Showing papers on "Single domain published in 2016"
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 structural and magnetic properties of chemically synthesized magnetite nanoparticles have been studied using X-ray diffraction, transmission electron microscopy and Vibrating Sample Magnetometer.
124 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: 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.
93 citations
TL;DR: Experimental manipulation of the magnetic states of elliptical cobalt magnetostrictive nanomagnets delineated on bulk 128° Y-cut lithium niobate with acoustic waves launched from interdigitated electrodes could lead to the development of extremely energy efficient magnetization switching methodologies for low-power computing applications.
Abstract: We report experimental manipulation of the magnetic states of elliptical cobalt magnetostrictive nanomagnets (with nominal dimensions of ∼340 nm × 270 nm × 12 nm) delineated on bulk 128° Y-cut lithium niobate with acoustic waves (AWs) launched from interdigitated electrodes. Isolated nanomagnets (no dipole interaction with any other nanomagnet) that are initially magnetized with a magnetic field to a single-domain state with the magnetization aligned along the major axis of the ellipse are driven into a vortex state by acoustic waves that modulate the stress anisotropy of these nanomagnets. The nanomagnets remain in the vortex state until they are reset by a strong magnetic field to the initial single-domain state, making the vortex state nonvolatile. This phenomenon is modeled and explained using a micromagnetic framework and could lead to the development of extremely energy efficient magnetization switching methodologies for low-power computing applications.
76 citations
TL;DR: In this paper, the effect of annealing temperature on the structure, morphology and magnetic properties of tin spinel ferrites doped manganese (Sn 1− x Mn x Fe 2 O 4 with x = 0.25, 0.75, and 1) nanoparticles prepared by co-precipitation method was investigated.
73 citations
TL;DR: Samarium doped M-type strontium hexaferrites with chemical formula Sr1−xSmxFe12O19 (0≤x≤0.15) (SrM) were synthesized using the proteic sol-gel process.
68 citations
TL;DR: It is shown that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains.
Abstract: Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength.
68 citations
TL;DR: In this article, the authors used transmission electron microscope (TEM) and magnetic methods to demonstrate the widespread preservation of silicate-hosted magnetic inclusions in marine sedimentary settings.
Abstract: Magnetic mineral inclusions occur commonly within other larger mineral phases in igneous rocks and have been demonstrated to preserve important paleomagnetic signals. While the usefulness of magnetic inclusions in igneous rocks have been explored extensively, their presence in sediments has only been speculated upon. The contribution of magnetic inclusions to the magnetization of sediments, therefore, has been elusive. In this study, we use transmission electron microscope (TEM) and magnetic methods to demonstrate the widespread preservation of silicate-hosted magnetic inclusions in marine sedimentary settings. TEM analysis reveals detailed information about the microstructure, chemical composition, grain size, and spatial arrangement of nanoscale magnetic mineral inclusions within larger silicate particles. Our results confirm the expectation that silicate minerals can protect magnetic mineral inclusions from sulfate-reducing diagenesis, and increase significantly the preservation potential of iron oxides in inclusions. Magnetic inclusions should, therefore, be considered as a potentially important source of fine-grained magnetic mineral assemblages, and represent a missing link in a wide range of sedimentary paleomagnetic and environmental magnetic studies. In addition, we present depositional remanent magnetization (DRM) modeling results to assess the paleomagnetic recording capability of magnetic inclusions. Our simulation demonstrates that deposition of larger silicate particles with magnetic inclusions will be controlled by gravitational and hydrodynamic forces rather than by geomagnetic torques. Thus, even though these large silicates may contain ideal single domain particles, they can not contribute meaningfully to paleomagnetic recording. However, smaller silicate grains (e.g., silt- and clay-sized) silicates with unidirectionally magnetized magnetic inclusions can potentially record a reliable DRM.
64 citations
TL;DR: In this article, a fuzzy c-means clustering technique was used to recover a 3D distribution of magnetization by using a small number of possible orientations and thereby achieves stability in recovered magnetization directions.
Abstract: The presence of remanent magnetization has hindered the application of generalized 3D magnetic inversion in exploration geophysics because of the unknown and variable magnetization directions. Although many authors have developed different approaches to deal with this difficulty, it remains a challenge. We have developed a new approach for inverting the total-field magnetic anomaly to recover a 3D distribution of magnetization by using a fuzzy c-means clustering technique. The inversion approximates the variation of magnetization directions with a small number of possible orientations and thereby achieves stability in recovered magnetization directions and improves the spatial imaging of magnetization magnitude. We have also found that the inverted magnetization directions can yield more information than does a standard magnetic susceptibility inversion and provide a new opportunity for magnetic interpretation. The magnitude of magnetization helps to define the configuration and structure of causa...
54 citations
TL;DR: In this paper, the pinning effect of the periodic diameter modulations on the domain wall propagation in FeCoCu individual nanowires is determined by Magnetic Force Microscopy, MFM.
Abstract: The three dimensional nature of cylindrical magnetic nanowires has opened a new way to control the domain configuration as well as the magnetization reversal process. The pinning effect of the periodic diameter modulations on the domain wall propagation in FeCoCu individual nanowires is determined by Magnetic Force Microscopy, MFM. A main bistable magnetic configuration is firstly concluded from MFM images characterized by the spin reversal between two nearly single domain states with opposite axial magnetization. Complementary micromagnetic simulations confirm a vortex mediated magnetization reversal process. A non-standard variable field MFM imaging procedure allows us to observe metastable magnetic states where the propagating domain wall is pinned at certain positions with enlarged diameter. Moreover, it is demonstrated that it is possible to control the position of the pinned domain walls by an external magnetic field.
TL;DR: It is demonstrated that Fe3O4 grains containing vortex structures are indeed reliable recorders of paleodirectional and paleointensity information, and the presence of PSD magnetic signals does not preclude the successful recovery of paleomagnetic signals.
Abstract: The study of the paleomagnetic signal recorded by rocks allows scientists to understand Earth’s past magnetic field and the formation of the geodynamo. The magnetic recording fidelity of this signal is dependent on the magnetic domain state it adopts. The most prevalent example found in nature is the pseudo–single-domain (PSD) structure, yet its recording fidelity is poorly understood. Here, the thermoremanent behavior of PSD magnetite (Fe3O4) particles, which dominate the magnetic signatures of many rock lithologies, is investigated using electron holography. This study provides spatially resolved magnetic information from individual Fe3O4 grains as a function of temperature, which has been previously inaccessible. A small exemplar Fe3O4 grain (~150 nm) exhibits dynamic movement of its magnetic vortex structure above 400°C, recovering its original state upon cooling, whereas a larger exemplar Fe3O4 grain (~250 nm) is shown to retain its vortex state on heating to 550°C, close to the Curie temperature of 580°C. Hence, we demonstrate that Fe3O4 grains containing vortex structures are indeed reliable recorders of paleodirectional and paleointensity information, and the presence of PSD magnetic signals does not preclude the successful recovery of paleomagnetic signals.
TL;DR: In this article, the magnetic architecture of a single dusty olivine grain from the Semarkona LL3.0 ordinary chondrite meteorite can be fully characterized in three dimensions, using a combination of focused ion beam nanotomography (FIB-nT), electron tomography, and finite-element micromagnetic modeling.
Abstract: Dusty olivine (olivine containing multiple sub-micrometer inclusions of metallic iron) in chondritic meteorites is considered an ideal carrier of paleomagnetic remanence, capable of maintaining a faithful record of pre-accretionary magnetization acquired during chondrule formation. Here we show how the magnetic architecture of a single dusty olivine grain from the Semarkona LL3.0 ordinary chondrite meteorite can be fully characterized in three dimensions, using a combination of focused ion beam nanotomography (FIB-nT), electron tomography, and finite-element micromagnetic modeling. We present a three-dimensional (3D) volume reconstruction of a dusty olivine grain, obtained by selective milling through a region of interest in a series of sequential 20 nm slices, which are then imaged using scanning electron microscopy. The data provide a quantitative description of the iron particle ensemble, including the distribution of particle sizes, shapes, interparticle spacings and orientations. Iron particles are predominantly oblate ellipsoids with average radii 242 ± 94 × 199 ± 80 × 123 ± 58 nm. Using analytical TEM we observe that the particles nucleate on sub-grain boundaries and are loosely arranged in a series of sheets parallel to (001) of the olivine host. This is in agreement with the orientation data collected using the FIB-nT and highlights how the underlying texture of the dusty olivine is crystallographically constrained by the olivine host. The shortest dimension of the particles is oriented normal to the sheets and their longest dimension is preferentially aligned within the sheets. Individual particle geometries are converted to a finite-element mesh and used to perform micromagnetic simulations. The majority of particles adopt a single vortex state, with “bulk” spins that rotate around a central vortex core. We observed no particles that are in a true single domain state. The results of the micromagnetic simulations challenge some preconceived ideas about the remanence-carrying properties of vortex states. There is often not a simple predictive relationship between the major, intermediate, and minor axes of the particles and the remanence vector imparted in different fields. Although the orientation of the vortex core is determined largely by the ellipsoidal geometry (i.e., parallel to the major axis for prolate ellipsoids and parallel to the minor axis for oblate ellipsoids), the core and remanence vectors can sometimes lie at very large (tens of degrees) angles to the principal axes. The subtle details of the morphology can control the overall remanence state, leading in some cases to a dominant contribution from the bulk spins to the net remanence, with profound implications for predicting the anisotropy of the sample. The particles have very high switching fields (several hundred millitesla), demonstrating their high stability and suitability for paleointensity studies.
TL;DR: In this article, the influence of Mn contents on structural parameters, morphological characteristics and magnetic properties of ZnFe 2 O 4 ferrite samples was explored, and the impact of average grain dimensions on magnetic properties inferred from multi domain and single domain particle's effect was also analyzed.
21 Oct 2016
TL;DR: In this article, a systematic magnetic force microscopy (MFM) study of domain behavior in thin films of the magnetic topological insulator Sb1.89V0.11Te3 reveals that after zero-field cooling, an equal population of up and down domains occurs.
Abstract: A systematic magnetic force microscopy (MFM) study of domain behavior in thin films of the magnetic topological insulator Sb1.89V0.11Te3 reveals that in the virgin domain state, after zero-field cooling, an equal population of up and down domains occurs. Interestingly, the cooling field dependence of MFM images demonstrates that a small cooling magnetic field (approximately 5–10 Oe) is sufficient to significantly polarize the film despite the coercive field (HC) for these films being on the order of a tesla at low temperature. By visualizing the magnetization reversal process around HC of V-doped Sb2Te3, we observed a typical domain behavior of a ferromagnet, i.e., domain nucleation and domain wall propagation. Our results provide direct evidence of ferromagnetic behavior of the magnetic topological insulator, a necessary condition for a robust quantum anomalous Hall effect. Direction visualization of magnetic domains in a doped topological insulator suggests ferromagnetic behaviour, satisfying one of the necessary conditions for a quantum anomalous Hall effect. Cryogenic magnetic force microscopy measurements of V-doped Sb2Te3 thin films reveals equal proportions of up and down domains- a zero magnetic state—after zero-field cooling. The subsequent application of a small external magnetic field significantly polarizes the magnetization of the film, with an increasing field enhancing the effect. In addition, visualization of domain reversal around the coercive field point reveals domain nucleation and domain wall propagation, hallmarks of typical ferromagnets. Ferromagentism induced by chemical doping of topological insulator is one approach towards achieving the quantum anomalous Hall effect, while the stability of the single domain state in V-doped Sb2Te3 is crucial for observing such effect in zero magnetic field.
TL;DR: In this article, the robust nucleation of magnetic domain walls in cylindrical permalloy nanowires is described, and specific features of the magnetic force microscopy contrast of such wires are discussed, to avoid the misinterpretation of the magnetization states.
Abstract: We report several procedures for the robust nucleation of magnetic domain walls in cylindrical permalloy nanowires. Specific features of the magnetic force microscopy (MFM) contrast of such wires are discussed, to avoid the misinterpretation of the magnetization states. The domain walls moved under quasistatic magnetic fields in the range 0.1–10 mT, as evidenced by MFM at remanence at different stages of their motion.
TL;DR: In this article, the magnetic domain structures of MgO/CoFeB with a perpendicular magnetic easy axis under an electric field were observed and the domain structure showed a maze pattern with electric-field dependent isotropic period.
Abstract: We observe magnetic domain structures of MgO/CoFeB with a perpendicular magnetic easy axis under an electric field. The domain structure shows a maze pattern with electric-field dependent isotropic period. The analysis of the period indicates a major role of the electric-field modulation of interfacial magnetic anisotropy for the observation and possible contribution from electric-field modulation of the exchange stiffness constant.
TL;DR: Measurements show that the Π-shaped stripline can deterministically write a magnetic data bit in 15 ns even with a relatively low current density, and it is demonstrated experimentally that the injection geometry can perform bit writing using only about 30% of the electrical energy as compared to a conventional injection line.
Abstract: Electrical injection of magnetic domain walls in perpendicular magnetic anisotropy nanowire is crucial for data bit writing in domain wall-based magnetic memory and logic devices. Conventionally, the current pulse required to nucleate a domain wall is approximately ~1012 A/m2. Here, we demonstrate an energy efficient structure to inject domain walls. Under an applied electric potential, our proposed Π-shaped stripline generates a highly concentrated current distribution. This creates a highly localized magnetic field that quickly initiates the nucleation of a magnetic domain. The formation and motion of the resulting domain walls can then be electrically detected by means of Ta Hall bars across the nanowire. Our measurements show that the Π-shaped stripline can deterministically write a magnetic data bit in 15 ns even with a relatively low current density of 5.34 × 1011 A/m2. Micromagnetic simulations reveal the evolution of the domain nucleation – first, by the formation of a pair of magnetic bubbles, then followed by their rapid expansion into a single domain. Finally, we also demonstrate experimentally that our injection geometry can perform bit writing using only about 30% of the electrical energy as compared to a conventional injection line.
TL;DR: In this article, the authors show that the magnetic layer single domain ground state consists of magnetizations that can be significantly canted with respect to the layer planes and the canting can be tuned by varying the Ru thickness and the layer magnetic characteristics, a capability of interest for applications in spin-transfer torque devices.
Abstract: Interlayer exchange coupling between layers with perpendicular and easy-plane magnetic anisotropies separated by a non-magnetic spacer is studied using ferromagnetic resonance. The samples consist of a Co/Ni multilayer with perpendicular magnetic anisotropy and a CoFeB layer with easy-plane anisotropy separated by a variable thickness Ru layer. At a fixed frequency, we show that there is an avoided crossing of layer ferromagnetic resonance modes providing direct evidence for interlayer coupling. The mode dispersions for different Ru thicknesses are fit to a Heisenberg-type model to determine the interlayer exchange coupling strength and layer properties. The resulting interlayer exchange coupling varies continuously from antiferromagnetic to ferromagnetic as a function of the Ru interlayer thickness. These results show that the magnetic layer single domain ground state consists of magnetizations that can be significantly canted with respect to the layer planes and the canting can be tuned by varying the Ru thickness and the layer magnetic characteristics, a capability of interest for applications in spin-transfer torque devices.
TL;DR: In this paper, the low temperature behavior of densely packed interacting spherical single domain nanoparticles (MNP) is investigated by Monte Carlo simulations in the framework of an effective one spin model, where particles are distributed through a hard sphere like distribution with periodic boundary conditions and interact through the dipole dipole interaction (DDI) with an anisotropy energy including both cubic and uniaxial symmetry components.
TL;DR: In this paper, the dominant magnetization mechanism was investigated by resolving the complex permeability spectra into two components including domain wall movement and spin rotation magnetization, and the results showed that the dominant contribution to magnetisation mechanism changes from spin-rotation magnetization to domain-wall movement due to the increase of amount of domain wall, which is observed by Lorentz microscopy to measure the critical diameter of magnetic domain in NiZn ferrite.
01 Apr 2016
TL;DR: In this article, the effect of milling time on the magnetic properties of single-domain strontium hexaferrite particles with hexagonal morphology has been investigated and it was shown that the magnetization process was significantly influenced with different milling times.
Abstract: Single domain strontium ferrite particles (SrFe12O19) with hexagonal morphology were synthesized by conventional ceramic process. Effects of Fe/Sr mole ratio and milling time on structure, morphology and magnetic properties of the strontium ferrite particles have been systematically studied. Single phase SrFe12O19 was successfully synthesized in a large composition range of Fe/Sr ratio (Fe/Sr = 9–11). The particle size refinement effect and the morphology change were observed with the increase of Fe/Sr ratio. It was also found that the change of Fe/Sr ratio had little effect on the magnetization curve. However, the magnetization process was significantly influenced with different milling time. The optimal magnetic properties obtained at Fe/Sr = 11 with 6 h milling are 68.2 emu g−1 and 5540 Oe for saturation magnetization (M S) and intrinsic coercivity (H C), respectively. The high performance single domain strontium hexaferrite particles obtained in this paper would greatly facilitate the application in the permanent magnet industry.
TL;DR: In this paper, the influence of magnetic history on the topology of perpendicular magnetic domains in a thin ferromagnetic film made of [Co(8 A)/Pt(7 A)] 50 multilayers was studied.
TL;DR: In this article, the dominant existence of single domain particles with Co substitution over superparamagnetic particles in non-substituted nickel zinc ferrites with the general formula CoxNi0.6−xZn0.4Fe2O4 was investigated.
Abstract: Nanocrystalline Co substituted Ni–Zn ferrites with the general formula CoxNi0.6−xZn0.4Fe2O4 (x = 0.0 to 0.6) were prepared by a precursor combustion method. Average crystallite size, as estimated by using a Scherrer method and the particle size obtained from transmission electron microscopy (TEM) techniques, was found to be in the range of 10–30 nm. EDX and XRD analysis confirms the presence of Co, Ni, Zn, Fe and oxygen and the desired phases in the prepared nanoparticles. Selective area electron diffraction (SAED) analysis confirms the crystalline nature of the prepared nanoparticles. It is observed that Co substitution has a pronounced effect on the magnetic properties such as MR, MS and HC and also on the Curie temperature (TC), which is found to decrease from 420 °C for non-substituted Ni–Zn ferrites to 325 °C for the highest substitution of x = 0.6. These effects are assigned to the higher magnetocrystalline anisotropy of Co than Ni and to the size dependent existence of single domain–superparamagnetic particles distribution. Comparatively, the dominant existence of single domain particles with Co substitution over superparamagnetic particles in non-substituted nickel zinc ferrites is extensively investigated in this article.
TL;DR: In this paper, the magnetic properties of toroidal nanomagnets have been studied by means of micromagnetic simulations, and the magnetization ground state for different values of the aspect ratio between the toroidal and polar radii of the nanotorus has been obtained.
Abstract: In this work, and by means of micromagnetic simulations, we study the magnetic properties of toroidal nanomagnets. The magnetization ground state for different values of the aspect ratio between the toroidal and polar radii of the nanotorus has been obtained. Besides, we have shown that the vortex and the in-plane single domain states can appear as ground states for different ranges of the aspect ratio, while a single domain state with an out-of-plane magnetization is not observed. The hysteresis curves are also obtained, evidencing the existence of two reversal modes depending on the geometry: a vortex mode and a coherent rotation. A comparison between toroidal and cylindrical nanoparticles has been performed evidencing that nanotori can accommodate a vortex as the ground state for smaller volume than cylindrical nanorings.
TL;DR: In this paper, the authors show that by controlling the unidirectional anisotropy of a continuous ferromagnetic film through exchange bias, domain walls whose spin arrangement is generally not favored by dipolar and exchange interactions can be created.
TL;DR: In this article, the effect of an inhomogeneous magnetoelectric coupling on the magnon-induced dynamics of a ferromagnet was considered, and it was shown that the applied electric field can also be used to tune the domain wall speed and direction of motion in a linear fashion.
Abstract: We consider theoretically the effect of an inhomogeneous magnetoelectric coupling on the magnon-induced dynamics of a ferromagnet. The magnon-mediated magnetoelectric torque affects both the homogeneous magnetization and magnon-driven domain wall motion. In the domains, we predict a reorientation of the magnetization, controllable by the applied electric field, which is almost an order of magnitude larger than that observed in other physical systems via the same mechanism. The applied electric field can also be used to tune the domain wall speed and direction of motion in a linear fashion, producing domain wall velocities several times the zero field velocity. These results show that multiferroic systems offer a promising arena to achieve low-dissipation magnetization rotation and domain wall motion by exciting spin-waves.
TL;DR: In this paper, the modification of magnetic domain in perpendicularly magnetized Co/Pt multilayer by using ultrashort laser pulse was demonstrated, where 50% reduction in anisotropy energy is observed with increasing the total energy of the system and a sharp increase in demagnetization energy also takes place simultaneously.