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Field-driven magnetic domain wall propagation in ferromagnetic nanostrips with trapezoidal cross section has been systematically investigated by means of micromagnetic simulation. Asymmetric dynamic behaviors of domain wall, depending on the propagation direction, were observed under an external magnetic field. When the domain walls propagate in the opposite direction along the long axis of the nanostrip, the Walker breakdown fields as well as the average velocities are different. The asymmetric landscape of demagnetization energies, which arises from the trapezoidal geometry, is the main origin of the asymmetric propagation behavior. Furthermore, a trapezoid-cross-section nanostrip will become a nanotube if it is rolled artificially along its long axis, and thus a two-dimensional transverse domain wall will become a three-dimensional one. Interestingly, it is found that the asymmetric behaviors observed in two-dimensional nanostrips with trapezoidal cross section are similar with some dynamic properties occurring in three-dimensional nanotubes. [ABSTRACT FROM AUTHOR]

We have explored a fundamental phenomenon of magnetic domain wall collision in ferromagnetic nanowires using a micromagnetic simulation. With a systematic variation of an applied field strength, the domain wall collision phenomenon is observed around the Walker breakdown. Collision dynamics is found to mainly depend on domain wall inner structures. In the case of antiparallel transverse walls, it is found that the domain wall structure is preserved even after the collision, while parallel transverse walls experience multiple collisions with switching transverse components of colliding domain walls. After the Walker breakdown, collision of two domain walls comprises of creation and annihilation of a vortex and an antivortex. It is revealed that the collision dynamics of domain walls with an antivortex structure becomes strikingly distinctive depending on the relative direction of two colliding antivortex cores. Collision of vortex walls is observed to be associated with a complex interaction among vortex, antivortex, and even a tiny unreversed magnetic domain. [ABSTRACT FROM AUTHOR]

We have investigated dynamic behavior of a three-dimensional magnetic domain wall (DW) having a Bloch-point structure in a cylindrical ferromagnetic nanowire via micromagnetic simulations. We have found the existence of an onset depinning behavior of the Bloch-point domain wall (BP-DW) motion under external magnetic fields, which is originated from overcoming an intrinsic pinning barrier generated from spin configuration of the Bloch-point domain wall inner structure. Ultrafast sequential switching of Bloch-point spins is expected to have a single precessional motion with negligible ringing on a few picoseconds time scale, which might be attractive for future spintronic applications. [ABSTRACT FROM AUTHOR]

Ultrafast control of both electric and spin currents triggered by femtosecond laser pulse has attracted much attention due to future applications for broadband THz emitter as well as high‐speed spintronic devices. Optically generated spin current is converted to charge current via multiple spin‐charge conversion mechanisms, generating THz wave emission in magnetic multilayers. However, to date, quantitative and comparative investigation of THz emission originating from spin‐charge conversion mechanisms has not yet been fully explored. Here, direct and straightforward nondestructive probing to measure THz emission is provided at original Co/Pt and Co/Ta interfaces embedded in Pt/Co/Ta multilayers with polarization analysis of both optical pump and THz emission. These results allow a fundamental understanding of various spin‐charge conversion phenomena, which is a key basis for future spintronic THz source development. [ABSTRACT FROM AUTHOR]

We predict that the radial distance of a magnetic vortex core from the disk center shows a stepwise behavior during initial excited motion under an alternating-current magnetic field by means of micromagnetic simulations. The stepwise behavior is clearly observed around the resonance frequency and depends on the amplitude and frequency of the external magnetic field. It has been found that the stepwise behavior originates from the relative phase difference between the gyrovector and the radial distance of the vortex core. [ABSTRACT FROM AUTHOR]

We investigate a ratchet effect of magnetic domain wall motion in a ferromagnetic nanowire under AC magnetic fields using micromagnetic simulation. The ratchet effect for a transverse domain wall is achieved using an asymmetric magnetic potential generated by stray fields from non-contact trapezoidal ferromagnetic stubs near the straight nanowire. The ratchet phenomenon has been examined with various combinations of amplitude and frequency of the driving AC field. Interestingly, we find that the domain wall propagates along a preferential direction by the diode-like ratchet effect under AC field. The propagation of the domain wall strongly depends on the profile of the asymmetrical magnetic potentials and the driving AC field characteristics. [ABSTRACT FROM AUTHOR]

We investigated a forced oscillation motion of a magnetic vortex structure on a ferromagnetic nanodisk under an alternating-current (AC) external magnetic field using micromagnetic simulations. With variations of the AC field amplitude and the frequency, it has been revealed that the forced oscillation motion could become nonlinear and significantly deviated from the description of the original Thiele's equation. We propose a simple model with a dynamic correction of a gyrovector and a damping tensor in solving the Thiele's equation, which is valid even in case of the nonlinear magnetic vortex core motion. [ABSTRACT FROM AUTHOR]

We have explored a spontaneous domain wall motion in ferromagnetic nanowire at zero external magnetic field by means of micromagnetic simulation. Very interestingly, even with no external magnetic field, a spontaneous domain wall motion is observed with a speed about few tens of mis, which is significant and not negligible in analysis of the domain wall dynamics on nanowires. The spontaneous zero-field wall motion is explained based on the minimization condition of the magnetostatic energy, preferring to have a wire magnetically saturated. Average speed of the spontaneous wall motion is found to increase as the wire thickness increases. [ABSTRACT FROM AUTHOR]

We have investigated the ratchet effect of magnetic domain wall (DW) motion in a straight ferromagnetic nanowire under ac magnetic field by means of micromagnetic simulation. A structure-stable DW ratchet effect along the ferromagnetic nanowire is observed utilizing an asymmetric potential produced by a nonuniform magnetostatic stray field from an array of a periodic non-contact trapezoidal stubs. A diode-like consecutive operation process for a transverse DW motion is examined with variation of the ac field frequency and amplitude, where the necessary conditions for the DW ratchet effect are systematically examined. We have also obtained the empirical relation between a DW velocity of the ratchet effect and the ac field frequency and amplitude. [ABSTRACT FROM AUTHOR]

A three-dimensional breakdown behavior of the magnetic Bloch-point domain wall (BP-DW) propagation was investigated in a ferromagnetic nanowire with the variation of the external magnetic field by means of micromagnetic simulation. As magnetic field strength increases up to a threshold value, the BP-DW velocity approaches a critical phase velocity of the spontaneously emitting spin wave (SW), where a Cherenkov-type DW breakdown phenomenon is observed originating from an interaction between the spontaneously emitting SW and the BP-DW. It is found that the velocity of the BP-DW approaches a maximum value (∼2000 m/s) due to the intrinsic reversal time of a BP spin texture. This suggests that although cylindrical ferromagnetic nanowires might be free from the two-dimensional Walker breakdown phenomenon, there exists a Cherenkov-type three-dimensional breakdown behavior. [ABSTRACT FROM AUTHOR]

Time‐resolved magneto‐optical Kerr effect measurement is carried out to determine ultrafast hysteresis behavior during a photo‐induced demagnetization/remagnetization process for Co/Pt ferromagnetic multilayers. Due to the stroboscopic measurement scheme, hysteresis curve measured by a pump–probe technique exhibits an irreversible behavior, repeatedly reset to a metastable hysteresis state at each stroboscopic measurement, observed as the reduction of the coercivity. It is demonstrated that the stroboscopically measured hysteresis and the coercivity could be a stable parameter in describing the ultrafast photo‐induced spin dynamics for both reversible and irreversible behaviors. Moreover, it is found that an unusual coercivity behavior exists together with a nontrivial magnetization change under external fields comparable to the coercivity of the sample. [ABSTRACT FROM AUTHOR]

We investigate the dynamic behavior of the magnetic domain wall under perpendicular magnetic field pulses in flat ferromagnetic nanowires using micromagnetic simulations. It is found that the perpendicular magnetic field pulse can trigger the magnetic domain wall motion, where all the field torques are kept on the plane of nanowire strip. The speed of magnetic domain walls faster than several hundreds of meters per second is predicted without the Walker breakdown for the perpendicular magnetic driving field stronger than 200 mT. Interestingly, the dynamic behavior of the moving magnetic domain wall driven by perpendicular magnetic field pulses is explained by charging- and discharging-like behaviors of an electrical RC-circuit model, where the charging and the discharging of magnetic charges on the nanowire planes are considered. The concept of the RC-model-like dynamic characteristic of the magnetic domain wall might be promising for the applications in spintronic functional devices based on the magnetic domain wall motion. [ABSTRACT FROM AUTHOR]

In this paper, a magnon-bandgap controllable artificial domain wall waveguide is proposed by means of micromagnetic simulation. By the investigation of the propagation behavior and dispersion relationship of spin waves in artificial domain wall waveguides, it is found that the nonreciprocal propagation of spin waves in the artificial domain walls is mainly affected by the local effective exchange field, and the magnon bandgap can be controlled by changing the maximum value of the effective exchange field. In addition, it is observed that the artificial domain wall waveguides are structurally more stable than the natural domain wall waveguides under the same spin wave injection conditions, and the magnon bandgap of the artificial domain wall waveguides can be adjusted by its width and magnetic anisotropy parameters. The bandgap controllable artificial domain wall scheme is beneficial to the miniaturization and integration of magnon devices and can be applied to future magnonic technology as a high-pass filter with adjustable cutoff frequency. [ABSTRACT FROM AUTHOR]

Periodic injection behaviors of virtual magnetic domain wall (VDW) have been systematically investigated in asymmetrically shaped nanodot chains by means of micromagnetic simulations. Systematic investigation on a controllable VDW injection has been carried out. We demonstrate that precise control of VDW injection is achievable by using different nanodot shapes as well as by changing alternating magnetic field (AC field) profiles. The VDW position can be tuned by adjusting AC field frequency and amplitude. Field-controllable periodic VDW injection phenomenon is found to be sustainable over wide ranges of phase diagram spanned by AC field frequency and amplitude. [ABSTRACT FROM AUTHOR]

Seawater pumped storage power plants are one of the most important means of maintaining a stable operation of power systems in coastal areas. However, the development of seawater pumped storage power plants has been constrained by the extreme corrosiveness of seawater. The typical material of transmission pipes in these power plants is carbon steel due to its corrosion resistance and low cost. A magnetic field has an impact on corrosion. In this paper, the corrosion affection of carbon steel pipes in seawater under a magnetic field is investigated. The corrosion current and corrosion potential on the surface of carbon steel pipes under different magnetic fields are analyzed and compared through finite element model and electrochemical experiment. The results of the two methods are in excellent accordance, demonstrating that the direction and gradient of the magnetic field around carbon steel significantly impact corrosion behavior. The magnetic field perpendicular to the reaction surface of carbon steel promotes corrosion, and the influence of the magnetic field on corrosion is more significant with the increase of the magnetic field gradient. [ABSTRACT FROM AUTHOR]

We report a numerical study on the efficient and controllable suppression of the Walker breakdown along nanowires by positioning nanogaps with periodicity matching to that of transformational spin structure of the magnetic domain wall. While the Walker breakdown is suppressed, the transverse spin structure is found to be stably maintained without the formation of antivortex core throughout the propagation, shedding a light in faster spintronic devices based on the domain wall motion. [ABSTRACT FROM AUTHOR]

Fast in situ switching of magnetic vortex core in a ferromagnetic nanodisk assisted by a nanocavity, with diameter comparable to the dimension of a vortex core, is systematically investigated by changing the strength as well as the diameter of the effective circular region of the applied magnetic field. By applying a local magnetic field within a small area at the nanodisk center, fast switching time of about 35 ps is achieved with relatively low field strength (70 mT) which is beneficial for fast data reading and writing. The reason for this phenomenon is that the magnetic spins around the nanocavity is aligned along the cavity wall due to the shape anisotropy when the perpendicular field is applied, which deepens the dip around the vortex core, and thus facilitates the vortex core switching. [ABSTRACT FROM AUTHOR]

Abstract: With respect to the low-energy reaction and the Gamow-Teller (GT) resonant transition, the effect of electron screening on the β-decay rate in stellar interior is investigated. The analysis on the resonant transition is based on the shell model of nuclei. In particular, the effect of electron screening on the β-decay of on the 56C r is calculated as an illustration. It is shown that the electron screening increases the β-decay rate evidently at low temperatures and high densities. This may be an important factor in the studies of the stellar late-stage evolution and supernova bursts. [Copyright &y& Elsevier]

Here, the high-quality single crystal Ni2FeGa nanocrystallines with γ phase or L21 phase were successfully synthesized by using high-temperature hydrogen reduction method and adjusting the content of salt ions and the dynamic magnetic properties of them have been investigated. The expansion coefficient of L21 phase nanocrystallines was determined to be as high as 1.06×10−5 K−1 and the temperature-dependent damping factors be 0.0118 to 0.0234 in the temperature range 150–330 K. The results of dynamic magnetic properties revealed that the number of phonons increases with the temperature increase, which leads to the decrease of relaxation time τ and increase of the damping factor. Meanwhile, the temperature-dependent dynamic magnetic properties of L21 phase Ni2FeGa nanocrystallines showed that there is no obvious change in the effect of crystal field on the freezing of angular momentum of magnetic elements of Ni and Fe ions in the range of 100–300 K. Due to the easily adjustable shape, composition, and magnetization, the Ni–Fe–Ga nanoparticles have excellent microwave absorption properties in wide frequency range, which is a potential microwave absorption material. [ABSTRACT FROM AUTHOR]

The exchange stiffness coefficient, Aex, represents the strength of direct exchange interactions among neighboring spins. Aex is linked to most of the magnetic properties such as skyrmion formation, magnetic vortex, magnetic domain wall width, and exchange length. Hence, the quantification of Aex is essential to understanding fundamental magnetic properties, but little is known for the dynamics of Aex on a sub-picosecond timescale. We report the ultrafast dynamcis of Aex in an ordered magnetic state in Co/Pt ferromagnetic multilayer. Time-resolved magneto-optical Kerr effect and reflectivity measurements were analyzed for various pump fluences. We reveal that the significant dynamical reduction of Aex is responsible for the dramatic increase of remagnetization time for high fluences. The analysis shows that Aex dynamically varies, strongly affecting overall ultrafast demagnetization/remagnetization process. The investigation demonstrates the possibility of Aex engineering in femtosecond timescale and thereby provides a way to design ultrafast spintronic devices. The exchange stiffness coefficient describes the interaction between neighbouring spins of a ferromagnetic system and analysing these interactions at ultrafast timescales can reveal information on their demagnetisation and remagnetisation mechanisms. Here, the authors investigate the ultrafast dynamics of the exchange stiffness coefficient of a ferromagnetic multilayer system and model the data using a generalised three temperature model. [ABSTRACT FROM AUTHOR]

Understanding of ultrafast spin dynamics is crucial for future spintronic applications. In particular, the role of non-thermal electrons needs further investigation in order to gain a fundamental understanding of photoinduced demagnetization and remagnetization on a femtosecond time scale. We experimentally demonstrate that non-thermal electrons existing in the very early phase of the photoinduced demagnetization process play a key role in governing the overall ultrafast spin dynamics behavior. We simultaneously measured the time-resolved reflectivity (TR-R) and the magneto-optical Kerr effect (TR-MOKE) for a Co/Pt multilayer film. By using an extended three-temperature model (E3TM), the quantitative analysis, including non-thermal electron energy transfer into the subsystem (thermal electron, lattice, and spin), reveals that energy flow from non-thermal electrons plays a decisive role in determining the type I and II photoinduced spin dynamics behavior. Our finding proposes a new mechanism for understanding ultrafast remagnetization dynamics. [ABSTRACT FROM AUTHOR]

The dynamic behaviors of skyrmion in a nanofilm driven by spin waves have been numerically investigated by means of micromagnetic simulation. The results show that (i) the skyrmion shows a backward motion (towards the spin wave source) in the nanofilm with skyrmion Hall effect due to the spin wave scattering from the skyrmion; (ii) a fast (> 100 m/s) and periodic skyrmion motion can be achieved by introducing two spin wave sources to force the skyrmion move along the film edges; (iii) the velocity of the skyrmion motion depends on the amplitude and frequency of the driving magnetic fields as well as the nanofilm geometry, and the rotation sense of the skyrmion motion along the film edge depends on the topological number (Q = ± 1). The results might be a guidance for the design and development of future skyrmion-based devices in which skyrmions are used as information carriers. • We proposed a method to get a fast (∼ 100 m/s) and controllable skyrmion motion in nanofilm driven by spin waves. • Skyrmion Hall effect (SkHE) is regarded as an obstacle to skyrmion-based applications. In this work, instead of trying to suppress the SkHE, we take advantage of the SkHE, which eventually forces the skyrmion to move along the nanofilm edge. Modified by the nanofilm edge, a trajectory controllable and relatively fast skyrmion motion is obtained. [ABSTRACT FROM AUTHOR]

Highlights • The IrMn has ferromagnetic orders when SMR enhancement happens in the trilayers. • Temperature affects strongly the SMR of the trilayers. • Negative SMR at 50 K indicates spin-flop coupling could happen. Abstract Magnetic transport properties in Co 2 MnSn/IrMn/Pt trilayer structures have been investigated. Spin Hall magnetoresistance (SMR) enhancement in the trilayer structures has been observed, under the premise of exclusion current shunting effect. The experimental analysis indicates that the SMR enhancement may be closely related to the spin current enhancement reflected from the Co 2 MnSn/IrMn interface. Anomalous Hall resistance (AHR) study shows that its variation is quite similar to the SMR, suggesting that the SMR enhancement may also be closely related to spin-orbit coupled (SOC) scattering at the interface due to the coupling between IrMn and Co 2 MnSn layer. Temperature influences the SMR significantly in the trilayer structures at low IrMn thicknesses, which the IrMn has more ferromagnetic or ferrimagnetic orders than antiferromagnetic order. It indicates that the physical mechanism of the influencing of temperature on SMR of FM/AFI(AFM)/Pt trilayer structures need to be further investigated. The SMR changes its sign from positive to negative at temperatures lower than 50 K, revealing that spin-flop coupling between IrMn and Co 2 MnSn could happen at the interface. [ABSTRACT FROM AUTHOR]

In this work, we point out that the width and the nature of the magnetic phase transition, TC value, and as well as magnetocaloric effect in La0.7-xSmxCa0.3MnO3 compounds can be easily modified through Sm-doped into La-site. With an increasing Sm concentration, a systematic decrease in the magnetization, TC, and magnetic entropy change (ΔSm) are observed. The Arrott-plot proveds that the samples with x = 0 and 0.1 undergoing a first-order phase transition. Meanwhile, sample x = 0.2 undergoes a second-order phase transition, which exhibits a high value of the relative cooling power (81.5 J/kg at ΔH = 10 kOe). An analysis of the critical behavior based on the modified Arrott plots method has been done for sample x = 0.2. The results proved a coexistence of the long- and short-range interactions in La0.5Sm0.2Ca0.3MnO3 compound. [ABSTRACT FROM AUTHOR]

Co2FeGa-SiO2 nanocompounds were chemically synthesized by using SBA-15 as template, which has the L21 Heusler phase. The reactants comprised CoCl2 · 6H2O, Fe(NO3)3 · 9H2O and Ga(NO3) · xH2O with the addition of SBA-15 with different contents. The structure and morphology of the product were controlled by modulating the ratio of reactants to templates. After high-temperature annealing under H2 atmosphere and the removal of the template, the Co2FeGa nanowires, which are of about 125∼200 nm length, 4∼7 nm width and the length-to-width ratio of about 30 were observed by transmission electron microscope. The structure and component of the nanowires were confirmed by selected area electron diffraction, X-ray diffraction and energy-dispersive X-ray spectroscopy, respectively. The magnetic test showed that the saturation magnetization (Ms) was 87.5 emu/g for the Co2FeGa nanowires, and the Curie temperature was higher than 380K. The effective anisotropy constant Keff=4.196 × 105 J/m3 was calculated using magnetization curve, which is below the value of bulk Co2FeGa 6.54 × 105 J/m3. The dynamic magnetic properties study performed by ferromagnetic resonance indicated that the Gilbert damping coefficient α were about 0.1944-0.0288 for different samples. The high damping coefficient makes the nanocomposites promising to be used as a microwave absorber in the GHz band. [ABSTRACT FROM AUTHOR]

In this work, we present a detailed study on the magnetic properties and the magnetocaloric effect (MCE) of La 1−x K x MnO 3 compounds with x =0.05–0.2. Our results pointed out that the Curie temperature ( T C ) could be controlled easily from 213 to 306 K by increasing K-doping concentration ( x ) from 0.05 to 0.2. In the paramagnetic region, the inverse of the susceptibility can be analyzed by using the Curie-Weiss law, χ ( T )= C /( T − θ ). The results have proved an existence of ferromagnetic clusters at temperatures above T C . Based on Banerjee's criteria, we also pointed out that the samples are the second-order phase transition materials. Their magnetic entropy change was calculated by using the Maxwell relation and a phenomenological model. Interestingly, the samples with x =0.1–0.2 exhibit a large MCE in a range of 282–306 K, which are suitable for room-temperature magnetic refrigeration applications. The composites obtained from single phase samples ( x =0.1–0.2) exhibit the high relative cooling power values in a wide temperature range. From the viewpoint of the refrigerant capacity, the composites formed out of La 1−x K x MnO 3 will become more useful for magnetic refrigeration applications around room-temperature. [ABSTRACT FROM AUTHOR]

Influence of alkaline earth element doping in the A-site on the structure, magnetic and magnetocaloric properties of La 0.7 Ca 0.3-x A x MnO 3 (A = Sr and Ba; x = 0, 0.15 and 0.3) perovskite manganites have been investigated. X-ray diffraction data indicates that samples x = 0 and 0.15 crystallize in the orthorhombic structure (space group Pnma ), whereas samples x = 0.3 belong to the rhombohedral structure (space group R -3 c ). Substitution of Sr or Ba for Ca plays an important role in the increase of Curie temperature ( T C ) and modification the nature of the magnetic phase transition in materials. Sample x = 0 exhibits the first-order phase transition (FOPT) with a large magnetic entropy change (Δ S m ), whereas samples x = 0.15 and 0.3 exhibit the second-order phase transition (SOPT) characterizations and the moderate values of Δ S m . Using the modified Arrott plots method, the critical behaviors around T C for SOPT samples have been investigated through the values of critical parameters ( T C , β , γ , and δ ). We pointed out that Ba-doping favors establishing long-range ferromagnetic order, contrary to the case of Sr-doping. [ABSTRACT FROM AUTHOR]

In this paper, we present a detailed study on the critical behavior around the ferromagnetic (FM)–paramagnetic phase transition in La1−xKxMnO3 (LKMO) compounds with x = 0.05 - 0.20 . Our results pointed out the easiness in controlling the value of T_{C} from 212 to 306 K by increasing K-doping concentration (x) from 0.05 to 0.20. Analyzing temperature and magnetic field dependences of magnetization M(T, H) at temperatures around T_{C}$ reveals all the samples undergoing the second-order phase transition. Using the modified Arrott plots, the Kouvel–Fisher, and the critical isotherm analysis methods, we have found that the values of exponent $\beta $ in the range of 0.435–0.493, which deviate from the mean-field theory (MFT) for the long-range FM interactions, indicating a coexistence of short- and long-range FM orders. We also pointed out that the critical exponents ( $\beta $ and $\delta)$ depend strongly on K-concentration, shifting from values approaching those of the MFT ( $\beta = 0.5$ and $\delta = 3$ ) to values approaching those of the 3-D-Heisenberg model ( $\beta = 0.365$ and $\delta = 4.80$ ). In contrast, the value of the exponent $\gamma (=1.222 - 1.249)$ is almost independent of K-concentration. It suggests that K-doping favors establishing a short-range FM order in LKMO compounds. [ABSTRACT FROM AUTHOR]

• The industrial grade purity alloy exhibits RT magnetocaloric effect. • Ni doping broadens temperature span of magnetic entropy change around RT. • MAP provides a novel method for determining magnetic phase transition. For the widespread application of solid magnetic refrigeration technology, this is one of the key technologies to realize the wide temperature range of magnetic entropy change near room temperature. In this paper, the effect of Ni-doping on the magnetocaloric properties and the temperature range of magnetic entropy change was studied for La(Fe 0.94−x Ni x Co 0.06) 11.4 Si 1.6 B 0.25 alloy subjected to the industrial high-frequency suspension furnace. The results show that the Curie temperature of the alloy system can be adjusted to room temperature by changing the Ni content, and the temperature range of magnetic entropy change can be expanded effectively. In addition, the critical behavior of the industrial grade purity alloy system was evaluated by modified Arrott-plot and critical isotherm analysis methods, and the optimal values of critical parameters were obtained, providing a novel thermodynamic method to determine the critical behavior of magnetic phase transition in La(FeSi) 13 alloy system. [ABSTRACT FROM AUTHOR]

• The AFM THz spin wave is usually excited by a laser or a strong electrical current, which requires a high power. • In this work, we predict voltage-controlled THz magnon excitation associated with DW precession under an anisotropy gradient (d E a /d x). • This DW precession under d E a /d x is possible when the DW acceleration is negligible, which is different from the DW precession coupled with DW acceleration in previous investigations. • This work predicts the possibility for the excitation of THz magnons under a moderate voltage, which paves a way for developing ultrafast spintronic devices at a low power consumption. Exploring a low-power method for exciting terahertz (THz) signals is of great interest in developing devices with ultrafast signal processing. We numerically investigated the THz magnon excitation from a moving antiferromagnetic (AFM) domain wall (DW) driven by a voltage-induced magnetic anisotropy energy gradient (d E a /d x). This magnon excitation originates from the DW precession induced by d E a /d x. Unlike the AFM DW precession triggered by DW acceleration as predicted in previous investigation, the d E a /d x -induced DW precession is possible when the DW acceleration is negligible. When the frequency of DW precession is greater than the frequency gap of spin-wave propagation in the AFM medium, THz magnons are resonantly excited. Because d E a /d x can be generated under a moderate DC voltage, our work provides a potential approach for developing THz spintronic devices with a low power and dissipation. [ABSTRACT FROM AUTHOR]

The circulation reversal of magnetic vortex in ultra-small (sub-100 nm) ferromagnetic nanodots with a small off-centered hole is investigated. At zero applied field, the vortex state and the quasi uniform state are bi-stable in nanodisks. The existence of the small hole, which diameter is around the dimension of a vortex core, makes the vortex state in sub-100 nm magnetic nanomagnets is energetically more stable than uniform state. The results indicate perfect controllability of the circulation reversal using the in-plane magnetic field. We also reveal that the mechanism of the circulation reversal in sub-100 nm nanodisk is different from that in larger disk (a few hundreds nanometer to micrometer). It is paramount to control and manipulate the magnetic elements of dimension below 100 nm for their integration into nanoscopic spintronic and magnonic devices. [ABSTRACT FROM AUTHOR]

• The giant magnetocapacitance and negative capacitance in the MgO-based MTJ were observed, which indicates the important role of interface capacitance in the MTJ. • The anisotropy of capacitance was experimentally demonstrated and further explained well by the Debye-Frohlich model combined with the spin-tunneling-dependent carrier's relaxation behavior. The capacitance of magnetic tunnel junctions (MTJs) with the tunneling magnetocapacitance (TMC) effect has drawn lots of attention but there is still a lack of research on the capacitance anisotropy. In this work, a study of the capacitance in MgO-based MTJ is performed. The negative capacitance is observed and indicates the importance of interface capacitance in the MTJ. In further research, the interface capacitance depends on the relative orientation of magnetization in the two ferromagnetic layers (FMs), exhibiting a strong anisotropy. The Debye-Fröhlich model combined with the magnetization dependence of relaxation time is introduced to explain the behavior. Theory and experiment results of the relaxation time as a function of the relative angle of the two FM magnetizations are well fitted. It reveals that the TMC originates from the interface charge accumulation and spin-dependent tunneling. All the results suggest that the interface capacitance with apparent anisotropy plays an essential role in the TMC. [ABSTRACT FROM AUTHOR]

• We proposed a method to get a low-power-driven, unidirectional and ultrafast switching of magnetic vortex core under a continuous rotating magnetic field in a nanocavity mediated nanodisk. • The vortex core can be unidirectionally switched within 0.34, 0.47 and 0.86 ns under the excitation field with amplitude 4, 3 and 2 mT, respectively by choosing a proper value of the nanocavity's diameter and height. • Although the rotating magnetic field is applied, the amplitude of the core motion is very small, since the core is confined in the nanocavity. This is conducive to bit reading in magnetic data storage devices. Reliable unidirectional switching of magnetic vortex core driven by continuous rotating magnetic field is investigated using a permalloy nanodisk with a nanocavity inserted in the center in combination with micromagnetic simulations. It is reported that once the vortex core is confined in a nanocavity of diameter is comparable to the core size, the modes of the core motion (divergence/convergence modes) are modulated differently by the nanocavity: the threshold field amplitude required for vortex core switching is reduced for convergence mode, but not for divergence mode. We found that the confinement of the nanocavity to the core is mediated by the cavity height as well. Low-power-driven fast unidirectional switching is found to be achievable by carefully choosing the value of the nanocavity height. [ABSTRACT FROM AUTHOR]

• Interface antiferromagnetic coupling depends on Gd layer in Gd/CoFeTaB multilayer structure. • Interface antiferromagnetic coupling of multilayer structure can be enhanced by annealing. • Interface antiferromagnetic coupling affects magnetic and magnetoresistance properties of the system. By using the magnetron sputtering, a Gd/CoFeTaB multilayer structure film was fabricated, and investigated the effect of annealing temperature on magnetic and magnetoresistance characteristics of the multilayer film. A magnetic compensation phenomenon was observed, which means there is an antiferromagnetic coupling in the Gd/CoFeTaB system. It was found that the annealing enhances the antiferromagnetic coupling, lead to increase the Gilbert damping coefficient. Furthermore, an unsaturated magnetoresistance effect was observed, which is explained by the electron-electron interaction in the system. It is expected that the artificial antiferromagnetic multilayer system with weak macro-magnetism and internal magnetic order will has a good application prospect for the development of spintronics devices. [ABSTRACT FROM AUTHOR]

• A two-state model with high/low oxygen content is proposed in an amorphous system. • The two-state model can be explained magnetic and electrical properties of the CoFeTaBO film. • Based on the two-state model, the physical properties of amorphous systems can be predicted. Amorphous magnetic CoFeTaBO granular films with different oxygen contents are fabricated by using magnetron sputtering. The effect of oxygen contents on magnetic and electrical properties of the amorphous CoFeTaBO granular films are investigated, and a model for the coexistence of two states of oxygen-dependent metallic oxides in the CoFeTaBO film is proposed to explain magnetic and electrical characteristics in amorphous film system. It is expected that our proposed two-state model can provide a new perspective for understanding the physical properties of amorphous magnetic granular film materials. [ABSTRACT FROM AUTHOR]

We have investigated a diode-assisted GaAs based magnetoresistance (MR) effect at room temperature. It is found that the introduction of diode effectively enhanced the MR effect of the GaAs device, and the MR increases with increasing the length/width ratio of the device. The MR can be achieved to about 2600% at 1.2 T with a high MR sense ability of about 44% at 0.06 T and an extremely low energy consumption of sub-micro Watt. This work may open a new way for the practical application of the semiconductor based magnetic sensing industry. [ABSTRACT FROM AUTHOR]

• The magnetic vortex core can be periodically switched, modulated by the curvature. • The switching of magnetic vortex core can be achieved with small field amplitude (3 mT), wide frequency ranges (11–16 GHz), and fast switching time (200 ps). • Low-field ultra-fast switching of vortex core is proposed to realize the spintronic application. Periodic switching of magnetic vortex core driven by alternative magnetic field, applied perpendicularly, is investigated in a curved permalloy nanodisk by using micromagnetic simulation. Modulated by the curvature, the oscillations of the out-of-plane magnetization, caused by the external magnetic field, are confined in the center region, closed to the core, which reduces the threshold switching field down to 3 mT. While, the excitation of radial spin waves after a core switching dominates the reversal process generally in flat nanodisks, making it hard to control the final core polarity. The released spin waves in the center region during the core switching are relatively weak in curved nanodisk with most of radial spin waves dissipated to the thick edge part, resulting in a stable periodic vortex core switching. [ABSTRACT FROM AUTHOR]