Domain Wall Motion Research Articles

Investigation on the structure-optimized magnetic properties of hydrothermally synthesized SrBi2−X(CF)XNb2O9 multiferroic nanocomposites

Hydrothermally synthesized nano multiferroic SrBi2-X(CF)XNb2O9 (SBN-CF), (CF = CoFe2O4 & X = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) composite’s structure correlated magnetic attributes in view of reaction, exchange, and transport of ions have been comprehended from the perspective of electronic sector applications. The produced materials’ phase genesis, morphology, chemical composition, and magnetic characteristics were studied by XRD/Rietveld analysis, FEGSEM/EDS, FTIR, and VSM respectively. The Rietveld analysis of XRD data confirmed a single-phase orthorhombic structure of SBN. Further ferroelectric and cubic spinel structures of the ferrite phase have been noticed from the introduction of CF into the SBN host matrix. The crystallite size as computed (∼23–41 nm) from Debye Scherer’s formula was found to increase with dopant concentration. The imbibed morphological changes necessitated octahedral-shaped grains. The stoichiometric proportion with pronounced absorption bands is evident in EDS and FTIR studies. The impact of CF on SBN was unraveled at room temperature from the VSM study. The saturation magnetization was increased from 0.00 to 3.96 emu g−1, and the obtained coercivity values enhanced from 0.50 to 1400 Oe, due to the random fluctuations of the energy due to domain wall movements, interacting with the defective structure of the SBN material. The stress-induced distortion due to the variation in concentration of CF in SBN was configured from Y-K angles and increased from 33.55° to 61.49°. The high coercivity with a squareness value of less than 0.5 enunciates the genesis of a new class of materials for use in permanent magnet applications and memory devices.

Self-organized formation of domain arrays in TGS crystal by moving SPM tip

In this paper, we studied the formation of self-organized domain arrays created by moving biased tip of scanning probe microscope (SPM) in deuterated TGS crystals. The shape of created domains depends significantly on scanning direction and applied voltage. For scanning along c axis, the domain shape drastically changed from arrays to stripe domains at 150[Formula: see text]V. Scanning perpendicular to [Formula: see text] axis led to formation of the array of the dashed domains. Increasing of the dashed domain length leads to change of domain shape from arrays of dashed domains to solid stripe domain. The obtained effect has been considered in terms of the kinetic approach as a result of formation of comb-like domain with charged domain walls in the bulk due to repetitive appearance of the domain spikes. The spontaneous backswitching under the action of the depolarization field leads to the fast growth of the tooth to the surface and results in the transformation of the domain shape. The computer simulation of the nonuniform motion of charged domain wall under the action of depolarization field has been done. The obtained results demonstrate the essential role of screening processes and pave the way for further improvement of domain engineering methods.

Micromagnetic modeling of SOT-MRAM dynamics

We present a flexible and efficient approach to modeling the magnetization dynamics in modern SOT-MRAM cells, by coupling charge, spin, and magnetization dynamics in a three-dimensional framework. We expand on existing literature, to obtain spin current boundary conditions for modeling the Rashba-Edelstein effect. We compute the spin–orbit torques originating from both, the spin Hall and Rashba-Edelstein effect, and show that our model can reproduce experimental results for the thickness dependence of the spin torques in an Ir/CoFeB bilayer structure. Furthermore, we verify our approach by simulating magnetization reversal in field-free SOT-MRAM cells, and show that with the inclusion of the interfacial Dzyaloshinskii–Moriya interaction, we obtain domain wall motion similar to previously reported experimental results.

Influence of Ho spontaneous aggregation on the coercivity and magnetic domain movement of sintered NdY-Fe-B magnets

Development of NdY-Fe-B magnets not only reduces the cost of Nd-Fe-B type magnets but also promotes the balanced utilization of rare-earth resources. However, the lower coercivity of NdY-Fe-B magnets hinders their further development. This study investigated the coercivity of NdY-Fe-B magnets via intergranular doping of Ho76Al12Ga12 powders. Although this process improved the coercivity, the remanence substantially deteriorated with the increasing content of the Ho76Al12Ga12 alloy. A coercivity of 1.37 T was achieved in a NdY-Fe-B magnet with a Ho76Al12Ga12 alloy doping of 7 wt%, showing a coercivity increment (ΔHcj) of 0.64 T compared to the original magnet. This can be attributed to the observed microstructural and elemental distributions, as well as the analysis of the magnetic domain wall movement. An abnormal Ho-biased layer is observed between the Y-rich core and the Ho-rich shell in the matrix grains, exhibiting a higher anisotropy field compared than the shell layer. Further analysis revealed that the movement of magnetic domain wall movement was obstructed by the Ho-biased layer, demonstrating a domain-wall pinning effect within the matrix grains. Additionally, the formation of a Ho-rich shell in the outer area of the 2:14:1 matrix grain and the presence of a continuous uniform grain boundary phase were found to be important for improving both coercivity and thermal stability.

Microstructure and coercivity of Al-diffused Sm(Fe,Co,B)12 film

Fe-rich SmFe12-based compounds are considered as potential next generation permanent magnets due to their excellent intrinsic magnetic properties. However, their reported coercivities remain low, only ∼12 % of the magnetic anisotropy field of the SmFe12-based compound. In this work, we successfully increased the coercivity of B-doped Sm(Fe0.8Co0.2)12-based thin films from 1.1 T to 1.8 T by diffusion of Al into the grain boundaries. Detailed microstructural characterization using scanning transmission electron microscopy (STEM) and atom probe tomography (APT) revealed that the high coercivity is due to the segregation of Al into ∼4 nm thin B-rich amorphous intergranular phase, resulting in a reduction of its magnetization. This compositional modification of the intergranular phase can prevent the nucleation of reversed magnetic domains in the triple junctions and increase the pinning force of the grain boundary region against the magnetic domain wall motion. Based on detailed microstructural observations, the mechanism of coercivity enhancement is discussed.

Propagation dynamics of the Bloch-type domain wall on CoFeB nanostripes driven by a nanosecond magnetic pulse

Despite the abundance of research on the dynamics of magnetic domain walls (DW) on thin-film media, in-depth discussions regarding the behavior around the so-called Walker breakdown phenomenon are still scarce. In this work, propagation dynamics of the Bloch-type DW on CoFeB nanostripes with perpendicular anisotropy driven by a nanosecond magnetic pulse are investigated using micromagnetic simulation. It is found that on smaller nanostripes, the Walker breakdown corresponds with the oscillatory motion of the DW. On larger nanostripes, the formation of a Bloch-line with previously unreported behavior can be observed for magnetic pulses above HWB. Using a nanosecond field pulse instead of a continuous external field may allow for more direct control over the oscillatory DW motion and nucleation of the Bloch-line. A deeper understanding of the dynamics of the Bloch-type DW and its correlation to the applied nanosecond pulse may lead to better control of the DW for future spintronic devices.

Reduction of power loss in easy-plane FeSi soft magnetic composite under a weak bias magnetic field

This paper investigates the impact of a weak bias magnetic field (Hbias) along the easy magnetization plane direction on the power loss of easy-plane Fe-6.5 wt%Si (FeSi) soft magnetic composite (SMC). The results demonstrate that the power loss (Pcv) decreases by 18 % when the Hbias is 11.6 kA/m. Furthermore, it is found that the reduction in Pcv is not only attributed to decreases in hysteresis loss but also involves a decrease in excess loss. The causes of hysteresis loss and excess loss reduction are further investigated and it is found that the effect of the Hbias on the magnetization state plays an important role in the reduction of hysteresis loss. Additionally, the decrease in excess loss can be attributed to the reduction in local eddy current losses caused by non-uniform domain wall motion. These findings provide valuable insights for achieving high-frequency (MHz), high-efficiency, and miniaturized power electronic devices.

Extreme Domain Wall Speeds under Ultrafast Optical Excitation.

Time-resolved ultrafast EUV magnetic scattering was used to test a recent prediction of >10 km/s domain wall speeds by optically exciting a magnetic sample with a nanoscale labyrinthine domain pattern. Ultrafast distortion of the diffraction pattern was observed at markedly different timescales compared to the magnetization quenching. The diffraction pattern distortion shows a threshold dependence with laser fluence, not seen for magnetization quenching, consistent with a picture of domain wall motion with pinning sites. Supported by simulations, we show that a speed of ≈66 km/s for highly curved domain walls can explain the experimental data. While our data agree with the prediction of extreme, nonequilibrium wall speeds locally, it differs from the details of the theory, suggesting that additional mechanisms are required to fully understand these effects.

Local Control of a Single Nitrogen-Vacancy Center by Nanoscale Engineered Magnetic Domain Wall Motion.

Effective control and readout of qubits form the technical foundation of next-generation, transformative quantum information sciences and technologies. The nitrogen-vacancy (NV) center, an intrinsic three-level spin system, is naturally relevant in this context due to its excellent quantum coherence, high fidelity of operations, and remarkable functionality over a broad range of experimental conditions. It is an active contender for the development and implementation of cutting-edge quantum technologies. Here, we report magnetic domain wall motion driven local control and measurements of the NV spin properties. By engineering the local magnetic field environment of an NV center via nanoscale reconfigurable domain wall motion, we show that NV photoluminescence, spin level energies, and coherence time can be reliably controlled and correlated to the magneto-transport response of a magnetic device. Our results highlight the electrically tunable dipole interaction between NV centers and nanoscale magnetic structures, providing an attractive platform to realize interactive information transfer between spin qubits and nonvolatile magnetic memory in hybrid quantum spintronic systems.

Effect of ultralow Dy and Gd contents on surface crystallization and domain wall motion of FeCuSiBNbMo alloys

Surface crystallization of Fe-based melt-spun ribbons with high saturation induction leads to the formation of coarse grains after nanocrystallization, which results in a deterioration of the soft magnetic properties. Herein, doping with an ultralow concentration (0.1 at.%) of RE (RE = Dy and Gd) inhibits the surface crystallization of melt-spun FeCuSiBNbMo samples using industrial-grade Nb–Fe raw materials. This inhibition of surface crystallization promotes the formation of uniform and ultrafine nanograins after optimal annealing. Furthermore, the movement of domain wall is significantly affected by the presence of large grains (∼600 nm) in the free surface, which exerts a strong pinning effect on the domain wall motion. This pinning effect can be attributed to the higher magnetic anisotropy energy of the free surface compared to that of the nanocrystal region. The low coercivity observed in the samples with 0.1 at.% Dy and Gd addition is ascribed to the presence of dense and ultrafine nanocrystals, low effective magnetic anisotropy, and a weak pinning effect. This work provides insights into the relationship between surface crystallization, coercivity, domain wall motion, and magnetic anisotropy energy in Fe-based nanocrystalline ribbons.

Mechanical and magnetic properties of nonequiatomic Fe33Co28Ni28Ta5Al6 high entropy alloy by laser melting deposition

Soft-magnetic high-entropy alloy (HEA) Fe33Co28Ni28Ta5Al6 were prepared by laser-melting deposition (LMD). The microstructures and mechanical as well as magnetic properties of the fabricated samples were investigated. All samples comprised face- and body-centered cubic phases, where the proportion of the latter increased when the laser power was increased from 800 to 1400 W. With the increasing laser power, the yield strengths of the samples decreased slightly, and the saturation magnetization (BS) of the samples remained at approximately 1.07 T, the coercivity increased from 1034 A/m to 4456 A/m. The study showed that high laser powers resulted in high stress levels and increased the blocking effect on the motion of the magnetic domain walls of the samples. This work would provide a path way for the rapid manufacturing of high-performance soft-magnetic HEAs.

Spin Pumping by a Moving Domain Wall at the Interface of an Antiferromagnetic Insulator and a Two-Dimensional Metal

Spin Pumping by a Moving Domain Wall at the Interface of an Antiferromagnetic Insulator and a Two-Dimensional Metal

Universal Conductance Fluctuations in a MnBi2Te4 Thin Film.

Quantum coherence of electrons can produce striking behaviors in mesoscopic conductors. Although magnetic order can also strongly affect transport, the combination of coherence and magnetic order has been largely unexplored. Here, we examine quantum coherence-driven universal conductance fluctuations in the antiferromagnetic, canted antiferromagnetic, and ferromagnetic phases of a thin film of the topological material MnBi2Te4. In each magnetic phase, we extract a charge carrier phase coherence length of about 100 nm. The conductance magnetofingerprint is repeatable when sweeping applied magnetic field within one magnetic phase. Surprisingly, in the antiferromagnetic and canted antiferromagnetic phases, but not in the ferromagnetic phase, the magnetofingerprint depends on the direction of the field sweep. To explain our observations, we suggest that conductance fluctuation measurements are sensitive to the motion and nucleation of magnetic domain walls in MnBi2Te4.

Position error-free control of magnetic domain-wall devices via spin-orbit torque modulation

Magnetic domain-wall devices such as racetrack memory and domain-wall shift registers facilitate massive data storage as hard disk drives with low power portability as flash memory devices. The key issue to be addressed is how perfectly the domain-wall motion can be controlled without deformation, as it can replace the mechanical motion of hard disk drives. However, such domain-wall motion in real media is subject to the stochasticity of thermal agitation with quenched disorders, resulting in severe deformations with pinning and tilting. To sort out the problem, we propose and demonstrate a new concept of domain-wall control with a position error-free scheme. The primary idea involves spatial modulation of the spin-orbit torque along nanotrack devices, where the boundary of modulation possesses broken inversion symmetry. In this work, by showing the unidirectional motion of domain wall with position-error free manner, we provide an important missing piece in magnetic domain-wall device development.

Bend Induced Magnetic Bistability in Amorphous Microwires

ABSTRACT Magnetic and magneto-optical studies were carried out in microwires that had been subjected to the bending annealing. A previously unobserved effect of bending-annealing-induced magnetic bistability was discovered. This effect is observed only in the region of the sample subjected to bending. The length of the longitudinal region of the sample, in which the effect of induced bistability takes place, depended on the bending radius. In contrast to the classical version of this effect, bending-induced bistability was accompanied by the rapid movement of the longitudinal domain wall in the microwire surface.

Measurement of bearing capacity of steel road barrier flange via Barkhausen noise emission

This paper reports about the bearing capacity of a steel road barrier flange and its non-destructive assessment via magnetic Barkhausen noise. Bearing capacity was investigated as a function of the variable degree of plastic straining accumulated in the flange. Plastic deformation was developed on the samples cut from the flange and loaded by uniaxial tension under different strain rates in order to model the dynamic behaviour of plastic deformation during the real collisions. The results of experiments demonstrate that the accumulation of plastic deformation expressed in terms of increasing dislocation density, and the corresponding hardness of the matrix, reduces the bearing capacity of the flange expressed in terms of notch toughness. This decrease is only gentle for the lower plastic strain and becomes steeper for higher strains. Barkhausen noise emission also drops down and MBN envelopes are shifted to higher magnetic fields along with increasing plastic straining as a result of increasing opposition of increasing dislocation density against domain walls motion. It was also found that MBN parameters strongly correlate with notch toughness and especially magnetic hardness is very sensitive for determination of the flange state not only under the high strain rates but also under the strong dynamic impacts as those expected in the high angle collisions. The study proposes the methodology in which the used flanges could be approved for their further use.

Temperature dependence of dielectric nonlinearity of BaTiO3 ceramics

In many commercially utilized ferroelectric materials, the motion of domain walls is an important contributor to the functional dielectric and piezoelectric responses. This paper compares the temperature dependence of domain wall motion for BaTiO3 ceramics with different grain sizes, point defect concentrations, and formulations. The grain boundaries act as significant pinning points for domain wall motion such that fine-grained materials show smaller extrinsic contributions to the properties below the Curie temperature and lower residual ferroelectric contributions immediately above the Curie temperature. Oxygen vacancy point defects make a modest change in the extrinsic contributions of undoped BaTiO3 ceramics. In formulated BaTiO3, extrinsic contributions to the dielectric response were suppressed over a wide temperature range. It is believed this is due to a combination of reduced grain size, the existence of a core-shell microstructure, and a reduction in domain wall continuity over the grain boundaries.

Boosting domain wall velocity and stability in ferrimagnetic GdFe nanowires by applying laser-annealing process

This study highlights the significant achievement of enhancing domain wall (DW) velocity through the laser-annealing (LA) process in GdxFe100−x films, with a specific focus on the Gd26Fe74 composition. By investigating the current-induced DW motion, it was observed that the LA process on the edges and middle of the nanowires resulted in a remarkable improvement in DW velocity from around 600 m/s for non-laser-annealed to 1800 m/s for laser-annealed conditions. Furthermore, we conducted additional experiments to explore the stability and dynamics of a system involving DWs in a single wire. The experimental results revealed a stable and uniform movement of the DWs, as evidenced by a velocity of approximately 1800 m/s, even after the application of 20 pulses with a short pulse width of 1 ns. The resulting stability of the DW motion across a wide range of applied currents demonstrates the practical significance of the LA in achieving high-performance racetrack memories. Our findings suggest that the LA process has a similar effect on both the middle and edge treatments of the wire. This indicates that structural defects on the wire's edges are not the main cause of the observed low velocity or curvy shape of DWs. One possible mechanism for this effect is the reduction of the Ku value through the LA process. This study establishes a ground-breaking advancement by showcasing the effectiveness of the LA in enhancing DW motion velocity in GdFe ferrimagnetic thin films, thereby opening avenues for future research and industrial applications in this field.

Invariant polarization switching kinetics in an (Al0.8Sc0.2)N film with frequency and temperature

In this study, the switching kinetics in a (001)-out-of-plane-oriented (Al0.8Sc0.2)N thin film were systematically investigated as a function of temperature and frequency. The switching behavior followed the Kolmogorov–Avrami–Ishibashi model within the temperature and write-pulse width ranges of 300–473 K and 10 Hz–600 kHz, respectively. The switching speed increased linearly with the electric field, even at high electric fields. The frequency dependence of the coercive field (Ec) evaluated at room temperature revealed that the scaling regime of the domain-wall propagation did not transition to the flow regime, and the switching velocity of the domain increased linearly with the electric field even at high frequencies up to 600 kHz. The invariant domain-wall motion regime implies the potential of using (Al,Sc)N films for high-frequency applications. In addition, a formula for estimating the coercive field of an (Al,Sc)N film was derived by fitting the parameters obtained from the study of switching behavior. The formula indicated that the switching electric field tends to become insensitive to frequency as temperature increases. Moreover, the frequency dependency of the field was minimal even at room temperature. This is a useful index for estimating the drive voltage at the operating frequency and temperature.

Design of small volume and low power consumption logic gates based on 4-terminal multilevel magnetic cell

Spintronics is an emerging technology for designing logic circuits. The non-volatile logic based on the magnetic tunnel junction (MTJ) cell is a suitable solution to overcome the leakage power problem, which has become a major obstacle for CMOS technology. Here, we introduce a new style of magnetic gate (mGate) logic, which is built by a four-terminal cell. This cell operated by motion of domain wall that is based on spin transfer torque (STT) in a multi-level cell (MLC) structure. To reduce the complexity, a static circuit with a resistive load in ratioed logic style has been used. The use of MLC Gate logic in the static ratioed logic circuit is a suitable solution to reduce the complexity level of structure and power consumption in logic circuits in the field of spintronics. The performance of different magnetic logic gates have been investigated by simulations. The simulation results show that the MLC Gates offer a smaller area and lower power consumption and lower energy in comparison with the previous mGate and magnetic computing in memory.