Magnetization Reversal Process Research Articles

The effect of diameter on hysteresis loop squareness in iron nanowires array by micromagnetic simulation

Utilization of micromagnetic simulation is a very attractive subject to understand the magnetic behavior of nanowire arrays that tune their geometrical features and magnetic properties. Here, the micromagnetic simulations utilize to investigation of the single, and a 3 × 3 array of iron nanowires with diameters from 30 to 60 nm. The diameter size and the distance between the wires are selected according to the fabrication of iron nanowires grown in alumina templates. The simulation indicated that an increase in diameter led to a decrease in the coercive field and squareness ratio in both single nanowires and nanowire arrays. Besides, the simulation discloses that the magnetization reversal process of the nanowires with diameters more than 42 nm occurs through the nucleation and propagation of vortex domain walls. In the nanowires array, an increase in wire diameter increases the number of jumps in the hysteresis loop, indicating a more magnetic interaction between the nanowires.

Magnetoelectric effects in magnetic films with alternating magnetic anisotropy: the emergence and stability of Bloch points.

Magnetic topological states are a subject of intense investigation due to their potential for advancing scalable logic and information storage technologies. In this article, we investigate topological defects in magnetic films, focusing on Bloch point-like singularities in magnetization distribution with significant implications for magnetoelectric and ferroelectric properties. We explore exchange-coupled ferromagnetic films composed of alternating magnetic layers with distinct in-plane and out-of-plane magnetic anisotropy. Through micromagnetic simulations, we analyze the magnetization reversal processes and the emergence of Bloch point-like configurations induced by external magnetic fields. We identify the conditions necessary for stabilizing these states and elucidate their ferroelectric properties. Our study reveals that Bloch points act as sources of electrical charge due to the inhomogeneous distribution of magnetization, offering opportunities for implementing their electric properties in future devices.

Enhanced dipole-interaction in Nd-Dy-Fe-Co-B/Fe composite thick stacked trilayer

It is crucial to better understand the magnetization reversal process between soft and hard magnets and to achieve a high maximum energy product in thick composite multilayers. In this study, we find that the exchange interactions dominate in soft–hard-magnetic composite bilayers, while dipole interactions are predominant in soft–hard-magnetic composite trilayers. Based on the first-order reversal curve, magnetization reversal models are developed for both the thick composite bilayer and trilayer. Dipole interactions play an important role in the long range, resulting in higher coercivity and remanence in the thick trilayer. A multilayer in a stacked trilayer structure is achieved, which is composed of thick films with a perpendicular magnetic anisotropy at a thickness of up to 16 μm. The enhanced dipole interactions lead to a remanent polarization of 1 T and a maximum energy product of 22.5 MGOe. This work contributes to the preparation of thick films with a high maximum energy product for applications in magnetic microelectromechanical systems.

Recent Developments in Fe-Based Electrodeposited Thin Films

Electrodeposition is a commonly employed technique for synthesizing magnetic thin films, serving both fundamental research and practical applications. Of particular interest are Fe-based alloys like NixFe1-x and Fe1-xGax, as fundamental properties of ferromagnets as saturation magnetization (Msat), Curie temperature (TC), magnetic anisotropy (K) and magnetostriction constant (λ) strongly depend on the composition [1-2]. This work presents our latest findings on Fe-based thin films and multilayers, exploring diverse phenomena ranging from controlling magnetization switching in magnetoelastic structures to fine-tuning the out-of-plane (OOP) component of magnetization [3-4].Materials exhibiting moderate perpendicular magnetic anisotropy can develop stripe domains above a critical thickness (tcr). In addition to the interest in the basic understanding of this magnetic texture, nowadays, there is an increasing attention in this type of domains since they can be used for example for spin waves generation. The Ni80Fe20 alloy known as permalloy has been widely investigated because of its low coercivity and null magnetostriction. Sputtered Ni80Fe20 layers has been reported to have tcr around 300 nm [5], and its formation is generally believed to be due to columnar growth. However, for applications like magnetoimpedance, these stripes can be undesirable, hindering the growth of sufficiently thick layers to fabricate reliable sensors. Therefore, it is of interest the control of stripe domains in NixFe1-x films and whether the electrodeposition technique can also be used to tailor the appearance of this magnetic texture. Initially, we have examined the formation of stripe domains in the Ni90Fe10 alloy that is also of great interest because of its low coercivity and negative magnetrostriction (λ ~ -20 ppm). Subsequently, we have analyzed the magnetic behavior of electrodeposited NixFe1-x films in which the Fe content has been increased up to 30 at. %. Experimental results show that for Ni90Fe10 films magnetic stirring during growth suppresses the presence of stripes even for a thickness exceeding 1 µm. On the other hand, when growing with unstirred electrolyte, tcr can be reduced if a perpendicular magnetic field of 100 Oe is applied during samples growth. Eventually, it has been observed that tcr depends on the Fe content in the NixFe1-x and no stripes are observed for a content above 13 at.% when no perpendicular magnetic field is applied during growth.We have also investigated a bilayer structure comprised of two magnetic layers with opposite signs for the magnetostriction constant, Ni90Fe10 (λ ~ -20 ppm) and Fe70Ga30 (λ~ 70 ppm) to analyze the effect of magnetoelasticity on the magnetization reversal process. The exchange correlation length is a key parameter that determines the transition region between two opposite directions of the magnetization that depends on characteristics such as the magnetic anisotropy and the exchange stiffness constant. It is also used to quantify the domain wall thickness (δ) that can be considered as the distance over which the magnetic moments are correlated by exchange interactions, and that plays a fundamental role on magnetic systems relying on interfacial interactions as spring magnets or exchange-biased systems. Since the thickness of the layers cannot be higher than δ to avoid the magnetic switching of uncoupled regions, this implies that the thickness of layers is intrinsically limited in systems with interfacial coupling. We have studied Ni90Fe10/Fe70Ga30 bilayers with thicknesses exceeding δ to analyze the magnetic switching in these new magnetoelastic bilayer structures. 500 nm-thick Ni90Fe10 and Fe70Ga30 single layers have coercive fields of 22 Oe and 42 Oe, respectively, which guarantees that independent magnetic switchings from each layer can be experimentally observed.This has been confirmed by micromagnetic simulations performed by OOMF in which magnetoelasticity has not been included. However, when measuring the hysteresis loops of different NiFe/FeGa samples with thicknesses exceeding δ it is observed an in-unison magnetization reversal in all cases. Since magnetoelasticity is not an interfacial effect, it enables to control the magnetization reversal process of the whole bilayer regardless of the thickness being possible to promote this simultaneous reversal process regardless of the layer thickness (Fig.1).In conclusion, these results highlight the capability of electrodeposition to achieve new magnetic systems with enhanced functionalities.[1] J. M. D. Coey. Magnetism and Magnetic Materials. Cambridge University Press (2010)[2] Q. Xing, Y. Du, R. J. McQueeney, T. A. Lograsso. Acta Mater. 56 (2008) 4536−4546.[3] N. Coton, J. P. Andres, A. Cabrera, M. Maicas, R. Ranchal. J. Appl. Phys. 134 (2023) 103904.[4] N. Coton, J.P. Andres, E. Molina, M. Jaafar, R. Ranchal. J. Magn. Magn. Mater. 565 (2023) 170246.[5] M. Romera, R. Ranchal, D. Ciudad, M. Maicas, C. Aroca, J. Appl. Phys. 110 (2011) 083910 Figure 1

Role of (Pr20Nd80)60Tb15Cu15Ga10 intergranular addition on the magnetic properties of Nd-Fe-B sintered magnet

Intergranular addition using heavy rare earth (HRE) Dy/Tb containing alloys has been an effective way to modulate the microstructure and chemical distribution towards fabricating high-coercivity Nd-Fe-B sintered magnets. In this work, (Pr20Nd80)60Tb15Cu15Ga10 (at%) intergranular alloy powders were designed and introduced with dual purposes of forming Tb-rich matrix shell and antiferromagnetic RE6Fe13Ga grain boundary phase (GBP). With 3 wt% (Pr20Nd80)60Tb15Cu15Ga10 addition, the coercivity Hcj is significantly increased from 11.1 kOe to 17.9 kOe, accompanied with a high utilization efficiency of Tb (11.8 kOe/%) and a superior temperature coefficient of coercivity β(−0.531%/K). Microstructural analysis suggests that the improved wettability of grain boundary by (Pr20Nd80)60Tb15Cu15Ga10 addition is beneficial to form the Tb-rich matrix shell and antiferromagnetic RE6Fe13Ga GBP throughout the bulk magnets. Micromagnetic simulation is implemented to study the effect of formed ferromagnetic/antiferromagnetic GBP and Tb-rich matrix shell on the magnetization reversal process. Results show that the synergy of Tb-rich shell surrounding Nd/Pr-rich core and antiferromagnetic Nd/Pr-rich RE6Fe13Ga GBP is an effective way to promote the coercivity with high utilization efficiency of HRE Tb.

Hysteresis-loop phenomena in disordered ferromagnets with demagnetizing field and finite temperature.

Using numerical simulations, we investigate the impact of the demagnetization field and finite temperature on the hysteresis phenomena in disordered ferromagnetics systems. We model the behavior of thin systems employing the thermal nonequilibrium random field Ising model driven by a finite-driving rate protocol to study the shape of the hysteresis loop and demagnetization line and the magnetization fluctuations for varied parameters. Our results reveal a significant interplay of the disorder, the demagnetizing fields, and thermal fluctuations. In particular, at a fixed disorder and temperature, the increasing demagnetization coefficient gradually prologues the magnetization reversal process, altering the multifractal nature of the magnetization fluctuations. The process accompanies the appearance of extended linear segments in the hysteresis loop and changes in the demagnetization line while practically preserving the value of the coercive field and slightly changing the remanent magnetization. On the other hand, increasing temperature expands the system's response fluctuations and narrows the loop, affecting the coercive field and remanent magnetization. The interplay of thermal fluctuations and demagnetizing fields fully manifests in limiting the large-scale magnetization fluctuations, revealed by the multifractal spectra and the scaling functions of the avalanches. Our research offers new modeling perspectives with a more realistic scenario and provides insight into new hysteresis loop phenomena relevant to theoretical analysis and applications.

Long-term Variation of the Solar Polar Magnetic Fields at Different Latitudes

The polar magnetic fields of the Sun play an important role in governing solar activity and powering fast solar wind. However, because our view of the Sun is limited in the ecliptic plane, the polar regions remain largely uncharted. Using the high spatial resolution and polarimetric precision vector magnetograms observed by Hinode from 2012 to 2021, we investigate the long-term variation of the magnetic fields in polar caps at different latitudes. The Hinode magnetic measurements show that the polarity reversal processes in the north and south polar caps are non-simultaneous. The variation of the averaged radial magnetic flux density reveals that, in each polar cap, the polarity reversal is completed successively from the 70° latitude to the pole, reflecting a poleward magnetic flux migration therein. These results clarify the polar magnetic polarity reversal process at different latitudes.

Magnetization reversal process in flat and patterned exchange-biased CoO/[Co/Pd] thin films

Nanostructured magnetic materials have gained great interest due to their possible technological applications in electronic and spintronic devices or in medicine as drug carriers. The key issue which decides on their potential industrial utilization is an exhibited type of a magnetization reversal process. Two main approaches used to describe the switching mechanism are the domain wall motion and coherent magnetization rotation, known as the Kondorsky and Stoner–Wohlfarth models, respectively. The reversal modes can be distinguished by angular measurements of hysteresis loops; however, in many experimental reports the dependencies do not precisely follow either of the models. This makes the question of how the magnetization reversal takes place and how to control or modify it one of the unclear and worth investigation issues in the research on magnetic materials. In this paper, we present our studies on the magnetization reversal in the exchange-biased CoO/[Co/Pd] thin films deposited on a flat substrate and on an array of anodized titanium oxide nanostructures. We studied the reversal mechanism using hysteresis loops and First-Order Reversal Curves. Interestingly, instead of the typical for the flat Co/Pd multilayers Kondorsky process, the system shows a crossover between the domain wall motion and the coherent rotation. A similar situation takes place for the pattern sample. Here, we connect this unusual behavior with the interface exchange interaction responsible for the exchange bias effect.

Magnetization reversal phenomena in thin films presenting stripe domains

We present a study of the properties related to the magnetization reversal process in two thin-film samples with magnetic stripe domains: Fe0.82Ga0.18 (Fe–Ga) and Ni0.81Fe0.19 (permalloy). In Fe–Ga thin films, we focus on magnetization reversal driven by thermal activation by considering the magnetic viscosity behavior. The results suggest that the reversal process occurs gradually, where the magnetization switches direction via ∼10 nm-long jumps of the magnetic domain walls. On the other hand, vectorial hysteresis loops were performed in permalloy thin films with the aim to study the behavior of the transverse magnetization component (perpendicular to the applied field) during the magnetization reversal process. We show that the measurement of the transversal magnetization component shows a much higher sensitivity for the determination of the in-plane magnetic anisotropy than the usual hysteresis loops where the magnetization is parallel to the applied field. Moreover, this allows to highlight the competition between the intrinsic and rotatable anisotropies in thin films that present stripe domains.

Effect of growth conditions on magnetization reversal and magnetic anisotropy in Co2Fe0.5Ti0.5Si quaternary Heusler alloy thin films

Ferromagnetic resonance and magneto-optic Kerr effect (MOKE) techniques are employed to unravel the nature of ‘in-plane’ (IP) magnetic anisotropy and magnetization reversal (MR) processes in magnetron-sputtered 100 nm Co2Fe0.5Ti0.5Si (CFTS) thin films, deposited (and subsequently annealed) at different substrate temperatures (Ts) ranging from 200 °C to 550 °C. By varying TS, the CFTS films are produced with different amounts of anti-site (AS) atomic disorder. Irrespective of the degree of AS disorder, the IP uniaxial magnetic anisotropy (UMA) is prevalent in all the CFTS films. The TS450 and TS500 films, deposited at T S = 450 °C and 500 °C, stand out as they have (i) the least AS disorder, (ii) lowest value (α = 0.0055) of the Gilbert damping constant, (iii) high saturation magnetization ( ≅770 G ) at 300 K, (iv) UMA energy density as high as ≅1.6×104erg/cc at 120 K dropping to ≅1.0×104erg/cc at 300 K, (v) spin-wave stiffness ( D ) at T = 0 K, D0≅175 meVÅ2 and, as in other CFTS films, the electron–magnon interaction is primarily responsible for the thermal renormalization of D . Furthermore, in the TS450 and TS500 films, MOKE hysteresis loops at various angles ( ψH ) that the field makes with the easy axis in the film plane, reveals two mutually exclusive UMAs, UMA1≫UMA2 , with easy axes perpendicular to each other. By contrast, only a single UMA is observed in all the remaining films. When ψH=0∘ , MOKE domain images reveal that, consistent with the uniaxial nature of magnetic anisotropy, an abrupt reversal of magnetization is accompanied by the formation of 180° domains. When ψH = 90°, due to the presence of two UMAs in TS450 and TS500 films, following the field reversal, first the reverse domains nucleate and then grow at the expense of the fundamental domains through field-induced domain wall motion.

Magnetization reversal and stability of vortex state in convex shaped cylindrical nanodisks

Cylindrical nanodisks typically exhibit in-plane magnetization reversal comprising of nucleation and propagation of a vortex closure state. Present work investigates the magnetization reversal process in a cylindrical disk of radius ranging from 20 nm to 100 nm in which the flat surfaces at top and bottom are modified to convex shaped surfaces. It is found that the nucleation of vortex state no longer occurs as a result of this surface modification. Instead, a buckled magnetization state is nucleated which transforms to reverse buckled state yielding a square hysteresis loop. However, the out-of-plane hysteresis loop exhibits a vortex state at remanence. Analytical calculation of total free energy of both vortex as well as buckled state and the comparison thereof shows that the vortex state is ground state if radius of nanodisk is above 60 nm . Below this critical radius, buckled state is the ground state. But the non-appearance of vortex state at remanence in in-plane hysteresis loop of all of the nanodisks indicates a presence of energy barrier between vortex and buckled state. Height of the energy barrier is estimated using nudged elastic band method (NEBM) in all cases which proves that the energy barrier for vortex state weakens and the barrier for buckled state intensifies with the reduction of nanodisk size. At the critical radius of 60 nm , crossover of the two barrier heights occurs. Eventually, at the radius of 30 nm , the vortex state becomes totally unstable which can be toppled to buckled state with the slightest of perturbation.

Enhanced interlayer Dzyaloshinskii–Moriya interaction and field-free switching in magnetic trilayers with orthogonal magnetization

The indirect interlayer exchange coupling (IEC) between two magnetic layers holds significant importance in the field of spintronics and has been widely used in the construction of synthetic antiferromagnets. Recently, the interlayer Dzyaloshinskii–Moriya interaction (DMI), antisymmetric counterpart of IEC, has been discovered in magnetic trilayers with a heavy-metal spacer. In this study, we present an investigation on antisymmetric and symmetric counterparts of IEC in D022-Mn3Ga/Pt/Co trilayers with orthogonal magnetization. Due to the strong interlayer DMI across the entire multilayer, the symmetry of magnetic reversal process was broken, leading to an enhanced chiral exchange-bias field of 42.7 Oe in the Co layer. In addition, field-free spin–orbit torque (SOT) switching of D022-Mn3Ga layer has been realized in Hall bar devices. In-plane field dependence analysis of the SOT switching behavior reveals that the symmetric counterpart of IEC exhibits antiferromagnetic characteristics within the spacer thickness range of 2 nm ≤ tPt ≤5 nm. Moreover, the magnitude of both antisymmetric and symmetric counterparts of IEC exhibits an exponential decreasing trend with increasing tPt. These findings hold significant implications for the design and manipulation of three-dimensional chiral spin textures in the future spintronic devices.

Magnetization reversal phenomenon of higher-order lump and mixed interaction structures on periodic background in the (2+1)-dimensional Heisenberg ferromagnet spin equation

This paper mainly researches a useful model that can describe the rapid magnetization reversal process, namely the (2+1)-dimensional Heisenberg ferromagnet spin equation. Based on its Lax pair, we construct the iterative generalized (r,N−r)-fold Darboux transformation (DT), and obtain new position-controllable higher-order lump, periodic wave and rich mixed lump–breather interaction structures on periodic background. In particular, with the increase of N in the iterative generalized (r,N−r)-fold DT, we find that the structure of the lump and periodic wave can flip over with respect to the background. Moreover, we also find a bright lump structure with two peaks and two valleys, which does not flip with the increase of N. We study the magnetization trajectory and magnetization on the Bloch sphere, from which we discover that the magnetization is distributed in an incomplete unit sphere for the flipped case, while the magnetization is distributed in a complete unit sphere for the non-flipped case. These magnetization reversal phenomena are expected to have potential applications in understanding the rapid magnetization reversal process.

The influence of a copper spacer on the magnetic properties of Pd/Co/Cu/Pd multilayers with perpendicular anisotropy

The potential for technological applications of systems presenting perpendicular magnetic anisotropy is undeniable. With the advent of spintronics and the possibility to explore spin textures, such as skyrmions, in devices, it becomes fundamental to understand how to finely tune the magnetic properties of nanometric systems. In multilayered thin films, characteristics such as domain structure, saturation magnetization and perpendicular anisotropy may be tailored by modifying the interfaces. In the present study, the impact of a copper spacer of varying thickness on the magnetic properties of Pd/Co/Cu/Pd multilayers is investigated. The evolution of magnetization curves, domain patterns and magnetization reversal processes in terms of the spacers thickness are analyzed.

Investigation of magnetization dynamics in trilayer width-modulated nanowires

We have investigated the magnetization reversal processes and dynamic behavior of trilayered Py(50 nm)/Pd(tPd)/Py(20 nm) nanowires with periodic width modulation as a function of spacer layer thickness tPd in the range from 0 to 10 nm and compared them with single-layer nanowires. The ferromagnetic resonance spectra show more than three modes that result from a non-uniform demagnetizing field in width-modulated nanowires. We observe that the spacer layer thickness influenced the ferromagnetic resonance spectra, which showed different numbers and values of modes and frequencies due to the different magnetization configurations for different spacer layer thicknesses. We also found that the two ferromagnetic layers are exchange-coupled for tPd = 2 nm nanowire arrays, showing the sharp switching of magnetization from the static measurements and sharp frequency jump from 13.6 to 14.7 GHz around −18 mT from the dynamic measurements. However, for tPd = 10 nm, the two layers switch at different fields, indicating a gradual decrease in magnetization as the reversal is mediated through dipolar coupling. The origin of modes is well explained from the spatial mode profiles of top and bottom magnetic layers. The dynamic responses in this spin-valve-type structure are useful for designing microwave-based spintronic devices.

Direct observation of magnetic domain walls in glass-coated submicronic amorphous wires

Results on the magnetic domain walls in rapidly solidified magnetostrictive and non-magnetostrictive amorphous submicronic wires are reported. Utilizing Lorentz transmission electron microscopy (LTEM) for the first time in this context, we have visualized and analyzed the domain walls in such ultra-thin amorphous wires. All the investigated samples display vortex magnetic domain walls, regardless of wire composition or diameter. In non-magnetostrictive wires, the domain walls maintain their structure and symmetry under varying magnetic field conditions. In contrast, magnetostrictive wires show an elongation of their domain walls upon magnetic field application, a response linked to the magnetoelastic coupling between magnetostriction and internal stresses induced during wire preparation. This study advances the understanding of magnetization reversal processes in amorphous submicronic wires. The insights gained are crucial for future developments in miniaturized magnetic devices.

Defect manipulation for the coercivity enhancement of Nd-Fe-B permanent magnets

The demand for rare-earth based permanent magnets is expected to rise for various climate friendly technologies. This motivates for the search of better designed permanent magnets with optimal use of rare-earth elements without compromising the key magnetic properties. We simulate Nd2Fe14B based permanent magnets to study the effects of microstructure on coercivity (HC). We demonstrate a fast method to compute the microstructural parameters in numerical micromagnetics. We report a novel magnetic reversal process, which is primarily driven by defect thickness. By selective replacement of the defect with a hard magnetic phase HC is expected to rise by 1.5 times to that of single grain model with soft defect. This study is extended to a multigrain polycrystal model. Our systematic approach helps in identifying specific microstructural features pertinent for enhancement of coercivity. This work provides implications for future work to design improved defect engineered permanent magnets for green technologies.

Magnetization reversal via domain wall motion in vertical high-aspect-ratio nanopillar with two magnetic junctions

A vertical ferromagnetic (FM) nanopillar can be used as magnetic memory owing to characteristics such as its high storage capacity and high thermal stability. The perpendicular shape anisotropy (PSA) of the pillar enables its magnetization direction to be stabilized. A pillar with a high aspect ratio exhibits both strong PSA and magnetization with high thermal stability. Reversing the magnetization direction of such a pillar using the current flowing through it is a significant challenge in spintronics. However, spin injection from another FM layer alone cannot reverse the magnetization of pillars of which the length exceeds 100 nm. This motivated us to propose a magnetic junction (MJ) consisting of a high-aspect-ratio FM nanopillar with two thin FM layers. Using micromagnetic simulation, we demonstrate the magnetization reversal of a 150 nm-long pillar with a diameter of 15 nm. The simulation revealed that the magnetization of the pillar reverses because of the spin transfer torque induced by the spin injection from the two thin FM layers and the spin-polarized current (SPC) flowing in the pillar in the longitudinal direction. During the magnetization reversal process, a domain wall (DW) first forms at one end of the pillar due to the spin injection. Then, driven by the SPC, the DW moves to the other end of the pillar, and the magnetization is reversed. The magnetization direction of the pillar, controlled by changing the direction of the current flowing through the pillar, can be evaluated from the respective magnetoresistance values of the two MJs. Alternatively, by pinning the DW in the pillar, a three-value magnetic memory can be developed. In addition, multi-bit and analog memories can be developed by controlling the pinning position of the DW. The high-aspect-ratio pillar-writing scheme is foreseen to pave the way for the practical development of next-generation spintronic devices.

Analysis on coercivity enhancement mechanism of grain-boundary-diffused and Dual-alloyed Nd-Fe-B Magnets

With the rapid development of application fields, such as the green energy industry, has resulted in increased demand for magnetic characteristics, especially the coercivity (Hcj). In this paper, two types of (Nd, Dy)-Fe-B magnets with comparable Hcj values were prepared using by grain boundary diffusion (GBD) method and dual alloy (DA) method. The composition, microstructure, domain structure, and magnetization reversal process of GBD and DA magnets were subjected to comparison. Additionally, an analysis of the specific coercivity mechanism was also conducted by fitting the Brown's equation. The results of composition and microstructure analysis revealed the formation of core-shell structural grains were formed in both GBD and DA methods. Specifically, the GBD method exhibited a higher concentration of Dy in the shell, constituting 26.8 % of the total rare earth (RE) content. In contrast the DA magnets had Dy accounting for 15.8 % of the total RE content in the shell. This discrepancy was identified as the primary factor contributing to the superior efficiency in enhancing the coercivity (Hcj) observed in the GBD method. The fitting results showed that GBD magnets were more inclined to nucleate in the core region in grain, whereas DA magnets nucleate at the edge of the grain shell layer. Both the observation of magnetic domains and magnetization reversal processes analysis revealed that the demagnetization process in GBD magnets is more uniform, which leads to better squareness. Our finding can provide theoretical and experimental basis for the preparation of high-performance Nd-Fe-B magnets.

Pulsed magnetization reversal in Ni nanowire

Pulsed magnetic field-induced magnetization reversal in Ni nanowires is investigated using micromagnetic simulation. The pulse amplitude, duration, and size of the nanowire are proven to have substantial impacts on the magnetization reversal process. Increasing pulse amplitude and duration leads to faster magnetization reversal for 10 nm-diameter nanowires. But for 40 nm-diameter nanowires with the same aspect ratio, the pulse parameters have a complicated influence on the magnetization reversal process due to the formation and propagation of magnetic domain walls. Further investigations reveal that applying a pulsed field at a certain angle from the long axis of the nanowire or raising the temperature can significantly accelerate the magnetization reversal process.