Search

Studies on local conduction paths in composite electrodes are essential to the realization of high-performance sulfide all-solid-state lithium batteries. Here, we directly evaluate the electrical p...

Studies on local conduction paths in composite electrodes are essential to the realization of high-performance sulfide all-solid-state lithium batteries. Here, we directly evaluate the electrical properties of individual LiNi1/3Mn1/3Co1/3O2 (NMC) electrode active material particles in composite positive electrodes by scanning probe microscopy (SPM) techniques. Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM) were combined. The results indicated that all NMC particles exhibit a charged state with increasing potential, but low electronic conduction paths exist at point contacts of some NMC particles. Furthermore, the I-V characteristics measured by conductive-atomic force microscopy (C-AFM) suggest that these specific NMC particles show low charge-discharge reactivity. The results of the SPM techniques indicate that poor conduction locally limits the charge-discharge reactivity of electrode active materials, leading to the degradation of battery performance. Such SPM combination accelerates the morphological optimization of composite electrodes by facilitating the investigation of the intrinsic electrical properties of the electrodes.

A latent scratch which is an extremely shallow scratch induced on a SiC wafer during chemo-mechanical polishing (CMP) has been investigate by mirror projection electron microscopy (MPJ), low-energy scanning electron microscopy (LESEM), atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM). The latent scratch, which is difficult to detect by using optical microscopes, was easily visualized by MPJ as a high contrast dark line. The morphology of detected latent scratch is less than 1nm in depth and about 30nm in full width at half depth by AFM evaluation. The STEM observation revealed the latent scratch was accompanied two dislocation arrays. One contains loop-like dislocations and the other contains spiky dislocations, both lying in the wafer at a few ten nm in depth.

In the era of Big Data and the Internet of Things, data archiving is a key technology. From this viewpoint, magnetic recordings are drawing attention because they guarantee long-term data storage. To archive an enormous amount of data, further increase of the recording density is necessary. Herein a new magnetic recording methodology, "focused-millimeter-wave-assisted magnetic recording (F-MIMR)," is proposed. To test this methodology, magnetic films based on epsilon iron oxide nanoparticles are prepared and a focused-millimeter-wave generator is constructed using terahertz (THz) light. Irradiating the focused millimeter wave to epsilon iron oxide instantly switches its magnetic pole direction. The spin dynamics of F-MIMR are also calculated using the stochastic Landau-Lifshitz-Gilbert model considering all of the spins in an epsilon iron oxide nanoparticle. In F-MIMR, the heat-up effect of the recording media is expected to be suppressed. Thus, F-MIMR can be applied to high-density magnetic recordings.

UTokyo Research掲載「強力な磁石を観察できる顕微鏡プローブの開発」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/microscopy-probe-can-observe-strong-magnets.html, UTokyo Research "Microscopy probe can observe strong magnets" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/microscopy-probe-can-observe-strong-magnets.html

A pair of magnetic domain walls (DWs) in ferromagnetic NiFe rings has been investigated in terms of the magnetic force microscopy (MFM). When the distance between the rings d is greater than a threshold value dth, MFM signals indicate that a DW in the ring is dragged due to a stray magnetic field from an MFM probe tip. When d < dth, this drag signals disappears; DWs are bound to each other by the DW-DW interaction. This transition can be argued in terms of the competition between the DW-DW magnetostatic interaction and the DW-drag potential. From the d-dependent MFM data, the DW-drag potential was estimated.

We developed a magnetic force microscope (MFM) where magnetic fields were applied by orthogonal electromagnets. This equipment can be used to observe magnetic domains by specifying an arbitrary angle while applying an external magnetic field of 5 kOe or less. A dot and a rectangular thin film made of permalloy were measured with this equipment. The chirality of the vortex state in the permalloy dot could be determined by using this apparatus. Furthermore, the shape of the closure domain changed every time the direction of the magnetic field was changed by 45 degrees. These results are discussed in detail together with the micromagnetics simulations.

Magnetic force microscopy (MFM) has been applied to permalloy multistep-semicircular wires containing nearly-free magnetic domain walls (DWs). In this study, we investigated the effect of stray-magnetic fields from the probes in the MFM measurement using low-, medium-, and high-moment probes, which are coated by 12 nm-, 24 nm-, and 72 nm-thick CoPtCr films, respectively. By using the low-moment probe, the DW signal was clearly observed at the side of the wires, which is consistent with a micromagnetic simulation. By using the high and medium moment probes, in contrast, we observed complete and incomplete DW manipulations, respectively. These manipulation signals were found to be maximized immediately above the wire. These phenomena were analyzed by calculating the stray fields from the MFM probes. We also discussed the possibility of the controllable DW manipulation in terms of the stray fields and the MFM scanning sequences.

Regularly aligned arrays of magnetic nano dots buried in silicon wafers have been fabricated using damascene technique with the help of electron beam lithography. Arrays of square, rectangular, cross-shaped and Y-shaped structures of submicron size have been obtained. Spin distributions have been observed by means of magnetic force microscopy and analyzed by a micromagnetic simulation with Landau–Lifshitz–Gilbert equations. Importance of magnetostatic interactions working between adjacent dots has been elucidated.

Magnetic force microscopy (MFM) with a low moment probe and Q-control in a vacuum was applied to a permalloy semicircular wire loop with a single magnetic domain wall (DW). We successfully observed a nearly free single DW in such a nanomagnet, which is easy to move even using weak magnetic fields. In the case of MFM measurement with a high moment probe, the effects of the probe's stray field caused "DW manipulation," and the MFM signal was maximized just above the wire. When using the low moment probe, the MFM signal was maximized at the side of the wire, which concurs with the result of micromagnetic simulation.

We have developed a new scanning mode and an aligned carbon nanotube tip for atomic force microscopy (AFM) for measuring the critical dimension of deep structures. The aligned carbon nanotube (A-CNT) was assembled in the scanning electron microscope (SEM) chamber. The diameter of the tip is uniformly around 20 nm and the tip attachment angle is within ±1.5° to the sample normal. The aspect ratio (length/diameter) of the tip is greater than 30. The new scanning mode is composed of two functions, namely transporting the tip along the steep trench structure and detecting the sample surface. This mode can faithfully trace the steep side wall using a flexible CNT tip without damaging the tip. The critical dimension (CD) measurements of the shallow trench isolation (STI) were performed using the newly developed scanning mode and the A-CNT tip.

Magnetic structures and magnetization processes in a permalloy wire-based honeycomb network were investigated by means of magnetic-force microscopy (MFM) and magnetoresistance measurement. The MFM measurements show that the remanent magnetic structures are governed by a magnetic interaction similar to the ice-rule, which provides a direct analogy between the present honeycomb network and an Ising system on a kagome lattice. The magnetoresistance measurements reveal that the magnetic interaction at the vertexes also dominates the magnetization processes in the network. With a decrease in the exchange energy at the vertices, the ice-rule-type interaction disappears, causing a transition of the magnetization distribution in the network.

Magnetic force microscopy (MFM) is a useful tool for investigating magnetic recording media, ferromagnetic patterns and magnetic devices. Ultra-thin magnetic coating probes were developed with the aim of providing high-resolution MFM. High-sensitivity MFM system with quality factor auto control (QFAC) was developed for use with such thin magnetic coating probes. We studied performance of the QFAC system in air and in vacuum. As a result, we found this is a powerful technique for imaging a magnetic domain. The QFAC in vacuum was superior to that in air. We observed finer magnetic domains than those observable with a conventional MFM system. This paper, we reports experimental results for ultra-high-density recording media; we estimate the lateral resolution is less than 20 nm.

さまざまな条件でシリコーン処理を施した電子線硬化ポリウレタンフィルムの表面物性を調査するとともに, これらの試料を用いて走査型プローブ顕微鏡の高分子表面摩擦力試験機としての応用の可能性を検討した. 高分子フィルム試料として, シリコーンを用いて表面性を制御した電子線硬化ポリウレタンアクリレートを調整した. これらフィルム試料の表面ケイ素量と表面自由エネルギーとの間に線形関係があることを確認した. また, 工業規格試験法による摩擦係数との間にもほぼ線形な関係があることが確認された. ここで得た試料を用い, 走査型プローブ顕微鏡によるミクロスケールでの表面摩擦力の測定を行った結果, ミクロスケールの摩擦力と表面自由エネルギーとの間に, シリコーン処理方法, 試料の種類に依存せず明瞭な線形関係が成立することを見いだした. さらに, ミクロスケールとマクロスケールの摩擦力との間にも相関関係が認められた.

Regularly aligned arrays of submicron-sized Y-shaped permalloy (Ni80Fe20) structures buried in silicon wafers have been fabricated. Spin distributions of the surface have been observed using a magnetic force microscope (MFM) and analyzed by a micromagnetic simulation based on the Landau–Lifshitz–Gilbert equation. In widely-spaced linear arrangement of dots, two magnetic poles on the ends of two of three arms and a multi-domain structure in the remaining arm were observed. On the other hand, in the closely-spaced honeycomb arrangement regularly aligned magnetic poles appeared at the ends of all arms and no multi-domain structures appeared and the ‘spin ice’ states were confirmed at each vertex site of the Y-shaped dot.

In this paper, we report on the observed magnetic spin structure and the micromagnetic simulation of Y-shaped permalloy (Ni80Fe20) arrays. The arrays were fabricated using the damascene technique, with electron-beam lithography. For a widely separated linear arrangement, magnetic poles are observed on the ends of two of three arms of the Y-shaped array and multidomains on the remaining arm. For a closely separated honeycomb arrangement and a pair of antisymmetrical dots (termed mirror dots), regularly aligned magnetic poles are observed. It is suggested that the honeycomb array or mirror dots have a strong magnetostatic interaction. The calculated spin distributions approximately correspond to the magnetic force microscopy (MFM) images, in good agreement with the experimental results.

Magnetic force microscopy (MFM) is very useful for observing magnetic domain structures. However, due to stray fields from an MFM probe, observations of small magnetic domain structures are limited. The authors have developed a high-resolution MFM system that utilizes a low-moment probe and a quality (Q)-controlled prove driver, which allows high-quality measurement in a vacuum without disturbing domain structures. Using this system, a resolution finer than 20 nm was achieved. In this paper, the advantages of this MFM are demonstrated using a Permalloy honeycomb nanonetwork and a Permalloy semicircular loop.

Transition between a vortex magnetic state and a uniform magnetic state in a Ni 81 Fe 19 mesoscopic ring has been investigated in terms of resistive-noise spectroscopy. The observed low-frequency noise exhibits critical enhancement around the magnetization saturation. This noise enhancement can be argued from the viewpoint of the critical phenomena due to the chiral-symmetry breakdown of mesoscopic magnetic-structure, which can present a typical mechanism of symmetry transition of magnetic structure in mesoscopic ferromagnets.

A method for detecting the helicity of magnetic-moment distribution in vortex states in a ferromagnetic mesoscopic ring has been developed. This method involves measuring an asymmetric component of the resistivity distribution as a function of the external field. This field-induced asymmetry reflects the direction of the magnetic-moment circulation via the anisotropic magnetoresistance effect, which allows precise measurements of magnetic structures.

The magnetic properties of a Ni 81 Fe 19 honeycomb nano-network have been investigated by magneto-resistance measurements and magnetic-force microscopy. The results indicate that the magnetic properties of remanent state and the magnetic process in the network is governed strongly by magnetic interactions at the vertexes.

A method to control the direction of the magnetic-moment circulation in ferromagnetic nanoscale rings is presented. This method involves controlling the domain-wall (DW) motion using the gradient of the DW energy along the circumference in cooperation with an external magnetic field. Since it is free from the DW pinning and depinning process, the method is applicable even under strong thermal disturbance. Magnetic-force-microscopic observation was performed for Ni81Fe19 rings 500 nm in diameter in which the gradient of the DW energy was introduced by decentering the rings. The result indicates perfect controllability of the magnetic-moment circulation at room temperature, demonstrating its potential for a wide range of applications in magnetic memory devices.

The magnetic domain configuration in a submicron Ni81Fe19 wire network has been investigated by magnetic force microscopy. To improve the responsivity of the magnetic force microscope, an active quality factor autocontrol method was adopted. In the remanent state, domain walls were observed trapped firmly at the vertexes of the network. The magnetic domain configurations appear to minimize the exchange energy at the vertexes. These results indicate that the magnetic property of the ferromagnetic network can be described in terms of the uniform magnetic moments of the wires and interwire magnetic interactions at the vertexes. The observed structure of the domain walls is well reproduced by micromagnetic simulations.

Spin-polarized radio frequency (RF) currents and RF-Oersted fields resonantly excite a magnetic vortex core confined in a micron-scale soft magnetic disk. In this study, we measured the rectifying voltage spectra caused by the anisotropic magnetoresistance oscillation due to the gyration of the vortex with different polarity and chirality. The measured spectra are presented such that we can determine the vortex properties and strength of the spin torques and Oersted field accurately and directly through analytical calculation., Comment: 39 pages,1 table, 10 figures

Nanostructured ferromagnets provide a variety of well-defined magnetization configurations. The symmetry of these configurations in a ferromagnetic nanostructured ring can be altered by an external magnetic field in a controllable manner. We found, by means of resistive-noise spectroscopy, that the chiral-symmetry breakdown of a micromagnetic configuration accompanies a critical fluctuation of the magnetization distribution analogous to a second-order phase transition.

The micromagnetics and galvanomagnetic effects in Permalloy honeycomb nano-network were investigated using magnetic force microscopy (MFM) and magnetoresistance measurements. MFM showed that the magnetic properties of the system can be analyzed as a frustrated system constructed by magnetic moments in the wires. It was also observed that the magnetic properties of the system corresponds to the Ising spin model with a kagome lattice. Also from magnetoresistance measurements, it was clarified that the system behaves as a nanoscale ice-rule system which governs the magnetization switching process. But the ice rule type interaction disappeared with reducing magnetic energy at the vertices.

Magnetic force microscopy is performed on Permalloy honeycomb nanonetwork and Permalloy semicircle wire loop using low momentum probe Q-control in vacuum. The new method is executed without disturbing the magnetic domain structure of the samples.

Direct observation of the dynamics of a single domain wall (DW) in a NiFe-Cu nanowire is investigated. This reveals that such a topological particle indeed has a very small but finite mass of 6.6/spl times/10/sup -23/ kg, and interacts with high-frequency ac electric currents by exchanging momentum. This measurement is made possible by observing resonance of a single DW in which DW motion induced by a oscillating electric current in a tunable potential is used. The dominant mechanisms in these nanowires arise from the exchange coupling between the local magnetization and the spin of conduction electrons. The first mechanism is due to the reflection of conduction electrons by the DW, called momentum transfer. The other is the transfer of the spin angular momentum from conduction electrons to the DW as the electrons pass through the DW. This spin-transfer effect is proportional to the spin polarization of the current.

A magnetic domain wall (DW) is a spatially localized change of magnetization configuration in a magnet. This topological object has been predicted to behave at low energy as a composite particle with finite mass1. This particle will couple directly with electric currents as well as magnetic fields, and its manipulation using electric currents2,3,4,5,6,7,8 is of particular interest with regard to the development of high-density magnetic memories9. The DW mass sets the ultimate operation speed of these devices, but has yet to be determined experimentally. Here we report the direct observation of the dynamics of a single DW in a ferromagnetic nanowire, which demonstrates that such a topological particle has a very small but finite mass of 6.6 × 10-23 kg. This measurement was realized by preparing a tunable DW potential in the nanowire, and detecting the resonance motion of the DW induced by an oscillating current. The resonance also allows low-current operation, which is crucial in device applications; a DW displacement of 10 µm was induced by a current density of 1010 A m-2.

The magnetic anisotropy and the magnetization reversal process of a nanometer-scale FeNi antidot array system of triangle lattice were investigated at room temperature by means of torque and resonating-sample magnetometries. The magnetic anisotropy of the system has a sixfold rotational symmetry refracting the structural symmetry of the array of holes. The magnetic anisotropy energy between the hard and easy axes is about 3.2 × 10 4 J / m 3 .

The magnetoresistance in an FeNi submicron-structure comprising two wires of 80 and 200 nm in width connected in series was measured at 77 K . When the external magnetic field was applied parallel to the wire axis, two switching fields corresponding to the distinct coercive force of the two wires were observed. When the external magnetic field was applied at an angle of θ >30° to the wire axis one switching field was observed, indicating simultaneous magnetization reversal in both wires. This indicates that the domain-wall trapping around the joint can be controlled systematically in terms of the direction of the external magnetic field.

A magnetic vortex core confined in a micron-scale magnetic disk is resonantly excited by both spin-polarized rf current and rf field. We found that rectifying voltage spectra caused by the resonance of vortex core are dependent not only on the core polarity, but also the chirality. These experimental results can be explained by analytically calculating the anisotropic magnetoresistance effect induced by the motion of the vortex core.

A magnetic vortex core confined in a micron-scale magnetic disk is resonantly excited by spin-polarized radio-frequency (rf) current and rf field. We show that rectifying voltage spectra caused by the vortex core resonance is dependent on the core polarity. Rectifying voltage spectra are given by the superposition of the polarity-dependent term and the polarity-independent term. The sign of the polarity-dependent rectifying voltage reverses when the sign of polarity P or external field H is reversed. This experimental result can be explained by the anisotropic magnetoresistance effect caused by the vortex core motion.

The magnetic properties of two-dimensional network comprising a Permalloy wire-based honeycomb structure were investigated by magnetic force microscopy and magnetoresistance measurement. These results indicate that the magnetization of the wire behaves homogenously like a binary bit and that the magnetic interaction at the vertex governs this magnetization. This allows us to achieve a magnetoelectronic device, based on the magnetic interaction among the wires.

The magnetic structure and magnetization process in a permalloy wire-based honeycomb network have been investigated by means of magnetic-force microscopy (MFM) and magnetoresistance measurement. The MFM measurements show the remanent magnetic structures to be governed by magnetic interaction similar to the ice rule, which provides a direct analogy between the present honeycomb network and an Ising system on a kagom\'e lattice. The magnetoresistance measurements reveal that this interaction also dominates the magnetization processes in the network. By decreasing the exchange energy at the vertices of the network, the ice-rule type of interaction causes a transition of the magnetization process in the network.

The external-magnetic-field dependence of the Aharonov–Bohm oscillation in a ferromagnetic Fe19Ni81 nanoring was measured. The amplitude of the Aharonov–Bohm oscillation is suppressed above the magnetization saturation, which can be argued in terms of the magnetic flux density in the ring body. In the vicinity of the magnetization saturation, the oscillation almost vanishes, which is relevant to the magnetic fluctuation affected by the competition between the shape magnetic anisotropy and the external magnetic field.

The magnetic domain configurations and the magnetization processes in a permalloy wire-based honeycomb nano-network have been investigated by means of magnetic-force microscopy and magnetoresistance measurement. The magnetic structure is mainly governed by the magnetic interaction among the magnetic pole on the vertices, being similar to the so-called “ice-rule.” The magnetization vector in a wire behaves coherently. The present results seem to give a direct analogy between the honeycomb network and an Ising system on a kagome lattice. The ice-rule type interaction, however, disappears with reducing magnetic energy at the vertices.

The high-vacuum atomic force microscope (HV-AFM) is a useful tool that is used in various sample environments and achieve good Z axis sensitivity in a noncontact mode operation because the cantilever is free from hydrodynamic damping. The instrument is designed with the aims of minimizing the measuring time, simplifying the operation and achieving high performance. A pumping pressure of about 10-4 Pa is obtainable within 15 min. To achieve easy operation, the optical lever deflection detection head is placed outside the vacuum chamber. The vibration isolation is achieved using an elastic damper and a magnetic-floating-type turbomolecular pump. This vibration isolation method works well enough to obtain the atomic-resolution image of a highly oriented pyrolytic graphite (HOPG) sample. We checked the sensitivity of the instrument using the noncontact mode of operation of a magnetic force microscope (MFM). The Z axis sensitivity in vacuum operation was compared with that in ambient operation. The quality factor increased by more than 25 times and the Z axis sensitivity increased by more than 10 times in vacuum operation (10-4 Pa).