Showing papers on "Magnetic domain published in 2023"

Synergistic Dielectric–Magnetic Enhancement via Phase‐Evolution Engineering and Dynamic Magnetic Resonance

Abstract: Dielectric polarization and magnetic resonance associated with intrinsic constituent and extrinsic structure are two kinds of fundamental attenuation mechanisms for microwave absorbers, but remain extremely challenging in revealing the composition‐morphology‐performance correlation. Herein, hierarchical MXene/metal‐organic framework derivatives with coherent boundaries and magnetic units below critical grain size are constructed to realize synergistic dielectric–magnetic enhancement by phase‐evolution engineering and dynamic magnetic resonance. Specifically, phase‐evolution induced inseparable interfaces, diverse incompatible phases, and defects/vacancies contribute to dielectric polarization, while closely distributed magnetic units simultaneously realize nanoscale multi‐domain coupling and long‐range magnetic interaction. As results, the hierarchical derivatives promise an exceptional reflection loss of −59.5 dB and an effective absorption bandwidth of 6.1 GHz. Both experimental results and theoretical calculations indicate that phase‐evolution engineering and dynamic magnetic resonance maximize the absorption capability and demonstrate a versatile methodology for manipulating microwave attenuation. More importantly, the proposed multi‐domain coupling and long‐range magnetic interaction theories innovatively offer dynamic magnetic resonance mechanism for magnetic loss within critical grain size.

Hard ferrite magnetic insulators revealing giant coercivity and sub-terahertz natural ferromagnetic resonance at 5-300 K.

Abstract: The temperature behavior of the magnetic properties is crucial for the application of magnetic materials. Recently, giant room temperature coercivities (20-36 kOe) and sub-terahertz natural ferromagnetic resonance (NFMR) frequencies (160-250 GHz) were observed for single-domain M-type hexaferrites with high aluminum substitution. Herein, the temperature dependences of the magnetic properties and natural ferromagnetic resonance are studied at 5-300 K for single-domain Sr1-x/12Cax/12Fe12-xAlxO19 (x = 1.5-5.5) particles. It is shown that the samples maintain their magnetic hardness over the whole temperature range. The coercivity and NFMR frequencies have a maximum shifting to the low-temperature region with a rise in aluminum concentration. The highest coercivity of 42 kOe and the maximum NFMR frequency of 297 GHz are observed for x = 5.5 at 180 K.

Thickness-dependent magnetic properties in Pt/[Co/Ni] n multilayers with perpendicular magnetic anisotropy

Abstract: We systematically investigated the Ni and Co thickness-dependent perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain structures, and magnetization dynamics of Pt(5 nm)/[Co(t Co)/Ni(t Ni)]5/Pt(1 nm) multilayers by combining the four standard magnetic characterization techniques. The magnetic-related hysteresis loops obtained from the field-dependent magnetization M and anomalous Hall resistivity (AHR) ρxy showed that the two serial multilayers with t Co = 0.2 nm and 0.3 nm have the optimum PMA coefficient K U as well as the highest coercivity H C at the Ni thickness t Ni = 0.6 nm. Additionally, the magnetic domain structures obtained by magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the thickness and K U of the films. Furthermore, the thickness-dependent linewidth of ferromagnetic resonance is inversely proportional to K U and H C, indicating that inhomogeneous magnetic properties dominate the linewidth. However, the intrinsic Gilbert damping constant determined by a linear fitting of the frequency-dependent linewidth does not depend on the Ni thickness and K U. Our results could help promote the PMA [Co/Ni] multilayer applications in various spintronic and spin-orbitronic devices.

Accurate calculation of global hysteresis properties of grain-oriented silicon steel based on an improved J-A model with variable parameters

Abstract: Based on the consideration of the magnetic domain motion under different magnetization levels, an improved J-A model with variable parameters is proposed to solve the problem of significant errors in the process of calculating the inner symmetric small loops. The proposed method introduces a variable scale parameter v( B) to correct the irreversible magnetization component of the J-A model. Meanwhile, based on the magnetic domain theory, a method with variable pinning parameter k( B) and a variable domain wall bending parameter c( B) is proposed. By comparing the measured data of B30P105 Grain-Oriented (GO) silicon steel, the calculation error for each magnetization level of the model is within 7%, which means that the global hysteresis properties of GO silicon steel can be well reproduced.

The origin of magnetization-caused increment in water oxidation

Abstract: Magnetization promoted activity of magnetic catalysts towards the oxygen evolution reaction (OER) has attracted great attention, but remains a puzzle where the increment comes from. Magnetization of a ferromagnetic material only changes its magnetic domain structure. It does not directly change the spin orientation of unpaired electrons in the material. The confusion is that each magnetic domain is a small magnet and theoretically the spin-polarization promoted OER already occurs on these magnetic domains, and thus the enhancement should have been achieved without magnetization. Here, we demonstrate that the enhancement comes from the disappeared domain wall upon magnetization. Magnetization leads to the evolution of the magnetic domain structure, from a multi-domain one to a single domain one, in which the domain wall disappears. The surface occupied by the domain wall is reformatted into one by a single domain, on which the OER follows the spin-facilitated pathways and thus the overall increment on the electrode occurs. This study fills the missing gap for understanding the spin-polarized OER and it further explains the type of ferromagnetic catalysts which can give increment by magnetization.

A Study of Stress – Induced Subtle Magnetic Changes in a Mild Steel using Barkhausen Emission-Aided Analysis Approaches

Abstract: In this study magnetic Barkhausen emission – based approaches were used to reveal and characterize some interesting elastic stress - induced quantitative and qualitative subtle changes in the micromagnetic activity of steels. The quantitative changes consist in a multiplication of domain walls whereas the qualitative in the formation of two major modes of domain wall motion. Concerning the first kind of changes, it was shown that the experimentally obtained low limit of elastic stress at which such micromagnetic changes may occur is in reasonable agreement with existing theoretical as well as experimental results. Concerning the second kind of changes, it was shown by means of two types of distribution approach, that these two modes of wall motion may be related to the grain boundaries as well as the grain interior micromagnetic activity. In this context, it was also shown that an increase in the supplied elastic strain leads to a broadening of both distribution modes.

Domain-wall magnetoelectric coupling in multiferroic hexagonal YbFeO3 films

Abstract: Abstract Electrical modulation of magnetic states in single-phase multiferroic materials, using domain-wall magnetoelectric (ME) coupling, can be enhanced substantially by controlling the population density of the ferroelectric (FE) domain walls during polarization switching. In this work, we investigate the domain-wall ME coupling in multiferroic h-YbFeO 3 thin films, in which the FE domain walls induce clamped antiferromagnetic (AFM) domain walls with reduced magnetization magnitude. Simulation according to the phenomenological theory indicates that the domain-wall ME effect is dramatically enhanced when the separation between the FE domain walls shrinks below the characteristic width of the clamped AFM domain walls during the ferroelectric switching. Experimentally, we show that while the magnetization magnitude remains same for both the positive and the negative saturation polarization states, there is evidence of magnetization reduction at the coercive voltages. These results suggest that the domain-wall ME effect is viable for electrical control of magnetization.

Magnetization State and Magnetic Structure of Wiegand Wire Evaluated by External Magnetic Field Measurement

Abstract: Wiegand wires exhibit unique and fast magnetization reversal features, termed as large Barkhausen jumps, in externally applied alternating magnetic fields. However, the mechanisms and magnetization states yielding these large Barkhausen jumps are yet to be sufficiently elucidated. Thus, in this study, we analyzed the magnetization state and magnetic structure of a Wiegand wire by measuring the magnetic field of the wire. Moreover, we defined a four-layer magnetic structure model of the Wiegand wire and analyzed the magnetization states and processes of these layers in an applied alternating magnetic field. Additionally, we determined the switching field of each layer and specified the magnetization states resulting in the large Barkhausen jump.

The magneto-mechanic hysteresis model for giant magnetostrictive materials based on the magnetic domain theory

Abstract: In the paper, a magneto-mechanic hysteresis model for giant magnetostrictive materials is suggested by considering the effect of the domain rotation and domain wall motion on the magnetization process under prestress and the applied magnetic field. The coercive force, which is magneto-mechanic dependent, is proposed instead of a pinning constant in the Jiles–Atherton model. The model can well predict the characteristics of a magnetization-applied field curve and magnetostrictive strain-applied field curve shown in the experiment, especially the “overturn phenomenon” under different compressive prestresses. Furthermore, the effect of the microstructure parameter, such as the ratio of the domain wall thickness to the internal stress wavelength, the amplitude of internal stress, the ratio of the domain wall thickness to the inclusion radius, and inclusion consistency, on coercive force under applied prestress can also be described by the model. The comparison between the results predicted by the model and experiment shows that the model is suited for a wide-ranging applied magnetic field.

Multi‐Domain versus Single‐Domain: A Magnetic Field is Not a Must for Promoting Spin‐Polarized Water Oxidation

Abstract: The reaction kinetics of spin-polarized oxygen evolution reaction (OER) can be enhanced by ferromagnetic (FM) catalysts under an external magnetic field. However, applying a magnetic field necessitates additional energy consumption and creates design difficulties for OER. Herein, we demonstrate that a single-domain FM catalyst without external magnetic fields exhibits a similar OER increment to its magnetized multi-domain one. The evidence is given by comparing the pH-dependent increment of OER on multi- and single-domain FM catalysts with or without a magnetic field. The intrinsic activity of a single-domain catalyst is higher than that of a multi-domain counterpart. The latter can be promoted to approach the former by the magnetization effect. Reducing the FM catalyst size into the single-domain region, the spin-polarized OER performance can be achieved without a magnetic field, illustrating an external magnetic field is not a requirement to reap the benefits of magnetic catalysts.

Magnetic bubbles with alternating chirality in domain walls

Abstract: In magnetic multilayers with perpendicular anisotropy, the competition of short-range and long-range interactions gives rise to the stability of cylindrical magnetic domains, also known as magnetic bubbles. The presence of Dzyaloshinsky-Moriya interaction induced by asymmetric interfaces between magnetic and nonmagnetic layers may lead to the formation of cylindrical bubble domains with Neel-type domain walls across the whole thickness of the multilayer. Such domain walls produce no contrast in Lorentz TEM under the normal incidence of the electron beam to the film. The latter is often used as an argument for the presence of Dzyaloshinskii-Moriya interaction in the system. Here we show that in magnetic multilayers, the absence of the Lorentz TEM contrast might also have another origin. In particular, in the absence of interfacial Dzyaloshinskii-Moriya interaction and weak interlayer exchange coupling, the magnetic bubbles might have Bloch-type domain walls of alternate chirality in adjacent layers. Such domain walls also do not produce magnetic contrast in Lorentz TEM at normal incidence of the electron beam. We show that, in the absence of interlayer exchange coupling, the magnetic bubble domains with the domain walls of fixed and alternate chirality have nearly identical energies and can coexist in the same range of magnetic fields. Using the geodesic nudged elastic band method, we prove that these states are separated by finite energy barriers. Furthermore, we demonstrate that magnetic multilayers with only dipolar coupling, besides the magnetic bubbles with nontrivial topology in all layers, can accommodate solutions with trivial topology within the internal layers.

Magnetic domain walls : Types, processes and applications

Abstract: Domain walls (DWs) in magnetic nanowires are promising candidates for a variety of applications including Boolean/unconventional logic, memories, in-memory computing as well as magnetic sensors and biomagnetic implementations. They show rich physical behaviour and are controllable using a number of methods including magnetic fields, charge and spin currents and spin-orbit torques. In this review, we detail types of domain walls in ferromagnetic nanowires and describe processes of manipulating their state. We look at the state of the art of DW applications and give our take on the their current status, technological feasibility and challenges.

Kittel’s model for ferromagnetic domains, revised and completed, including the derivation of the magnetic hysteresis

Abstract: In 1946 and 1949, Charles Kittel proposed a simple model for the size of ferromagnetic domains that is still widely used nowadays [C. Kittel, Phys. Rev. 70 (1946) 965–971 and Rev. Mod. Phys. 21 (1949) 541–583], including for other ferroic systems, such as ferroelectrics and multiferroics. Kittel’s theory is revisited in this work, with a more detailed demonstration and emphasizing the main assumptions utilized, by using SI units instead of CGS units, as in the original Kittel’s works. The validity limits of the Kittel’s scaling law where the domain width varies with the square root of the sample thickness towards low thicknesses is derived, with the possibility of evolution towards large domains for ultralow thicknesses. Further, Kittel’s model is extended to the case where the sample has a non-vanishing net magnetization and it is shown how magnetization curves at zero temperature can be obtained. This is discussed by supposing constant width of a pair of neighboring domains with opposed magnetization, or by allowing this width to vary as function on the net magnetization of the sample. Though this latter assumption seems to be more reasonable from the point of view of the evolution towards a single domain state at saturation, it seems that the model able to yield most accurate vales of the coercive field is the domain with fixed width of the pair of domains, which justifies the assumption of „domain wall pinning”. The introduction of the demagnetization factor associated with the finite size of the film yields a maximum thickness up to which the films present hysteresis curves. The validity of this theory for ferrelectric domains is also briefly discussed.

Magneto-optical imaging of the domain wall distortions enhanced by magnetic fields in amorphous glass-coated microwire

Abstract: Here, we employ time-resolved magneto-optical Kerr system (MOKE) imaging to ascertain the origin of domain wall motion in microwires. The MOKE visualisations of the domain walls motion on the surface of the microwires prove the domain wall pinning and distortions tailored due to the perpendicular magnetic field. It is shown that domain wall pinning in a perpendicular field increases the domain wall tilting angle, which is in turn, related to the apparent domain wall velocity. The obtained result is important for correct interpretation of domain wall velocity measurements in microwires obtained by the Sixtus-Tonks method.

All optical writing and current-driven shifting of bits in ferrimagnetic strips: A micromagnetic study

Abstract: Nucleation of domains and domain walls by means of ultrashort laser pulses, and their current-driven shifting along a ferrimagnetic strip with high perpendicular magnetic anisotropy on top of a heavy metal, are both explored here by means of advanced micromagnetic modeling. Our results indicate that these systems are ideal candidates to develop high-density and high-efficient domain wall-based memory devices where the information is coded in series of bits in the form of perpendicular up and down domains flanked by chiral domain walls.

Multi-Domain versus Single-Domain: A Magnetic Field is Not a Must for Promoting Spin-Polarized Water Oxidation.

Abstract: The reaction kinetics of spin-polarized oxygen evolution reaction (OER) can be enhanced by ferromagnetic catalysts under an external magnetic field. However, applying a magnetic field necessitates additional energy consumption and creates design difficulties for electrolyzers. Here, we prove that a single-domain FM catalyst without external magnetic fields exhibits a similar OER increment to its magnetized multi-domain one. The evidence is given by comparing the pH-dependent increment of OER on multi- and single-domain FM catalysts with or without a magnetic field. The intrinsic activity of a single-domain catalyst is higher than that of a multi-domain counterpart. The latter can be promoted to approach the former by the magnetization effect. Reducing the FM catalyst size into the single-domain region, the spin-polarized OER performance can be achieved without a magnetic field, illustrating an external magnetic field is not a requirement to reap the benefits of magnetic catalysts.

Direct observation of tensile-strain-induced nanoscale magnetic hardening

Abstract: Magnetoelasticity is the bond between magnetism and mechanics, but the intricate mechanisms via which magnetic states change due to mechanical strain remain poorly understood. Here, we provide direct nanoscale observations of how tensile strain modifies magnetic domains in a ferromagnetic Ni thin plate using in situ Fresnel defocus imaging, off-axis electron holography and a bimetallic deformation device. We present quantitative measurements of magnetic domain wall structure and its transformations as a function of strain. We observe the formation and dissociation of strain-induced periodic 180° magnetic domain walls perpendicular to the strain axis. The magnetization transformation exhibits stress-determined directional sensitivity and is reversible and tunable through the size of the nanostructure. In this work, we provide direct evidence for expressive and deterministic magnetic hardening in ferromagnetic nanostructures, while our experimental approach allows quantifiable local measurements of strain-induced changes in the magnetic states of nanomaterials.

One-dimensional dynamics of the domain boundary in a seven-layer ferromagnetic structure

Abstract: The dynamics of the domain boundary is considered using the example of a seven-layer ferromagnetic structure with three thin and four wide magnetic layers. The structure of the domain boundary is represented as a kink solution of the sine-Gordon equation. The equation of motion for magnetization was solved numerically using an explicit scheme. The discretization of the equation was carried out according to a standard five-point scheme of the "cross" type. The paper shows the features of the dynamics of the domain boundary in a multilayer magnetic system in the presence of thin magnetic layers with an increased value of the magnetic anisotropy constant. Thin layers with an increased value of the magnetic anisotropy constant compared to the homogeneous state represent potential barriers to the moving domain boundary. Thin layers with an increased magnitude of magnetic anisotropy compared to a homogeneous state represent potential barriers to a moving domain boundary. A diagram of possible scenarios of the dynamics of the domain boundary is constructed depending on the initial velocity of its movement and the distance between three thin magnetic layers. The maximum value of the kink velocity for reflection from all potential barriers, depending on their size, is obtained. With an increase in the height and width of the barrier, the value of such a threshold maximum reflection velocity of the domain boundary increases nonlinearly. With a sufficiently high barrier height, there is already an almost linear dependence on the width of this threshold velocity. With a slight increase in the speed of movement of the domain boundary, the kink can pass through the first barrier, but it is reflected from the second barrier. There is also a case of kink oscillation between the second and third potential barriers. Such fluctuations are clearly inharmonious. The dependence of the threshold velocity on the distance between the barriers is obtained. As the distance between the barriers increases, the threshold speed value tends to a value equal to the threshold speed for one barrier. In the work, the minimum value of the speed of the domain boundary of the passage of all layers, depending on the parameters of potential barriers, is obtained. It is also found that there is a critical distance separating the dynamics of the domain boundary into two regions with qualitatively different behavior of the system.

Tensile properties of ferromagnetic nanofilms on stretchable substrates: Links between multi-cracking and magnetic properties

Abstract: The influence of multi-cracking on the magnetic response of more (Co) or less (Ni78Fe22) magnetostrictive ferromagnetic nanofilms on flexible substrates has been studied by combining tensile tests with in situ magneto-optical Kerr effect magnetometry measurements, up to large strain (20%). The results show that the variations of the magnetic features are more significant in the elastic domain (before cracking), while they are slightly affected in the multi-cracking regime, linked to the fact that the stresses evolve relatively little in this regime. This results in a lesser modification of the magnetization curves of Ni78Fe22, which also means weak magnetostatic (dipolar) effects despite a very high crack density. This is very promising for the applicability of magnetic films in highly curved or stretched systems, especially using weakly magnetostrictive materials.

Permeability of clustered soft magnetic narrow strips controlled by a surface normal magnetic field

Abstract: A unique functionality was reported for a thin film soft magnetic strip having a certain angle of inclined magnetic anisotropy. It can switch magnetic domain by applying surface normal field with a certain distribution. The domain switches between single domain and multi-domain. Our previous study shows that this phenomenon appears even in case of adjacent configuration of the multiple narrow strips. In this report, magnetic permeability for alternating current (AC) was investigated. The result shows that the AC permeability changes drastically depending on the domain structure in the frequency range from 10 kHz to 13 MHz. This result leads to apply this phenomenon to a switched inductor working with low energy consumption or a sensor for detecting magnetic field distribution.

Controllable CVD Growth of 2D Cr5Te8 Nanosheets with Thickness-Dependent Magnetic Domains.

Abstract: As a unique 2D magnetic material with self-intercalated structure, Cr5Te8 exhibits many intriguing magnetic properties. While its ferromagnetism of Cr5Te8 has been previously reported, the research on its magnetic domain remains unexplored. Herein, we have successfully fabricated 2D Cr5Te8 nanosheets with controlled thickness and lateral size by chemical vapor deposition (CVD). Then magnetic property measurement system revealed Cr5Te8 nanosheets exhibiting intense out-of-plane ferromagnetism with a Curie temperature (TC) of 176 K. Significantly, we reported for the first time two magnetic domains: magnetic bubbles and thickness-dependent maze-like magnetic domains in our Cr5Te8 nanosheets by cryogenic magnetic force microscopy (MFM). The domain width of the maze-like magnetic domains increases rapidly with decreasing sample thickness; meanwhile, the domain contrast decreases. This indicates the dominant role of ferromagnetism shifts from dipolar interactions to magnetic anisotropy. Our research not only establishes a pathway for the controllable growth of 2D magnetic materials but also points toward novel avenues for regulating magnetic phases and methodically tuning domain characteristics.