the submicronmeter scale by Lorentz microscopy is described. A micronmeter-scale domain substructure is found to be characteristic of the micromagnetics of the ${\mathrm{Ga}}_{x}{\mathrm{Mn}}_{1\ensuremath{-}x}\mathrm{As}$ sample. Due to the competition of temperature-dependent biaxial and uniaxial anisotropy, conventional zigzag and unusual segmented domain structures are identified, with the latter exhibiting spontaneous reorganization with varying temperature. The experimental results are compared with micromagnetic simulations.

Simultaneous observation of magnetic domain structure and topography of Fe70Co30 using scanning Lorentz force microscopy

The surface topography and the distribution of stray magnetic flux density of Fe70Co30 are observed simultaneously by using scanning Lorentz force microscopy (SLFM). The SLFM images of the magnetic domain of Fe70Co30 have been observed repeatedly, and they were found to be unaffected by the surface roughness and friction force. As compared to the magnetic force microscopy image, it can be inferred that small stray magnetic flux loops were detected near the sample surface in the SLFM image.