Showing papers on "Magnetic domain published in 2016"
TL;DR: This work designed cobalt-based multilayered thin thin metals in which the cobalt layer is sandwiched between two heavy metals and so provides additive interfacial Dzyaloshinskii-Moriya interactions (DMIs), which reach a value close to 2 mJ m(-2) in the case of the Ir|Co|Pt asymmetric multilayers.
Abstract: Facing the ever-growing demand for data storage will most probably require a new paradigm. Nanoscale magnetic skyrmions are anticipated to solve this issue as they are arguably the smallest spin textures in magnetic thin films in nature. We designed cobalt-based multilayered thin films in which the cobalt layer is sandwiched between two heavy metals and so provides additive interfacial Dzyaloshinskii-Moriya interactions (DMIs), which reach a value close to 2 mJ m(-2) in the case of the Ir|Co|Pt asymmetric multilayers. Using a magnetization-sensitive scanning X-ray transmission microscopy technique, we imaged small magnetic domains at very low fields in these multilayers. The study of their behaviour in a perpendicular magnetic field allows us to conclude that they are actually magnetic skyrmions stabilized by the large DMI. This discovery of stable sub-100 nm individual skyrmions at room temperature in a technologically relevant material opens the way for device applications in the near future.
1,023 citations
TL;DR: This Letter presents the experimental observation and micromagnetic simulations of spin-wave propagation inside nano-sized domain walls and realizes a first step towards a reconfigurable domain-wall-based magnonic nanocircuitry.
Abstract: Magnetic domain walls in a permalloy sample can be arranged to define waveguides for the transmission of information via magnons. In the research field of magnonics1,2,3,4,5,6,7, it is envisaged that spin waves will be used as information carriers, promoting operation based on their wave properties. However, the field still faces major challenges. To become fully competitive, novel schemes for energy-efficient control of spin-wave propagation in two dimensions have to be realized on much smaller length scales than used before. In this Letter, we address these challenges with the experimental realization of a novel approach to guide spin waves in reconfigurable, nano-sized magnonic waveguides. For this purpose, we make use of two inherent characteristics of magnetism: the non-volatility of magnetic remanence states and the nanometre dimensions of domain walls formed within these magnetic configurations. We present the experimental observation and micromagnetic simulations of spin-wave propagation inside nano-sized domain walls and realize a first step towards a reconfigurable domain-wall-based magnonic nanocircuitry.
256 citations
TL;DR: The first experimental achievement of a multilevel memristor compatible with spin-torque magnetic random access memories is shown and it is demonstrated that the magnetic synapse has a large number of intermediate resistance states, sufficient for neural computation.
Abstract: Memristors are non-volatile nano-resistors which resistance can be tuned by applied currents or voltages and set to a large number of levels. Thanks to these properties, memristors are ideal building blocks for a number of applications such as multilevel non-volatile memories and artificial nano-synapses, which are the focus of this work. A key point towards the development of large scale memristive neuromorphic hardware is to build these neural networks with a memristor technology compatible with the best candidates for the future mainstream non-volatile memories. Here we show the first experimental achievement of a multilevel memristor compatible with spin-torque magnetic random access memories. The resistive switching in our spin-torque memristor is linked to the displacement of a magnetic domain wall by spin-torques in a perpendicularly magnetized magnetic tunnel junction. We demonstrate that our magnetic synapse has a large number of intermediate resistance states, sufficient for neural computation. Moreover, we show that engineering the device geometry allows leveraging the most efficient spin torque to displace the magnetic domain wall at low current densities and thus to minimize the energy cost of our memristor. Our results pave the way for spin-torque based analog magnetic neural computation.
198 citations
Journal Article•
142 citations
TL;DR: The present approach can guide the systematic tuning of the magnetic easy axis and coercivity in the desired direction with respect to crystal orientation in the nanoscale regime and can be achieved on virtually any type of substrate.
Abstract: Perpendicular magnetization and precise control over the magnetic easy axis in magnetic thin film is necessary for a variety of applications, particularly in magnetic recording media. A strong (111) orientation is successfully achieved in the CoFe2O4 (CFO) thin film at relatively low substrate temperature of 100 °C, whereas the (311)-preferred randomly oriented CFO is prepared at room temperature by the DC magnetron sputtering technique. The oxygen-deficient porous CFO film after post-annealing gives rise to compressive strain perpendicular to the film surface, which induces large perpendicular coercivity. We observe the coercivity of 11.3 kOe in the 40-nm CFO thin film, which is the highest perpendicular coercivity ever achieved on an amorphous SiO2/Si substrate. The present approach can guide the systematic tuning of the magnetic easy axis and coercivity in the desired direction with respect to crystal orientation in the nanoscale regime. Importantly, this can be achieved on virtually any type of substrate.
141 citations
TL;DR: In this paper, the authors evaluate the actual applicability of the discussed materials for use as pole tips in electromagnets, in particular in nanoscale magnetic hard disk drive read-write heads; the technological advancement of the latter has been a very strong driving force in the development of nanomagnetism.
Abstract: The creation of large magnetic fields is a necessary component in many technologies, ranging from magnetic resonance imaging, electric motors and generators, and magnetic hard disk drives in information storage. This is typically done by inserting a ferromagnetic pole piece with a large magnetisation density MS in a solenoid. In addition to large MS, it is usually required or desired that the ferromagnet is magnetically soft and has a Curie temperature well above the operating temperature of the device. A variety of ferromagnetic materials are currently in use, ranging from FeCo alloys in, for example, hard disk drives, to rare earth metals operating at cryogenic temperatures in superconducting solenoids. These latter can exceed the limit on MS for transition metal alloys given by the Slater-Pauling curve. This article reviews different materials and concepts in use or proposed for technological applications that require a large MS, with an emphasis on nanoscale material systems, such as thin and ultra-thin films. Attention is also paid to other requirements or properties, such as the Curie temperature and magnetic softness. In a final summary, we evaluate the actual applicability of the discussed materials for use as pole tips in electromagnets, in particular, in nanoscale magnetic hard disk drive read-write heads; the technological advancement of the latter has been a very strong driving force in the development of the field of nanomagnetism.
134 citations
TL;DR: Topological defects such as magnetic solitons, vortices, Bloch lines, and skyrmions start to play an important role in modern magnetism due to their extraordinary stability as discussed by the authors.
Abstract: Topological defects such as magnetic solitons, vortices, Bloch lines, and skyrmions start to play an important role in modern magnetism due to their extraordinary stability which can be hailed as future memory devices.
122 citations
TL;DR: In this paper, the BaFe11.9In0.1O19 polycrystalline sample has been performed in a wide temperature range from 10 K up to 730 K and in the magnetic fields up to 14 T.
114 citations
TL;DR: In this article, the anisotropy of a nano-graphene sandwich-like structure has been abstracted based on the Ising model with the aisotropic anisotropic model.
112 citations
TL;DR: The SOT-assisted switching in heavy metal/magnetic insulator systems is reported and can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.
Abstract: As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.
100 citations
TL;DR: In this paper, the in-plane and out-of-plane magnetizations induced at the interface between the ferromagnetic insulator (FMI) EuS and the three-dimensional topological insulator Bi2Se3 were investigated.
Abstract: When a topological insulator (TI) is in contact with a ferromagnet, both time-reversal and inversion symmetries are broken at the interface An energy gap is formed at the TI surface, and its electrons gain a net magnetic moment through short-range exchange interactions Magnetic TIs can host various exotic quantum phenomena, such as massive Dirac fermions, Majorana fermions, the quantum anomalous Hall effect and chiral edge currents along the domain boundaries However, selective measurement of induced magnetism at the buried interface has remained a challenge Using magnetic second-harmonic generation, we directly probe both the in-plane and out-of-plane magnetizations induced at the interface between the ferromagnetic insulator (FMI) EuS and the three-dimensional TI Bi2Se3 Our findings not only allow characterizing magnetism at the TI-FMI interface but also lay the groundwork for imaging magnetic domains and domain boundaries at the magnetic TI surfaces
TL;DR: In this paper, magnetic force microscopy was used to observe the magnetic microstructure of Fe3GeTe2 at 4'K on the (001) surface, and the surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis.
Abstract: Magnetic force microscopy was used to observe the magnetic microstructure of Fe3GeTe2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width Ds = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization Ms = 376 emu/cm3 and the uniaxial magnetocrystalline anisotropy constant Ku = 1.46 × 107 erg/cm3), was used to determine the following micromagnetic parameters for Fe3GeTe2 from phenomenological models: the domain wall energy γw = 4.7 erg/cm2, the domain wall thickness δw = 2.5 nm, the exchange stiffness constant Aex = 0.95 × 10−7 erg/cm, the exchange length lex = 2.3 nm, and the critical single domain particle diameter dc = 470 nm.
TL;DR: In this article, the microscopic three-temperature model was used to describe AOS in a perpendicularly magnetized ferromagnetic Co/Pt system, and it was shown that AOS can be explained with the Inverse Faraday Effect (IFE).
Abstract: The microscopic mechanism behind the all optical switching (AOS) in ferromagnets has triggered intense scientific debate. Here, the microscopic three-temperature model is utilized to describe AOS in a perpendicularly magnetized ferromagnetic Co/Pt system. We demonstrate that AOS in such a ferromagnet can be explained with the Inverse Faraday Effect (IFE). The influence of the strength and lifetime of the IFE induced field pulse on the switching process are investigated. We found that because of strong spin-orbit coupling, the minimal lifetime of the IFE needed to obtain switching is of the order of 0.1 ps, which is shorter than previously assumed. Moreover, spatial images of the domain pattern after AOS in Co/Pt, as well as their dependence on applying an opposite magnetic field, are qualitatively reproduced.
TL;DR: In this paper, the authors present prototypes of a logic device that encodes information in the position of a magnetic domain wall in a ferromagnetic wire, which can be used to encode and propagate information.
Abstract: Spintronic computing promises superior energy efficiency and nonvolatility compared to conventional field-effect transistor logic. But, it has proven difficult to realize spintronic circuits with a versatile, scalable device design that is adaptable to emerging material physics. Here we present prototypes of a logic device that encode information in the position of a magnetic domain wall in a ferromagnetic wire. We show that a single three-terminal device can perform inverter and buffer operations. We demonstrate one device can drive two subsequent gates and logic propagation in a circuit of three inverters. This prototype demonstration shows that magnetic domain wall logic devices have the necessary characteristics for future computing, including nonlinearity, gain, cascadability, and room temperature operation. Ferromagnetic nanowires act as conduits for magnetic domain walls which may in principle be used to encode and propagate information. Here, the authors present current-based nanowire domain wall logic prototypes with operational properties required for real devices.
TL;DR: Simulations predict that the ultrafast motion of magnetic domain walls at velocities in a range above 1000 m s-1 can lead to the spontaneous excitation of spin waves in a process that is the magnetic analog of the Cherenkov effect.
Abstract: The dynamic properties of magnetic domain walls in nanotubes and in cylindrical nanowires can be significantly different from the well known domain wall dynamics in thin films and in flat thin strips. The main differences are the occurrence of chiral symmetry breaking and, perhaps more importantly, the possibility to obtain magnetic domain walls that are stable against the usual Walker breakdown. This stability enables the magnetic field-driven propagation of the domain walls in nanotubes and nanocylinders at constant velocities which are significantly higher than the usual propagation speeds of the domain walls. Simulations predict that the ultrafast motion of magnetic domain walls at velocities in a range above 1000 m s-1 can lead to the spontaneous excitation of spin waves in a process that is the magnetic analog of the Cherenkov effect. In the case of solid cylindrical wires, the domain wall can contain a micromagnetic point singularity. We discuss the current knowledge on the ultrafast dynamics of such Bloch points, which remains still largely unexplored.
TL;DR: In this paper, the influence of the film thickness (5 - 85 nm) on the sample magnetic properties was investigated in a wide composition range between 15 at% and 38 at.% of Tb.
Abstract: Ferrimagnetic rare earth - transition metal Tb-Fe alloy thin films exhibit a variety of different magnetic properties, which depends strongly on composition and temperature. In this study, first the influence of the film thickness (5 - 85 nm) on the sample magnetic properties was investigated in a wide composition range between 15 at.% and 38 at.% of Tb. From our results, we find that the compensation point, remanent magnetization, and magnetic anisotropy of the Tb-Fe films depend not only on the composition but also on the thickness of the magnetic film up to a critical thickness of about 20-30 nm. Beyond this critical thickness, only slight changes in magnetic properties are observed. This behavior can be attributed to a growth-induced modification of the microstructure of the amorphous films, which affects the short range order. As a result, a more collinear alignment of the distributed magnetic moments of Tb along the out-of-plane direction with film thickness is obtained. This increasing contribution of the Tb sublattice magnetization to the total sample magnetization is equivalent to a sample becoming richer in Tb and can be referred to as an “effective” composition. Furthermore, the possibility of all-optical switching, where the magnetization orientation of Tb-Fe can be reversed solely by circularly polarized laser pulses, was analyzed for a broad range of compositions and film thicknesses and correlated to the underlying magnetic properties.
TL;DR: In this paper, the authors investigated the necessary condition for the observation of all-optical helicity-dependent switching (AO-HDS) of magnetization in thin films, and they showed that both ferro-and ferrimagnets with high saturation magnetization show HDS if their magnetic thickness is strongly reduced below a material-dependent threshold thickness.
Abstract: To understand the necessary condition for the observation of all-optical helicity-dependent switching (AO-HDS) of magnetization in thin films, we investigated ferromagnetic Co/Pt and Co/Ni multilayers as well as ferrimagnetic TbCo alloys as a function of magnetic layer compositions and thicknesses. We show that both ferro-and ferrimagnets with high saturation magnetization show AO-HDS if their magnetic thickness is strongly reduced below a material-dependent threshold thickness. By taking into account the demagnetizing energy and the domain wall energy, we are able to define a criterion to predict whether AO-HDS or thermal demagnetization (TD) will be observed. This criterion for the observation of AO-HDS is that the equilibrium size of magnetic domains forming during the cooling process should be larger than the laser spot size. From these results we anticipate that more magnetic materials are expected to show AO-HDS. However, the effect of the optical pulses' helicity is hidden by the formation of small magnetic domains during the cooling process.
TL;DR: In this article, a quantitative analysis of the degradation of the magnetic properties of nonoriented electrical steel sheets caused by laser, guillotine, and spark erosion cutting as well as the healing effect of stress relief annealing is provided.
Abstract: This paper provides a quantitative analysis of the degradation of the magnetic properties of nonoriented electrical steel sheets caused by laser, guillotine, and spark erosion cutting as well as the healing effect of stress relief annealing. For this purpose, the macroscopic material characteristics, such as commutation curves, dynamic hysteresis loops, and magnetic power losses, are gained by single-sheet tester measurements. The experiments are conducted on specimens composed of strips of variable width to adjust different degrees of total degradation. The origin of the observed changes of the material is elucidated by micromagnetic measurements based on the magneto-optical Kerr effect that visualizes the domain patterns and wall movements near the cutting edges. A local magnetic contrast is defined, which serves as a quantitative measure for the local degree of deterioration. The use of homogenous parameters within a numerical loss model based on the principle of loss separation is theoretically justified and experimentally proved to provide correct values of the total magnetic power loss for arbitrary magnetizations in degraded steel sheets.
TL;DR: In this article, the authors present an experimental study of the DMI strength induced in nanometer-thick CoFeB ferromagnetic thin films in contact with different nonmagnetic metal underlayers.
Abstract: The Dzyaloshinskii-Moriya Interaction (DMI) has recently attracted considerable interest owing to its fundamental role in the stabilization of chiral spin textures in ultrathin ferromagnets, which are interesting candidates for novel spintronic technologies. Here, the authors present an experimental study of the DMI strength that is induced in nanometer-thick CoFeB ferromagnetic thin films in contact with different nonmagnetic metal underlayers. They use a novel technique for noninvasive high-sensitivity sensing of magnetic field: a scanning nanomagnetometer based on the magnetic response of a single nitrogen-vacancy defect in diamond. The magnetic domain walls are mapped, the spin structure and type of domain wall determined, and the DMI strength extracted. Importantly, the authors find local variation of the DMI constant, which clearly suggests that local field mapping techniques are extremely important to study this physics.
TL;DR: An improved conformal mapping (ICM) method for magnetic field analysis in one typical surface-mounted permanent-magnet (SMPM) motor considering the static, dynamic, and mixed rotor eccentricities is presented in this paper.
Abstract: This paper presents an improved conformal mapping (ICM) method for magnetic field analysis in one typical surface-mounted permanent-magnet (SMPM) motor considering the static, dynamic, and mixed rotor eccentricities. The ICM method accurately accounts for the slotting effect, the winding distribution, the armature reaction, the magnetic saturation effect, and the working point variation of PMs throughout their volume. The ICM method is also very rigorous to separate the onload air gap field components. First, the slotless model of an eccentric SMPM motor is mapped to one concentric model using a new form of bilinear conformal mapping, and the field solution is then obtained through applying Hague's solution in the main canonical domain. Second, the slotted air gap magnetic field is obtained through the modulation of air gap magnetic field in the slotless physical domain using the complex relative air gap permeance. The ICM method is also used to investigate the influence of rotor eccentricity on the flux linkage of the stator coils. This developed model is validated through comparing with the corresponding results obtained through finite element method and the frozen permeability method. This method can also be used as a tool for design and optimization of electrical machines.
TL;DR: In this article, the structural inversion asymmetry (SIA) gives rise to a chiral damping mechanism, which is evidenced by measuring the field-driven domain-wall (DW) motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers.
Abstract: Structural symmetry breaking in magnetic materials is responsible for the existence of multiferroics, current-induced spin-orbit torques and some topological magnetic structures In this Letter we report that the structural inversion asymmetry (SIA) gives rise to a chiral damping mechanism, which is evidenced by measuring the field-driven domain-wall (DW) motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers The DW dynamics associated with the chiral damping and those with Dzyaloshinskii-Moriya interaction (DMI) exhibit identical spatial symmetry However, both scenarios are differentiated by their time reversal properties: whereas DMI is a conservative effect that can be modelled by an effective field, the chiral damping is purely dissipative and has no influence on the equilibrium magnetic texture When the DW motion is modulated by an in-plane magnetic field, it reveals the structure of the internal fields experienced by the DWs, allowing one to distinguish the physical mechanism The chiral damping enriches the spectrum of physical phenomena engendered by the SIA, and is essential for conceiving DW and skyrmion devices owing to its coexistence with DMI (ref )
TL;DR: A tunable source of short-wavelength spin waves based on highly localized and strongly pinned magnetic domain walls in ferroelectric-ferromagnetic bilayers is proposed, enabling efficient spin wave emission at frequencies up to 100 GHz and wavelengths down to 20 nm.
Abstract: Miniaturization of magnonic devices for wave-like computing requires emission of short-wavelength spin waves, a key feature that cannot be achieved with microwave antennas. In this paper, we propose a tunable source of short-wavelength spin waves based on highly localized and strongly pinned magnetic domain walls in ferroelectric-ferromagnetic bilayers. When driven into oscillation by a microwave spin-polarized current, the magnetic domain walls emit spin waves with the same frequency as the excitation current. The amplitude of the emitted spin waves and the range of attainable excitation frequencies depend on the availability of domain wall resonance modes. In this respect, pinned domain walls in magnetic nanowires are particularly attractive. In this geometry, spin wave confinement perpendicular to the nanowire axis produces a multitude of domain wall resonances enabling efficient spin wave emission at frequencies up to 100 GHz and wavelengths down to 20 nm. At high frequency, the emission of spin waves in magnetic nanowires becomes monochromatic. Moreover, pinning of magnetic domain wall oscillators onto the same ferroelectric domain boundary in parallel nanowires guarantees good coherency between spin wave sources, which opens perspectives towards the realization of Mach-Zehnder type logic devices and sensors.
TL;DR: In this article, it was shown that magnetic mirror symmetry planes present in the stripe phase, instead of chiral exchange, determine the internal skyrmion structure and the net achirality.
Abstract: We show that properly engineered amorphous Fe-Gd alloy thin films with perpendicular magnetic anisotropy exhibit bound pairs of like-polarity, opposite helicity skyrmions at room temperature. Magnetic mirror symmetry planes present in the stripe phase, instead of chiral exchange, determine the internal skyrmion structure and the net achirality of the skyrmion phase. Our study shows that stripe domain engineering in amorphous alloy thin films may enable the creation of skyrmion phases with technologically desirable properties.
TL;DR: In this article, the spin-orbit interaction, introduced via a Kitaev term in the exchange Hamiltonian, condenses these vortices into a triangular vortex crystal at zero temperature.
Abstract: The triangular-lattice Heisenberg antiferromagnet (HAF) is known to carry topological ${\mathbb{Z}}_{2}$ vortex excitations which form a gas at finite temperatures. Here we show that the spin-orbit interaction, introduced via a Kitaev term in the exchange Hamiltonian, condenses these vortices into a triangular ${\mathbb{Z}}_{2}$ vortex crystal at zero temperature. The cores of the ${\mathbb{Z}}_{2}$ vortices show abrupt, soliton-like magnetization modulations and arise by a special intertwining of three honeycomb superstructures of ferromagnetic domains, one for each of the three sublattices of the ${120}^{\ensuremath{\circ}}$ state of the pure HAF. This is an example of a nucleation transition, analogous to the spontaneous formation of magnetic domains, Abrikosov vortices in type-II superconductors, blue phases in cholesteric liquid crystals, and skyrmions in chiral helimagnets. As the mechanism relies on the interplay of geometric frustration and spin-orbital anisotropies, such vortex mesophases can materialize as a ground state property in spin-orbit coupled correlated systems with nearly hexagonal topology, as in triangular or strongly frustrated honeycomb iridates.
TL;DR: In this article, the effects of Co addition on magnetic properties and thermal parameters of high saturation magnetic flux density (Bs) Fe83-xCoxSi2B11P3C1 (x = 0, 5, 10, 15 and 20) amorphous alloys are investigated.
TL;DR: In this paper, a spin-wave fiber using a magnetic domain structure with two domain walls was designed and demonstrated that such a spinwave fiber can transmit spin waves over long distances by total internal reflections, in analogy to an optical fiber.
Abstract: Spin waves are collective excitations propagating in the magnetic medium with ordered magnetizations. Magnonics, utilizing the spin wave (magnon) as an information carrier, is a promising candidate for low-dissipation computation and communication technologies. We discover that, due to the Dzyaloshinskii-Moriya interaction, the scattering behavior of the spin wave at a magnetic domain wall follows a generalized Snell's law, where two magnetic domains work as two different mediums. Similar to optical total reflection that occurs at water-air interfaces, spin waves may experience total reflection at the magnetic domain walls when their incident angle is larger than a critical value. We design a spin-wave fiber using a magnetic domain structure with two domain walls, and demonstrate that such a spin-wave fiber can transmit spin waves over long distances by total internal reflections, in analogy to an optical fiber.
TL;DR: In this article, high-resolution magnetic x-ray spectromicroscopy at xray photon energies near the cobalt L3 resonance was applied to probe an amorphous 50 nm thin SmCo5 film prepared by off-axis pulsed laser deposition onto an xray transparent Si3N4 membrane.
Abstract: High spatial resolution magnetic x-ray spectromicroscopy at x-ray photon energies near the cobalt L3 resonance was applied to probe an amorphous 50 nm thin SmCo5 film prepared by off-axis pulsed laser deposition onto an x-ray transparent 200 nm thin Si3N4 membrane. Alternating gradient magnetometry shows a strong in-plane anisotropy and an only weak perpendicular magnetic anisotropy, which is confirmed by magnetic transmission soft x-ray microscopy images showing over a field of view of 10 μm a primarily stripe-like domain pattern but with local labyrinth-like domains. Soft x-ray ptychography in amplitude and phase contrast was used to identify and characterize local magnetic and structural features over a field of view of 1 μm with a spatial resolution of about 10 nm. There, the magnetic labyrinth domain patterns are accompanied by nanoscale structural inclusions that are primarily located in close proximity to the magnetic domain walls. Our analysis suggests that these inclusions are nanocrystalline Sm2...
TL;DR: In this article, an improved conformal mapping (ICM) method was proposed for the separation of the on-load air-gap magnetic field components in surface-mounted permanent magnet (SPM) motors under loading conditions.
Abstract: This paper introduces an improved conformal mapping (ICM) method for the separation of the on-load air-gap magnetic field components in surface-mounted permanent-magnet (SPM) motors under loading conditions. The ICM method can model the magnetic induction inside a permanent magnet (PM) due to the armature reaction and the relative recoil permeability. The ICM method can also consider the simultaneous influences of the armature reaction, the slotting effect, the magnetic saturation, and the relative recoil permeability in the determination of operating points of the PM in its different parts. Therefore, this proposed method can be useful for an on-load performance analysis of SPM motors. Three conformal mappings are used to reach the main canonical domain: two logarithmic complex functions and the Schwarz–Christoffel (SC) mapping. The field solution in the slotless domain is then mapped back into the slotted domain using the complex air-gap permeance. The field solution in the slotted domain is used to calculate the on-load air-gap field components due to the PMs and the armature reaction. These on-load field components allow the calculation of the on-load PM flux linkage, the on-load PM back-EMF, and the on-load torque components. The influences of electric loading on the on-load torque components and the on-load PM back-EMF are studied using the ICM method. The on-load cogging torque periodicity is confirmed to change due to the magnetic saturation, and the harmonic content of torque components and the PM back-EMF is also altered due to the electric loading. The accuracy of this developed model is verified by comparing the results obtained through the ICM method with the respective results obtained through the finite-element analysis and the frozen permeability method.
TL;DR: The broad inhomogeneous FMR line-width, observation of the Verwey transition, tuning of the magnetic domain structure as well as the magnetic properties suggest that the NiCoFe2O4 ferrite NPs may be promising for future generation spintronics, magneto-electronics, and ultra-high-density recording media as well for radar absorbing applications.
Abstract: Magnetic anomalies corresponding to the Verwey transition and reorientation of anisotropic vacancies are observed at 151 K and 306 K, respectively, in NiCoFe2O4 nanoparticles (NPs) synthesized by a modified-solvothermal method followed by annealing. Cationic disorder and spherical shape induced non-stoichiometry suppress the Verwey transition in the as-synthesized NPs. On the other hand, reorientation of anisotropic vacancies is quite robust. XRD and electron microscopy investigations confirm a single phase spinel structure and the surface morphology of the as-synthesized NPs changes from spherical to octahedral upon annealing. Rietveld analysis reveals that the Ni(2+) ions migrate from tetrahedral (A) to octahedral (B) sites upon annealing. The Mossbauer results show canted spins in both the NPs and the strength of superexchange is stronger in Co-O-Fe than Ni-O-Fe. Magnetic force images show that the as-synthesised NPs are single-domain whereas the annealed NPs are multi-domain octahedral particles. The FMR study reveals that both the NPs have a broad FMR line-width; and resonance properties are consistent with the random anisotropy model. The broad inhomogeneous FMR line-width, observation of the Verwey transition, tuning of the magnetic domain structure as well as the magnetic properties suggest that the NiCoFe2O4 ferrite NPs may be promising for future generation spintronics, magneto-electronics, and ultra-high-density recording media as well as for radar absorbing applications.
TL;DR: The detailed description of the remanent state in diameter-modulated cylindrical FeCoCu nanowires allows a clear explanation of the origin of bright and dark contrast observed in magnetic force microscopy images, which have the same feature of magnetic domain walls.
Abstract: The comprehension of the magnetic configuration in FeCoCu nanowires with a diameter-modulated cylindrical geometry will allow controlling the domain wall motion in this low-dimensional system under the application of magnetic fields and/or the injection of current pulses. Here we perform a quantitative magnetic characterization of isolated diameter-modulated FeCoCu nanowires by combining nanoscale magnetic characterization techniques such as electron holography, magnetic force microscopy, and micromagnetic simulations. Local reconstructions of the magnetic distribution show the diameter-modulated geometry of the wires induces the formation of vortex-like structures and magnetic charges in the regions where the diameter is varied. Vortex-like structures modify the axial alignment of the magnetization in large-diameter segments. Moreover, the magnetic charges control the demagnetizing field distribution, promoting a flux-closure stray field configuration around large-diameter segments and keeping the demagn...