Critical Switching Field Research Articles

Ultrafast switching dynamics of the ferroelectric order in stacking-engineered ferroelectrics

Recent research has highlighted the potential of ferroelectricity in van der Waals bilayers in providing an unconventional route for improving device performance. Understanding the static and dynamic properties of domain wall (DW) is critical unlocking this potential, as key parameters such as switching field and speed heavily rely on them. In this article, we conduct a theoretical exploration of the fundamental properties of textures in stacking-engineered ferroelectrics using a machine-learning potential model. Our results demonstrate that competition between the switching barrier of stable ferroelectric states and in-plane lattice distortion leads to a DW width of ten nanometers. We also demonstrate that DW motion can drastically reduce the critical ferroelectric switching field of a monodomain by two orders of magnitude and enable domain switching on a picosecond timescale, suggesting the potential for ultrafast and energy-saving non-volatile memory devices. Moreover, twisting the bilayer into a stacking Moiré structure results in a super-paraelectric state, because the ferroelectric order is reversibly broken by DW motion already at ultralow electric fields. These findings offer valuable insights into the behavior and properties of stacking-engineered ferroelectrics, with significant implications for the development of next-generation electronic devices.

Defect-induced monopole injection and manipulation in artificial spin ice

Lithographically defined arrays of nanomagnets are well placed for application in areas such as probabilistic computing or reconfigurable magnonics due to their emergent collective dynamics and writable magnetic order. Among them are artificial spin ice (ASI), which are arrays of binary in-plane macrospins exhibiting geometric frustration at the vertex interfaces. Macrospin flips in the arrays create topologically protected magnetic charges, or emergent monopoles, which are bound to an antimonopole to conserve charge. In the absence of controllable pinning, it is difficult to manipulate individual monopoles in the array without also influencing other monopole excitations or the counter-monopole charge. Here, we tailor the local magnetic order of a classic ASI lattice by introducing a ferromagnetic defect with shape anisotropy into the array. This creates monopole injection sites at nucleation fields below the critical lattice switching field. Once formed, the high energy monopoles are fixed to the defect site and may controllably propagate through the lattice under stimulation. Defect programing of bound monopoles within the array allows fine control of the pathways of inverted macrospins. Such control is a necessary prerequisite for the realization of functional devices, e. g. reconfigurable waveguide in nanomagnonic applications.

Achieving high energy storage performance of Pb(Lu1/2Nb1/2)O3 antiferroelectric ceramics via equivalent A-site engineering

Manipulating the critical switching field between antiferroelectric (AFE) state and ferroelectric (FE) is an important concept for tuning the energy storage performance of AFEs. As one of the lead-based AFE systems, Pb(Lu1/2Nb1/2)O3 promises high potential in the miniaturization of pulsed power capacitors, but the extremely high critical switching field and low induced saturated polarization demonstrate severe drawbacks with respect to temperature stability and flexibility. Here, A-site Ba2+ doping engineering is used to effectively reduce the critical switching field and improve the saturated polarization in BaxPb1-x(Lu1/2Nb1/2)O3 (0.01 ≤ x ≤ 0.08, abbreviated as xBa-PLN) ceramics. We found the AFE-FE phase transition can be occurred at 80ºC with a high energy storage density of 4.03 J/cm3 for Ba0.06Pb0.94(Lu1/2Nb1/2)O3 ceramic. Our results show that Ba2+ additions destroy the antiparallel structure of AFE phase, and finally reduce the critical switching field, demonstrating a potential alternative to modulate the energy storage performance of AFEs.

Field- and Current-Driven Magnetization Reversal and Dynamic Properties of CoFeB-MgO-Based Perpendicular Magnetic Tunnel Junctions* *Supported by the National Key Research and Development Program of China (Grant No. 2016YFA0300803), the Open Research Fund of Jiangsu Provincial Key Laboratory for Nanotechnology, the National Natural Science Foundation of China (Grant Nos. 11774150 and 11874135), and the Natural Science Foundation of Jiangsu Province of

We report a perpendicular magnetic tunnel junction (pMTJ) cell with a tunnel magnetoresistance (TMR) ratio of nearly 200% at room temperature based on CoFeB/Ta/CoFeB as the free layer (FL) and a synthetic antiferromagnetic (SAF) multilayer [Pt/Co]/Ru/[Pt/Co]/Ta/CoFeB as the reference layer (RL). The field-driven magnetization switching measurements show that the pMTJs exhibit an anomalous TMR hysteresis loop. The spin-polarized layer CoFeB of SAF-RL has a lower critical switching field than that of FL. The reason is related to the interlayer exchange coupling (IEC) through a moderately thick Ta spacer layer among SAF-RLs, which generates a moderate and negative bias magnetic field on CoFeB of RL. However, the IEC among RLs has a negligible influence on the current-driven magnetization switching of FL and its magnetization dynamics.

Electric field-induced phase transition and energy storage performance of highly-textured PbZrO3 antiferroelectric films with a deposition temperature dependence

Thin PbZrO3 (PZO) antiferroelectric films with (001)-preferred orientation were deposited on SrRuO3/Ca2Nb3O10-nanosheet/Si substrates using pulsed laser deposition. Variation of the deposition temperature was found to play a key role in the control of the microstructure and strongly influence the energy storage performance of the thin film. The critical phase switching field, where the aligned antiferroelectric (AFE) domains start to transform into the ferroelectric (FE) state, decreased with increasing temperature. On the other hand, the content of the FE phase in the AFE PZO thin films increased with increasing deposition temperature. A large recoverable energy-storage density of 16.8 J/cm3 and high energy-storage efficiency of 69.2% under an electric field of 1000 kV/cm were achieved in the films deposited at 525 °C. This performance was due to the high forward switching field and backward switching field values and the low difference between these two fields. Moreover, the PZO thin films showed great charge-discharge cycling life with fatigue-free performance up to 1010 cycles and good thermal stability from room temperature to 100 °C.

Thermal Stability and Critical Switching Field of Nanostructured Synthetic Ferrimagnets

In this study, the thermal stability and critical switching field of nanostructured elliptical synthetic ferrimagnets are calculated by using an analytical/numerical combined method, and the relationship between the two parameters is investigated. In conventional single magnetic layers, the critical switching field is a good measure of the thermal stability since the anisotropy, which determines the thermal stability, scales with the critical switching field. However, no such correlation is expected in nanostructured synthetic ferrimagnets, where the anisotropy is poorly defined owing to the strong interlayer magnetostatic interactions between two magnetic layers. This behavior is explained by the difference in the variation of the thermal stability with the external magnetic field as a function of the thickness asymmetry between two magnetic layers. The variation is found to be smaller at a smaller thickness asymmetry, where the interlayer magnetostatic coupling is stronger. This result indicates that the correlation between the two parameters is poorest in the completely symmetric synthetic ferrimagnet, but it increases with increasing thickness asymmetry of the synthetic ferrimagnets.

Concentration Phase Transition and Hysteresis Phenomena in Co-Nanofilms. Computer Data Processing and Simulation

The critical phenomena on cobalt monolayer films were studied by means of computersimulation. Proposed approach on the base of data of scanning tunneling microscopy gives possibilityestimate of critical concentration needed for concentration transition into ferromagnetic state. Assumptionabout presence of critical switching field allowed simulated hysteresis loops for given 1.5,2.0, 2.5 and 3.0 ML cobalt samples in frame of Ising model, which ones have qualitative agreementwith magnetometric data.

Angular dependence and temperature effect on switching field distribution of Co/Pd based bit patterned media

The motivation for this work is rooted in the reversal process that occurs in perpendicularly magnetic Co/Pd multilayered based bit-patterned media. In our work, temperature effect and angle dependence of critical fields (Hcr) and switching field distribution (SFD) are studied by both experiment and simulation. From our observation, when temperature increases from 77 to 300 K, the critical field of patterned area decreases from 13 to 11 kOe. Absolute SFD decreases from 2.6 to 2.2 kOe as thermal energy assists islands reversal. The relative SFD (SFD/Hcr) keeps constant with temperature. Although critical fields and absolute SFD vary with angles, relative SFD is independent of the field angle. The interactions between islands broaden relative SFD from 12% to 20% after considering dipolar interactions. The relative SFD by simulation agrees well with our experimental observation.

Zero-field magnetization reversal of two-body Stoner particles with dipolar interaction

We investigate magnetization reversal in a system of two Stoner particles with uniaxial anisotropies both subject to a static and antiparallel magnetic field, and taking into account their mutual dipolar interaction. We identify an interesting regime of stable synchronized magnetic dynamics where the two particles are implementing a single information bit. Here a modified Stoner-Wohlfarth limit occurs which results in a dramatically lower critical switching field Hc (including Hc=0) and also a substantially shorter reversal time. Our analytical results are verified by numerical simulations and offer new technological perspectives regarding devices for information storage and/or fast magnetic response.

Theoretical Limits on the Minimal Switching Field and the Switching Current in Magnetization Reversal

AbstractRecent theoretical limits of the minimal switching field and current for uniaxial magnetic nano-structures are reviewed. The results include also the optimal field and current pulses for the fastest magnetization reversal. Contrary to the general belief, the precessional magnetization reversal is not the fastest one, and its critical switching field is neither the lowest one.

Energy surface model and magnetization switching for exchange coupled magnetic particles

This paper describes the energy surface model for two exchange coupled magnetic particles and a study of the critical switching field in this coupled system. It is shown that for static switching, the total energy is continuously reduced during the reversal process. The critical switching fields versus applied field angle can be directly obtained from the energy surface model. The results are in good agreement with micromagnetic simulation. For a fast dynamic switching with small damping, the critical switching field may be further reduced. In addition, it is shown that an increase in either Ms or the grain volume of the soft particle will lead to a further reduction of the switching field. This is primarily due to an increase in the Zeeman energy that changes during the reversal.

Minimal field requirement in precessional magnetization switching

We investigate the minimal field strength in precessional magnetization switching using the Landau-Lifshitz-Gilbert equation in undercritically damped systems. It is shown that precessional switching occurs when localized trajectories in phase space become unlocalized upon application of field pulses. By studying the evolution of the phase space, we obtain the analytical expression of the critical switching field in the limit of small damping for a magnetic object with biaxial anisotropy in both the easy and hard plane. We also calculate the switching times for the zero damping situation by numerical means. We show that applying the field along the medium axis is good for both small field and fast switching times.

Coercivity and the critical switching field

The critical switching field and the coercivity of a material are not necessarily the same; these field values depend upon the magnetization process. Several field-related parameters are used to identify the major hysteresis loop of a material: the saturation field, remanent coercivity, critical field, average critical field, coercivity, median coercivity, and intrinsic coercivity. The parameters vary with changes in the magnetization process, which usually is assumed to be quasi-static. If the process is not quasi-static; i.e., it is faster or slower, the results of the process will change, and the field parameters will be different.

Biased switching of dipolar interacting nanoparticles in a periodic array

We study the switching behavior of a patterned cylinder array in terms of the Landau–Lifshitz–Gilbert equation, including the effect of applied magnetic field, shape anisotropy, crystalline anisotropy, and dipolar interaction between particles. The condition of uncorrelated switching is obtained when the strength of dipolar coupling varies. It shows that a high anisotropy is needed to overcome the strong dipolar interaction in order to ensure the uncorrelated switching. Under the condition of uncorrelated switching, the switching of a single magnetic moment is still much different from the switching of an isolated magnetic moment (without dipolar interaction). The distributions of the critical switching field and switching time of a single magnetic moment for the different configurations of magnetic moments are obtained. By applying a transverse bias field, both the large critical switching field and the switching time can be effectively reduced.

Magnetization reversal below the Stoner–Wohlfarth field

A novel concept of the critical switching field for the magnetization reversal of a single-domain particle with small damping constant in a field at an oblique angle to the easy axis is proposed. It is derived from the locus of the magnetization plotted on the contour map of the potential. The critical field is defined as the field in which the potential at the initial point is the same as that at the saddle point of the potential. The influence of the coordinate system on the critical field is also presented.

Flipping field and stability in anisotropic magnetoresistive sensors

Switched-capacitor flipping circuits developed for Philips KMZ51 and KMZ52 anisotropic magnetoresistance (AMR) sensors give up to 2.8 A/1 kHz current peaks. Such unusually high current deeply saturates the sensor and thus removes hysteresis, reduces noise, and increases the resistance against field shocks. These necessary strong flipping fields are predicted by the energetic model (EM), applied to the magnetization reversal in thin films. The EM parameters have been correlated to microscopic variables, revealing the field dependence of the speed of magnetization reversal. This is responsible for the value of the critical switching field (and therefore for the stability of the AMR sensor) in the easy axis directions, depending on the saturating field amplitude.

高周波記録に及ぼす媒体ダンピング定数αの影響

The influence of the damping constant α on recording characteristics at high frequencies was simulated by using the Langevin equation, with the condition that the head field rise time is constant. In the frequency range up to 190 MHz the signal outputs for α = 1 and α = 0.05 are same. On the other hand, in the higher- frequency range over 190 MHz, where the head field decreases before it reaches the maximum value, the signal outputs for α = 0.05 are larger than those for α =1.0. This is because the critical switching field depends on the damping constant α and it decreases with a lower value of α.

Analytical determination of the LLG zero-damping critical switching field

Previous numerical studies based on the Landau-Lifshitz-Gilbert (LLG) equation have considered the magnetization reversal of a uniaxial, single-domain particle due to an applied field pulse with a short rise time. When the LLG damping constant /spl alpha/<1, these studies have observed coherent switching for applied field magnitudes below the Stoner-Wohlfarth limit. The switching field computed in these studies decreases as /spl alpha//spl rarr/0, with apparent convergence to a limiting value. In this paper, analytic methods determine the value of the switching field in the zero-damping limit for an applied field pulse with zero rise time. The locus of normalized switching fields in parametric form is h/sub y/=-sin/spl theta/(cos/spl theta/-1)/2; h/sub z/=-cos/spl theta/(cos/spl theta/+1)/2; |/spl theta/|/spl les/2/spl pi//3. A non-parametric form is also derived. One surprising implication is that magnetization reversal may be caused by an applied field with easy axis component in the same direction as the initial magnetization (h/sub z/>0).

Electrical characteristics and threshold switching in amorphous semiconductors

The relative role of thermal and electronic effects on the threshold switching mechanism in the amorphous semiconductor Ge 17Te 79Sb 2S 2, has been investigated, using virgin sandwich type devices. Evidence is presented in support of a critical field bulk switching mechanism, in which secondary heating effects play a role only because of the variation of the critical switching field with temperature. Switching delay time measurements are interpreted in terms of adiabatic and steady state heating, for times shorter and longer, respectively, than the thermal time constant of the device. An isothermal switching field is calculated by correcting the measured switching field for the estimated change in temperature of the device prior to switching. Switching voltage measurements were made with pulse widths from 1 nsec. to d.c. In this range the isothermal switching field is independent of the pulse width. The d.c. switching field is shown to be a function of the thermal constraints of the device structure. In contrast, the isothermal switching field is a fundamental material parameter. It is established, from short pulse (1·5 nsec) measurements of the current voltage characteristic that the critical switching field marks the onset of a previously unreported high field conduction region. This characteristic, in the vicinity of the switching field, is similar to that of a reverse biased diode in the vicinity of its breakdown voltage.

Square‐Loop Ferrites for Logic Application

The effects of composition, post sintering, and operating temperature in a square‐loop ferrite system of interest for performing logic functions in digital telemetry applications are described. Ceramic processing methods used in preparing the multiaperture ferrite cores for this study are also described. Magnetic hysteresis loop characteristics of squareness ratio (Ra), magnetic induction switched (δBm), critical switching field (Hc, and maximum permeability (μm,) are reported as a function of zinc concentration in the system Mg0.5‐tMn0.8ZnxFe1.7O4abc. These characteristics are also investigated as a function of the post‐sintering treatments of air quenching and nitrogen annealing for the composition Mgo.35Zn0.15 Isel Essentially identical results are obtained for both the air‐quenching and the nitrogen‐annealing treatments. Significant hysteresis loop characteristics are shown at various operating temperatures in the range −78° to + 100°C.