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We propose an electric measurement technique for the magnetic anisotropy field of ferromagnetic thin films and their tiny patterned structures, particularly, in the case of in-plane magnetic anisotropy. This technique measures the anomalous Hall resistance by sweeping the angle or strength of the external magnetic field. The magnetic anisotropy field can be determined explicitly from the linear dependence of the Hall resistance on the angle and strength of the external magnetic field. The present technique can be applied to both ferromagnetic thin films and their patterned magnetic structures with small volumes, overcoming the signal resolution limit of conventional techniques.

Interface engineering is an effective approach to tune the magnetic properties of van der Waals (vdW) magnets and their heterostructures. The prerequisites for the practical utilization of vdW magnets and heterostructures are a quantitative analysis of their magnetic anisotropy and the ability to modulate their interfacial properties, which have been challenging to achieve with conventional methods. Here we characterize the magnetic anisotropy of Fe3GeTe2 layers by employing the magnetometric technique based on anomalous Hall measurements and confirm its intrinsic nature. In addition, on the basis of the thickness dependences of the anisotropy field, we identify the interfacial and bulk contributions. Furthermore, we demonstrate that the interfacial anisotropy in Fe3GeTe2-based heterostructures is locally controlled by adjacent layers, leading to the realization of multiple magnetic behaviors in a single channel. This work proposes that the magnetometric technique is a useful platform for investigating the intrinsic properties of vdW magnets and that functional devices can be realized by local interface engineering.

Dzyaloshinskii–Moriya interaction (DMI) plays a key role in the formation and stability of chiral magnetic objects, such as skyrmions and chiral domain-walls (DWs), which are used as building blocks of emerging high-density and high-speed devices. Here, we demonstrate that the DMI determines also the roughness of chiral DWs. Such DMI-dependent chiral roughness was observed from magnetic multilayer films of the Pt/Co/Pt heterostructure. Despite the stochastic nature of the DW roughness, the films clearly showed the roughness variation with respect to the DW chirality in balance with the DMI. The present analysis of the DW roughness offers a way to quantitatively determine the DMI-induced effective field as an essential parameter for the stability and dynamic characteristics of chiral DWs.

Herein, we propose an experimental scheme to determine the strength of the Heisenberg exchange interaction in ultrathin magnetic films. In this scheme, the chirality transition between the Bloch- and Néel-type domain walls is analyzed under an in-plane magnetic field. Subsequently, the exchange stiffness constant is estimated based on the strength of the magnetic field for chirality transitions, as proposed by an analytical theory pertaining to chirality transitions, and confirmed based on micromagnetic prediction. Using the magneto-optical Kerr effect with high sensitivity on surface atomic layers, the present scheme is applicable to ultrathin magnetic films down to a few atomic layers, whose sensitivity is well below the lowest sensitivity limit of conventional measurement schemes. Hence, the present scheme is useful for extending the experimental range to investigate the exchange stiffness of few-atomic-layer-thick magnetic films.

Antiferromagnetic materials are outstanding candidates for next generation spintronic applications, because their ultrafast spin dynamics makes it possible to realize several orders of magnitude higher-speed devices than conventional ferromagnetic materials1. Though spin-transfer torque (STT) is a key for electrical control of spins as successfully demonstrated in ferromagnetic spintronics, experimental understanding of STT in antiferromagnets has been still lacking despite a number of pertinent theoretical studies2-5. Here, we report experimental results on the effects of STT on domain-wall (DW) motion in antiferromagnetically-coupled ferrimagnets. We find that non-adiabatic STT acts like a staggered magnetic field and thus can drive DWs effectively. Moreover, the non-adiabaticity parameter {\beta} of STT is found to be significantly larger than the Gilbert damping parameter {\alpha}, challenging our conventional understanding of the non-adiabatic STT based on ferromagnets as well as leading to fast current-induced antiferromagnetic DW motion. Our study will lead to further vigorous exploration of STT for antiferromagnetic spin textures for fundamental physics on spin-charge interaction as wells for efficient electrical control of antiferromagnetic devices., Comment: 19 pages, 4 figures

Symmetry breaking is a fundamental concept that prevails in many branches of physics1–5. In magnetic materials, broken inversion symmetry induces the Dzyaloshinskii–Moriya interaction (DMI), which results in fascinating physical behaviours6–14 with the potential for application in future spintronic devices15–17. Here, we report the observation of a bulk DMI in GdFeCo amorphous ferrimagnets. The DMI is found to increase linearly with an increasing thickness of the ferrimagnetic layer, which is a clear signature of the bulk nature of DMI. We also found that the DMI is independent of the interface between the heavy metal and ferrimagnetic layer. This bulk DMI is attributed to an asymmetric distribution of the elemental content in the GdFeCo layer, with spatial inversion symmetry broken throughout the layer. We expect that our experimental identification of a bulk DMI will open up additional possibilities to exploit this interaction in a wide range of materials. A composition gradient is found to provide the necessary structural inversion asymmetry for a bulk Dzyaloshinskii–Moriya interaction to manifest itself.

Recently, magnetic multilayer systems have received again a great attention owing to their suitability for the generation of magnetic chiral spin structure. In this study, we experimentally investigated the interfacial Dzyaloshisnkii-Moriaya interaction (DMI) and the spin-Hall angle (SHA) of magnetic Co/Gd/Pt multilayers with respect to the repetition number $N$ of the multilayers. The DMI and SHA are important variables that govern the stability and mobility of a homochiral spin structure, respectively. The experimental results show that the ratio between the DMI and the dipole energy from the domain wall gradually decreases as $N$ increases, which is expected to be hard to achieve homochiral spin structure for larger $N$ and the values of SHA remain constant irrespective of $N$. The observed SHA invariance indicates that the Pt layers in repetition have a negligible effect on the SHA.

We theoretically study a ferrimagnetic domain-wall motion driven by a rotating magnetic field. We find that, depending on the magnitude and the frequency of the rotating field, the dynamics of a ferrimagnetic domain wall can be classified into two regimes. First, when the frequency is lower than a certain critical frequency set by the field magnitude, there is a stationary solution for the domain-wall dynamics, where a domain-wall in-plane magnetization rotates in-phase with the external field. The field-induced precession of the domain wall gives rise to the translational motion of the domain wall via the gyrotropic coupling between the domain-wall angle and position. In this so-called phase-locking regime, a domain-wall velocity increases as the frequency increases. Second, when the frequency exceeds the critical frequency, a domain-wall angle precession is not synchronous with the applied field. In this phase-unlocking regime, a domain wall velocity decreases as the frequency increases. Moreover, the direction of the domain-wall motion is found to be reversed across the angular compensation point where the net spin density of the ferrimagnet changes its sign. Our work suggests that the dynamics of magnetic solitons under time-varying biases may serve as platform to study critical phenomena., Comment: 7 pages, 1 table, 3 figures

Most of the existing research on the dynamics of magnetic solitons such as a domain wall (DW) has focused on the effect of DC forces, where the induced velocity is determined by the force strength. Here we show that AC forces such as an oscillating magnetic field or current are also able to move a DW straight via synchronization between the DW angle and the phase of the AC force. The resulting DW velocity is solely proportional to the driving frequency of the AC force, but the strength of the AC field just affects the frequency range for criteria for the phase-locking behavior. The AC-force-driven DW motion is shown to exhibit a phase locking-unlocking transition, a critical phenomenon akin to the Walker breakdown of a DC-bias-driven DW motion. Our work shows that a DW can be driven straight by synchronizing its angle to AC forces and thereby demonstrates a proof-of-concept of magnetic soliton rectifiers (i.e., DC motion induced by AC forces), shedding a light on the hitherto overlooked utility of internal degree of freedom for driving magnetic textures.

The magnetic exchange interaction is one of the key factors governing the basic characteristics of magnetic systems. In contrast to the symmetric nature of the Heisenberg exchange interaction, the interfacial Dzyaloshinskii-Moriya interaction (DMI) generates an antisymmetric exchange interaction, which offers challenging opportunities in spintronics with intriguing antisymmetric phenomena. The role of the DMI, however, is still under debate, because largely distinct strengths of the DMI have been measured for different magnetic objects, particularly chiral magnetic domain walls (DWs) and nonreciprocal spin waves (SWs). In this paper, by carefully examining the measurement principles, we demonstrate that both the DWs and SWs experience the same strength of the DMI. The key factor in this demonstration is to identify the appropriate experimental conditions by excluding all possible artifacts that causes additional undesired symmetric and antisymmetric contributions in chiral DW dynamics. The present demonstration, therefore, verifies the universality of the DMI between different magnetic dynamics as an intrinsic exchange interaction and also, guarantees the compatibility of several DMI-measurement schemes recently proposed.

Antiferromagnetic spintronics is an emerging research field which aims to utilize antiferromagnets as core elements in spintronic devices. A central motivation toward this direction is that antiferromagnetic spin dynamics is expected to be much faster than ferromagnetic counterpart because antiferromagnets have higher resonance frequencies than ferromagnets. Recent theories indeed predicted faster dynamics of antiferromagnetic domain walls (DWs) than ferromagnetic DWs. However, experimental investigations of antiferromagnetic spin dynamics have remained unexplored mainly because of the immunity of antiferromagnets to magnetic fields. Furthermore, this immunity makes field-driven antiferromagnetic DW motion impossible despite rich physics of field-driven DW dynamics as proven in ferromagnetic DW studies. Here we show that fast field-driven antiferromagnetic spin dynamics is realized in ferrimagnets at the angular momentum compensation point TA. Using rare-earth 3d-transition metal ferrimagnetic compounds where net magnetic moment is nonzero at TA, the field-driven DW mobility remarkably enhances up to 20 km/sT. The collective coordinate approach generalized for ferrimagnets and atomistic spin model simulations show that this remarkable enhancement is a consequence of antiferromagnetic spin dynamics at TA. Our finding allows us to investigate the physics of antiferromagnetic spin dynamics and highlights the importance of tuning of the angular momentum compensation point of ferrimagnets, which could be a key towards ferrimagnetic spintronics.

Charged particles exhibit the Hall effect in the presence of magnetic fields. Analogously, ferromagnetic skyrmions with non-zero topological charges and finite fictitious magnetic fields exhibit the skyrmion Hall effect, which is detrimental for applications. The skyrmion Hall effect has been theoretically predicted to vanish for antiferromagnetic skyrmions because the fictitious magnetic field, proportional to net spin density, is zero. We experimentally confirm this prediction by observing current-driven transverse elongation of pinned ferrimagnetic bubbles. Remarkably, the skyrmion Hall effect, estimated with the angle between the current and bubble elongation directions, vanishes at the angular momentum compensation temperature where the net spin density vanishes. This study establishes a direct connection between the fictitious magnetic field and spin density, offering a pathway towards the realization of skyrmionic devices., 14 pages, 4 figures

Chirality causes diverse phenomena in nature such as the formation of biological molecules, antimatters, non-collinear spin structures, and magnetic skyrmions. The chirality in magnetic materials is often caused by the noncollinear exchange interaction, called the Dzyaloshinskii-Moriya interaction (DMI). The DMI produces topological spin alignments such as the magnetic skyrmions and chiral domain walls (DWs). In the chiral DWs, the DMI generates an effective magnetic field $H_{DMI}$, resulting in a peculiar DW speed variation in the DW creep regime. However, the role of $H_{DMI}$ over the different DW-dynamics regimes remains elusive, particularly due to recent observation of distinct behaviors between the creep and flow regimes. We hereby demonstrate experimentally that the role of $H_{DMI}$ is invariant over the creep and flow regimes. In the experiments, the pure DMI effect is quantified by decomposing the symmetric and antisymmetric contributions of the DW motion. The results manifest that the antisymmetric contribution vanishes gradually across the creep and flow regimes, revealing that the symmetric contribution from $H_{DMI}$ is unchanged. Though the DW dynamics is governed by distinct mechanisms, the present observation demonstrates the uniqueness of the DMI effect on the DWs over the creep and flow regimes., 19 pages, 4 figures

The spin-transfer-torque-driven (STT-driven) dynamics of a domain wall in an easy-axis rare-earth transition-metal ferrimagnet is investigated theoretically and numerically in the vicinity of the angular momentum compensation point $T_A$, where the net spin density vanishes. The particular focus is given on the unusual interaction of the antiferromagnetic dynamics of a ferrimagnetic domain wall and the adiabatic component of STT, which is absent in antiferromagnets but exists in the ferrimagnets due to the dominant coupling of conduction electrons to transition-metal spins. Specifically, we first show that the STT-induced domain-wall velocity changes its sign across $T_A$ due to the sign change of the net spin density, giving rise to a phenomenon unique to ferrimagnets that can be used to characterize $T_A$ electrically. It is also shown that the frequency of the STT-induced domain-wall precession exhibits its maximum at $T_A$ and it can approach the spin-wave gap at sufficiently high currents. Lastly, we report a numerical observation that, as the current density increases, the domain-wall velocity starts to deviate from the linear-response result, calling for a more comprehensive theory for the domain-wall dynamics in ferrimagnets driven by a strong current., Comment: 8 pages, 5 figures

This study introduced food waste into re-vegetation base materials for surface loss recovery of carry-away highway cut slope. The object of this study is to derive the mixing ratio of food waste by conducting a test installation, monitoring, analysis and evaluation for recovery of carry-away highway cut slope. The following items were investigated and analyzed each experimental zone to draw mixing ratio of re-vegetation base materials and food waste : the physical and chemical properties of the vegetation base materials, soil-hardness, soil-humidity, left out and the collapsed point, established number of trees, species richness of grass species and tree species, coverage, pest status, and invasion of disturbance species. The re-vegetation method was evaluated by each experiment zone which has different mixing ratio. As a result, experiment zone A was rated 45 points out of 60 rating points as the best re-vegetation method. However, this study result has been derived from one construction and short-term monitoring. In order to derive the suitable and dependable mixing ratio, conducting an objective re-vegetation method evaluation and long-term experiment and monitoring is required.

Spin-related phenomena, such as the giant magnetoresistance and the spin-transfer torque, have led to a new era of nano-spintronics in last two decades. The discovery of these physical phenomena has contributed to a substantial increase in the data storage capacity of computers. Another revolutionary phenomenon, the interfacial Dzyaloshinskii-Moriya interaction (DMI), was recently discovered in ultra-thin ferromagnet/heavy-metal bilayers. The DMI stabilizes nanometre-sized chiral spin textures such as Neel domain walls and hedgehog skyrmions. These chiral objects find the potential for applications in ultra-high density, low-energy, and high-speed memory devices because they are stable due to topological protection and easy to move with high efficiency. As both stability and current-driven speed of chiral spin textures are proportional to the DMI strength [A. Thiaville et al., Europhys Lett. 100, 57002 (2012); A. Fert, V. Cros, and J. Sampiao, Nat. Nanotechnol. 8, 152 (2013)], tremendous efforts are being devoted to finding high-DMI materials. In this respect, understanding the microscopic origin of DMI is of critical importance. Here we discuss the microscopic origin of the interfacial DMI with experimental and theoretical studies as follows: First, we show the temperature dependence of the DMI for a Pt/Co/MgO trilayer; the DMI increases with decreasing temperature in a range from 300 to 100 K. To discuss this temperature dependence of the DMI, that of the spin and orbital magnetic moments of Co and Pt is studied by X-ray magnetic circular dichroism (XMCD) spectroscopy. We find that spin moment values of Co and Pt show temperature dependences due to change in Heisenberg exchange. Furthermore, the intra-atomic magnetic dipole moment, which is due to the asymmetric spin-density distribution, shows strong temperature dependence, suggesting a sizable modification of the charge distribution between the in-plane and the out-of-plane d-orbitals under temperature variation. We also find that the out-of-plane orbital moment shows large temperature dependence while in-plane orbital moment does not, revealing a close connection between the anisotropy of orbital moment and the DMI. The ab-initio and the tight-binding model calculations suggest that the ISB-dependent electron hopping, which gives rise to the asymmetric charge distribution at the interface of the FM/HM, is a possible microscopic origin of the correlation between the orbital anisotropy and the DMI.

Determining the angular momentum compensation temperature of ferrimagnets is an important step towards ferrimagnetic spintronics, but is not generally easy to achieve it experimentally. We propose a way to estimate the angular momentum compensation temperature of ferrimagnets. We find a linear relation between the compensation temperatures of the magnetization and angular momentum in GdFeCo ferrimagnetic materials, which is proved by theoretically as well as experimentally. The linearity comes from the power-law criticality and is governed by the Curie temperature and the Land\'e g factors of the elements composing the ferrimagnets. Therefore, measuring the magnetization compensation temperature and the Curie temperature, which are easily assessable experimentally, enables to estimate the angular momentum compensation temperature of ferrimagnets. Our study provides efficient avenues into an exciting world of ferrimagnetic spintronics., Comment: 18 pages, 4 figures

Chiral spin textures of a ferromagnetic layer in contact to a heavy non-magnetic metal, such as Néel-type domain walls and skyrmions, have been studied intensively because of their potential for future nanomagnetic devices. The Dyzaloshinskii–Moriya interaction (DMI) is an essential phenomenon for the formation of such chiral spin textures. In spite of recent theoretical progress aiming at understanding the microscopic origin of the DMI, an experimental investigation unravelling the physics at stake is still required. Here we experimentally demonstrate the close correlation of the DMI with the anisotropy of the orbital magnetic moment and with the magnetic dipole moment of the ferromagnetic metal in addition to Heisenberg exchange. The density functional theory and the tight-binding model calculations reveal that inversion symmetry breaking with spin–orbit coupling gives rise to the orbital-related correlation. Our study provides the experimental connection between the orbital physics and the spin–orbit-related phenomena, such as DMI., 原子磁石どうしが捻れて並ぶ現象のミクロな起源を解明 --新原理の情報記録技術をめざして--. 京都大学プレスリリース. 2018-05-01.

We investigate the effect of the Dzyaloshinskii Moriya interaction (DMI) on magnetic domain nucleation in a ferromagnetic thin film with perpendicular magnetic anisotropy. We propose an extended droplet model to determine the nucleation field as a function of the in-plane field. The model can explain the experimentally observed nucleation in a CoNi microstrip with the interfacial DMI. The results are also reproduced by micromagnetic simulation based on the string model. The electrical measurement method proposed in this study can be widely used to quantitatively determine the DMI energy density.

Dzyaloshinskii-Moriya interaction (DMI) in magnetic objects is of enormous interest, because it generates a built-in chirality of magnetic domain walls (DWs) and topologically-protected skyrmions for efficient motion driven by spin-orbit torques. Because of its importance for perspective applications and academic curiosities, many experimental efforts have been devoted to DMI investigation. However, current experimental probing techniques cover only limited ranges of the DMI with specific sample requirements, and there are no versatile techniques covering a wide range of DMI. Here, we present a unique experimental scheme to quantify DMI over a wide range based on the angular dependence of asymmetric DW motion. It can determine DMI even larger than the maximum magnetic field strength, demonstrating that various strengths of DMI can be quantified using a single measurement setup. This scheme provides a standard technique over a wide range of DMI, which is essential to DMI-related emerging fields in nanotechnology., Comment: 17 pages, 4 figures

Broken symmetries in diverse systems generate a number of intriguing phenomena and the analysis on such broken symmetries often provides decisive clues for exploring underlying physics in the systems. Recently, in magnetic thin-film systems, the Dzyaloshinskii-Moriya interaction (DMI)---induced by the broken symmetry of structural inversion---accounts for various chiral phenomena, which are of timely issues in spintronics. Here, we report an experimental observation on unexpected tilting of magnetic domain walls (DWs) due to the broken symmetry under the application of the magnetic field transverse to the magnetic wire systems. It has been predicted that the DMI possibly causes such DW tilting in the direction of the energy minimization. However, very interestingly, experimental observation reveals that the DW tilting does not follow the prediction based on the energy minimization, even for the tilting direction. Instead, the DW tilting is governed by the DW speed asymmetry that is initiated by the DW pinning at wire edges. A simple analytic model is proposed in consideration of the DW speed asymmetry at wire edges, which successfully explains the experimental observation of the DW tilting directions and angles, as confirmed by numerical simulation. The present study manifests the decisive role of the DW pinning with the DW speed asymmetry, which determines the DW configuration and consequently, the dynamics.

Kaloula borealis is the species of Amphibia which belongs to Kaloula genus and it is the only species inhabiting in Korea. The population size and habitat of Kaloula borealis have been significantly decreased on a national scale due to the diversified developments and the uses of agricultural pesticides. Accordingly, the Ministry of Environment has designated and managed them as the class II of endangered species, in accordance with ?Endangered Species Protection and Management Act?; however, a particular study focused on the ecological restoration of Kaloula borealis is desperately needed to prevent their extinction. This study was conducted to propose the HSI (Habit Suitability Index) of Kaloula borealis based on literature survey on ecology and habitats of Kaloula borealis, as well as their HSI. Factors to be investigated in HSI include: space, feed, cover, water(breeding) and threatening factors and the variables of each factor were also proposed. The distance from wetland, grassland, farm, stream and rice paddy, as well as the altitude of spawning pond were proposed as the variables of space, whereas the bed structure of forest and low-rise grassland were proposed as the variables of feeding. The variables of water (breeding) include the area of permanent and temporary wetlands, coverage of emerged pants (ratio of open water), water depth, water temperature, water quality, pH level, etc., whereas the presence of predator, distance from street and pollutants were proposed as the variables of threatening factor. The sub-standards by HSI factor of Kaloula borealis have been drawn from in-depth consultation with experts and based on this, the final HSI of Kaloula borealis was developed.

We propose here a method for compensating the Joule-heating effects in the current-induced domain wall motion (CIDWM). In CIDWM experiments, the current induces not only the spin-transfer torque (STT) effects but also the Joule-heating effects, and both effects influence the domain wall (DW) motion. It is thus desired to develop a way to compensate the Joule-heating effects, in order to determine the pure STT effects on the DW motion. Up to now, in studies of DW creeping motions, such Joule-heating effects have been eliminated based on the Arrhenius law by assuming the temperature-independent creep scaling constants. However, here we find that such scaling constants are sensitive to the temperature, from the DW creeping experiment in Pt/Co/Pt wires with temperature control in a cryostat. By accounting the temperature dependence of the scaling constants, we demonstrate that all the DW speeds with various temperatures are exactly collapsed onto a single universal curve, which enables us to examine the pure STT effects on the DW motion.

The one-dimensional magnetic skyrmion motion induced by an electric current has attracted much interest because of its application potential in next-generation magnetic memory devices. Recently, the unidirectional motion of large (20 μm in diameter) magnetic bubbles with two-dimensional skyrmion topology, driven by an oscillating magnetic field, has also been demonstrated. For application in high-density memory devices, it is preferable to reduce the size of skyrmion. Here we show by numerical simulation that a skyrmion of a few tens of nanometres can also be driven by high-frequency field oscillations, but with a different direction of motion from the in-plane component of the tilted oscillating field. We found that a high-frequency field for small skyrmions can excite skyrmion resonant modes and that a combination of different modes results in a final skyrmion motion with a helical trajectory. Because this helical motion depends on the frequency of the field, we can control both the speed and the direction of the skyrmion motion, which is a distinguishable characteristic compared with other methods.

The domain-wall (DW) motion of ferrimagnets is investigated with respect to the angular-momentum-compensation temperature T A for a wide range of magnetic fields μ0 H z , ranging from the depinning to flow regimes. While the DW velocity v exhibits a maximum at T A in the flow regime regardless of μ0 H z , the temperature at which v is maximized depends on μ0 H z because of the temperature dependence of the depinning field μ0 H dep, causing difficulty in determining T A. To solve this problem, we propose a reduced coordinate μ0 H z − μ0 H dep, which reveals that v is maximized at T A even in the depinning regime. Our work suggests that μ0 H dep should be identified prior to determining T A.

We report the experimental observation of distinct stochasticities between domain-wall motions driven by either a magnetic field or an electric current. In Pt/Co/Ta trilayer films, the arrival time of the current-induced domain-wall motion has a much broader dispersion compared to that of the field-induced motion. Images of the magneto-optical Kerr effect microscope reveal that the current-induced motion experiences significantly stronger domain-wall pinning, contrary to the field-induced domain-wall motion, even though both types of motion take place in the same area of the film. Consequently, the former exhibits stepwise propagation in time, whereas the behavior of the latter is smooth and monotonic. A simple analytic model based on depinning statistics is proposed to explain the relationship between the wide dispersion and the strong pinning mechanisms in current-induced domain-wall motion.

The influence of temperature on the magnetic-field-driven domain wall (DW) motion is investigated in GdFeCo ferrimagnets with perpendicular magnetic anisotropy (PMA). We find that the depinning field strongly depends on temperature. Moreover, it is also found that the saturation magnetization exhibits a similar dependence on temperature to that of depinning field. From the creep-scaling criticality, a simple relation between the depinning field and the properties of PMA is clearly identified theoretically as well as experimentally. Our findings open a way for a better understanding how the magnetic properties influence on the depinning field in magnetic system and would be valuably extended to depinning studies in other system., Comment: 18 pages,5 figures

We propose an alternative method of determining the magnetic anisotropy field μ0 H K in ferro-/ferrimagnets. On the basis of the droplet nucleation model, there exists linearity between domain-wall (DW) energy density and in-plane magnetic field. We find that the slope is simply represented by μ0 H K and Dzyaloshinskii–Moriya interaction (DMI). By measuring the in-plane magnetic field dependence of the coercivity field, closely corresponding to the DW energy density, a robust value for μ0 H K can be quantified. This robust value can be used to determine μ0 H K over a wide range of values, overcoming the limitations caused by the small strength of the external magnetic field typically used in experiments.

In this study, we investigate the influence of the ferromagnetic layer thickness on the magnetization process. A series of ultrathin Pt/Co/TiO2/Pt films exhibits domain-wall (DW) speed variation of over 100,000 times even under the same magnetic field, depending on the ferromagnetic layer thickness. From the creep-scaling analysis, such significant variation is found to be mainly attributable to the thickness-dependence of the creep-scaling constant in accordance with the creep-scaling theory of the linear proportionality between the creep-scaling constant and the ferromagnetic layer thickness. Therefore, a thinner film shows a faster DW speed. The DW roughness also exhibits sensitive dependence on the ferromagnetic layer thickness: a thinner film shows smoother DW. The present observation provided a guide for an optimal design rule of the ferromagnetic layer thickness for better performance of DW-based devices.

Ferromagnetic resonance (FMR) measurement is an important experimental technique for the study of magnetic dynamics. We designed and set up the vector network analyzer ferromagnetic resonance (VNA-FMR) measurement system with home made coplanar waveguides (CPW). We examined 10-, 20-, 40-nm thick Py thin films to test the performance of the VNA-FMR measurement system. We measured S-parameter (transmission/reflection coefficient) of Py thin films on a CPW. Resonance frequency is investigated from 2.5 to 7 GHz for a field range from 0 to 490 Oe. The VNA-FMR data shows the resonance frequency increment when the external magnetic field increases. We also investigated Gilbert damping constant of Py thin film using resonance frequency () and linewidth (). After investigating dependence of thickness, we find that an decrease in S-parameter intensity as Py thin film thickness decreases. And the FMR results show that the effective saturation magnetization, , increase from 7.205(0.013) kOe to 7.840(0.014) kOe, while the film thickness varies from 10 to 40 nm.

In chiral magnetic materials, numerous intriguing phenomena such as built-in chiral magnetic domain walls (DWs) and skyrmions are generated by the Dzyaloshinskii–Moriya interaction (DMI). The DMI also results in asymmetric DW speeds under an in-plane magnetic field, which provides a useful scheme to measure the strength of the DMI. However, recent findings of additional asymmetries such as chiral damping have inhibited the unambiguous determination of the DMI strength, and the underlying mechanism of overall asymmetries comes under debate. Here, we experimentally investigate the nature of the additional asymmetry by extracting the DMI-induced symmetric contribution from the DW speed. Our results reveal that the additional asymmetry has a truly antisymmetric nature with the typical behavior governed by the DW chirality. In addition, the antisymmetric contribution alters the DW speed by a factor of 100, dominating the overall variation in DW speed. Thus, experimental inaccuracies can be largely removed by calibration with such antisymmetric contributions, enabling the standard DMI measurement scheme. Fast-moving domain walls separating regions with spin-up or spin-down states are desirable for high-performance spintronic memory and logic devices. The Dzyaloshinskii–Moriya interaction gives rise to an asymmetric distribution of domain wall speeds in chiral magnetic materials, providing a convenient way to determine the strength of the interaction. However, the recent discovery of additional asymmetries has complicated the analysis of measurements. Now, Sug-Bong Choe from Seoul National University and co-workers have experimentally determined the chiral nature of the additional symmetry for the first time. This contribution, which could arise from either a form of energy dissipation called chiral damping or from natural variations in domain wall widths, can alter domain wall speeds by a factor of 100. Chiral magnetic domain-wall (DW) speed variation is investigated. We demonstrate that the symmetric contribution in the DW speed attributes to the chiral DW energy density. Next, by deducing this symmetric contribution, the additional asymmetry was extracted. The extracted additional asymmetry exhibits truly antisymmetric nature and is governed by DW chirality. Moreover, this antisymmetry (additional asymmetry) changes overall DW speed more than a factor of 100 to the extent of dominating the symmetric contribution. These findings not only provide the artifact-free Dyzaloshinskii–Moriya interaction measurement scheme, but also contribute to the investigation of the origin of the additional asymmetry.

In this study, a MOKE (Magneto-optical Kerr effect) measurement method for magnetic nanostructures is proposed. Theoretically, the MOKE signal enhancement can be predicted and confirmed when an anti-reflection coated substrate is used. Since MOKE is a ratio of reflectivity and the difference between the reflectivities for two magnetic states, when the reflectivity of the substrate part is reduced by employing an anti-reflection coated substrate, MOKE signal enhancement can be achieved. The enhancement is confirmed by simple numerical MOKE calculations. When the reflectivity of an anti-reflection coated substrate is 0.7%, the calculated MOKE signal is about 79% of its bulk values for the 100-nm wide Fe nanowire with a 1500-nm radius laser beam. It was found that, for various numerical calculations, a larger MOKE signal is obtained relative to a smaller substrate reflectivity.

Unidirectional motion of magnetic domain walls is the key concept underlying next-generation domain-wall-mediated memory and logic devices. Such motion has been achieved either by injecting large electric currents into nanowires or by employing domain-wall tension induced by sophisticated structural modulation. Herein, we demonstrate a new scheme without any current injection or structural modulation. This scheme utilizes the recently discovered chiral domain walls, which exhibit asymmetry in their speed with respect to magnetic fields. Because of this asymmetry, an alternating magnetic field results in the coherent motion of the domain walls in one direction. Such coherent unidirectional motion is achieved even for an array of magnetic bubble domains, enabling the design of a new device prototype—magnetic bubblecade memory—with two-dimensional data-storage capability.

A mercury film (MF) is prepared by an electrochemical deposition on a glassy carbon electrode (GCE), and employed for an analysis of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) using square-wave stripping voltammetry (SWSV). RDX was deposited at −0.15 V (vs. Ag/AgCl) for 120 s, then reduced at −0.7 V on the MF coated GCE(MFGCE). Optimal experimental conditions were searched and reported for the analysis. Two linear concentration ranges were observed: one in a lower RDX concentration range of 0.2–10 mg l −1 and the other in a higher RDX concentration range of 10.0–100.0 mg l −1 with a 120 s of pre-concentration time. At RDX concentrations of 2 and 8 mg l −1 , the relative standard deviations in measured concentrations ( n =16) were 9.79 and 0.49%, respectively. The detection limit found to be 0.12 mg l −1 with the 120 s accumulation time. The method was applied to determine RDX in several soil samples that yielded a relative error of 1% in the concentrations.

Harmonic Hall measurements were performed in Pt/GdFeCo bilayers to quantify the effective field resulting from the spin-orbit torque at various temperatures, both above and below the magnetization compensation temperature (TM). We found that the damping-like torque rapidly increased near the TM of the GdFeCo, which was attributed to a reduction in the net magnetic moment. Moreover, most importantly, the resulting spin Hall efficiency turned out to be constant across the temperature range.

The coherent unidirectional motion of magnetic domain walls (DWs) is a key technology used in memory and logic device applications, as demonstrated in magnetic strips by electric current flow as well as in films by oscillation of a tilted magnetic field. Here we introduce a coherent unidirectional motion of DWs in the strip, utilizing an oscillating field, which is described within a previous 1D model. The essential criterion for DW motion in this approach is the oscillating-field-induced modulation of the DW width, which has not been previously considered. This DW motion driven by width modulation sheds light on high frequency domain manipulation in spin devices. A comprehensive inspection of field angle dependence reveals that unidirectional DW motion in this model requires chiral DWs, followed by asymmetric deformation of the domain shape.

Unidirectional motion of magnetic domain walls is the key concept underlying next-generation domain-wall-mediated memory and logic devices. Such motion has been achieved either by injecting large electric currents into nanowires or by employing domain-wall tension induced by sophisticated structural modulation. Herein, we demonstrate a new scheme without any current injection or structural modulation. This scheme utilizes the recently discovered chiral domain walls, which exhibit asymmetry in their speed with respect to magnetic fields. Because of this asymmetry, an alternating magnetic field results in the coherent motion of the domain walls in one direction. Such coherent unidirectional motion is achieved even for an array of magnetic bubble domains, enabling the design of a new device prototype-magnetic bubblecade memory-with two-dimensional data-storage capability., Comment: 16 pages, 5 figures, ver.2: 2 supplementary movies