Magnetic Domain Wall Motion Research Articles

Universality of stochasticity in magnetic domain-wall motion

We report an experimental observation on universality of stochasticity in magnetic domain-wall motion along ferromagnetic nanowires. The domain-wall arrival time exhibits stochasticity depending on the nanowire width and strength of external magnetic field. Strikingly, all of the measured stochasticity data collapse onto a single universal curve that is given by a function of the number of de-pinning events. Such stochasticity has been found to be saturated for nanowires thinner than about 200 nm, which is possibly attributed to the dimensionality transition from two to one dimension. These results provide essential information for operating and/or design of domain-wall mediated devices.

A spintronic memristor bridge synapse circuit and the application in memrisitive cellular automata

Spintronic memristor is a new nonlinear circuit element which has property of memory and similar synapse, and the memristive effect can be realized by the spin-torque-induced magnetization switching or the magnetic domain wall motion. In this paper, a simple and compact memristor bridge synapse circuit which is able to perform signed synaptic weighting was proposed. The synaptic model have the good matching features in the system and is verified by matlab simulation experiment on the cellular automata, so this memristor synapse circuit is expected to be applied to neuromorphic system such as cellular neural network.

Magnetic domain wall motion in notch patterned permalloy nanowire devices

We report a study of magnetization reversal process of notch-patterned permalloy (Py) nanowires (NWs) by using an in-situ magnetic force microscopy (MFM). Three neighboring straight NWs and an individual straight NW with discs connected to the wires ends are fabricated by standard electron beam lithography through a lift-off technique. MFM images are taken in the presence of an in-plane magnetic field applied along the wires length. As a result, the nucleation, pinning and depinning of domain walls (DWs) along the NW are observed. The artificial constraints (notch) in such symmetrical geometry of NWs indeed serve as pinning sites to pin the DWs. The nature of magnetization reversal, pinning field and depinning field for the DWs that are observed in these permalloy NWs, indicate the key roles of notch depth, the terminal connection structure of NW end and the inter-wire interaction among the NWs. The in-situ MFM measurements are examined with the micromagnetic simulations. Consequently, good agreements are obtained for the DW structures and the effect of DWs pining/depinning, however a dissimilarity in experimental and simulation observations for the direction of propagation of DWs in NWs needs further investigation.

Magnetic bubblecade memory based on chiral domain walls.

Unidirectional motion of magnetic domain walls is the key concept underlying next-generation domain-wall-mediated memory and logic devices. Such motion has been achieved either by injecting large electric currents into nanowires or by employing domain-wall tension induced by sophisticated structural modulation. Herein, we demonstrate a new scheme without any current injection or structural modulation. This scheme utilizes the recently discovered chiral domain walls, which exhibit asymmetry in their speed with respect to magnetic fields. Because of this asymmetry, an alternating magnetic field results in the coherent motion of the domain walls in one direction. Such coherent unidirectional motion is achieved even for an array of magnetic bubble domains, enabling the design of a new device prototype—magnetic bubblecade memory—with two-dimensional data-storage capability.

Pinning Loss Power Density in Superconductors

The pinning loss power density is theoretically derived based on the resistive energy dissipation when the flux lines are driven by the Lorentz force in a superconductor. The obtained loss power density does not depend on the viscosity or flow resistivity, but is proportional to the pinning force density only, and it possesses the nature of hysteresis loss, as commonly measured in experiments. These features are predicted by the critical state model, which was recently proved theoretically. The obtained pinning force density is consistent with the prediction of the coherent potential approximation theory, a kind of statistical summation theory, for flux pinning. Thus, the irreversible properties associated with the flux pinning can be comprehensively described by these flux pinning theories. The irreversible flux pinning in the superconductor is compared with similar irreversible phenomena such as the motion of magnetic domain walls in ferromagnetic materials and the friction in mechanical systems. The po...

In-plane field-driven crossover in the spin-torque mechanism acting on magnetic domain walls in Co/Ni

We investigate the in-plane field dependence of current-induced magnetic domain wall motion in asymmetric Co/Ni nanowires. The application of an in-plane field changed the direction of domain wall motion. In a systematic study, by varying the magnetic layer thickness, we show that the in-plane field induces a crossover from spin Hall torque to adiabatic spin-transfer torque for the magnetic domain wall motion. Furthermore, the dependence of the threshold current density on the in-plane longitudinal field provides a way for determining the strength of the Dzyaloshinskii-Moriya interaction.

Temperature dependence of current-induced magnetic domain wall motion in an asymmetric Co/Ni nanowire

We have investigated the temperature dependence of current-induced magnetic domain wall (DW) motion in a Co/Ni nanowire, where the spin Hall torque is responsible for the DW motion. The threshold current density (Jth) for DW motion is found to be dependent on the temperature T and the depinning magnetic field Hdep, which is different from the symmetric Co/Ni system where Jth is insensitive to T and Hdep. This result indicates that an extrinsic pinning governs the DW motion when it is driven by the spin Hall torque. Our work therefore suggests that reducing the extrinsic pinning is a key for achieving a low-power-consumption device.

Reversible Electric-Field-Driven Magnetic Domain-Wall Motion

Control of magnetic domain-wall motion by electric fields has recently attracted scientific attention because of its potential for magnetic logic and memory devices. Here, we report on a new driving mechanism that allows for magnetic domain-wall motion in an applied electric field without the concurrent use of a magnetic field or spin-polarized electric current. The mechanism is based on elastic coupling between magnetic and ferroelectric domain walls in multiferroic heterostructures. Pure electric-field-driven magnetic domain-wall motion is demonstrated for epitaxial Fe films on BaTiO3 with in-plane and out-of-plane polarized domains. In this system, magnetic domain-wall motion is fully reversible and the velocity of the walls varies exponentially as a function of out-of-plane electric-field strength.Received 22 August 2014DOI:https://doi.org/10.1103/PhysRevX.5.011010This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society

Investigation of domain wall motion in RE-TM magnetic wire towards a current driven memory and logic

Current driven magnetic domain wall (DW) motions of ferri-magnetic TbFeCo wires have been investigated. In the case of a Si substrate, the critical current density (Jc) of DW motion was successfully reduced to 3×106A/cm2. Moreover, by using a polycarbonate (PC) substrate with a molding groove of 600nm width, the Jc was decreased to 6×105A/cm2. In order to fabricate a logic in memory, a current driven spin logics (AND, OR, NOT) have been proposed and successfully demonstrated under the condition of low Jc. These results indicate that TbFeCo nanowire is an excellent candidate for next generation power saving memory and logic.

Analytical Modelling of Magnetic DW Motion

The main analytical model for describing the motion of magnetic domain walls is the 1-D model formulated based on the profile of a Bloch wall. This model qualitatively describes the motion of magnetic domain wall in nanowires, while it may fail to match experimental and numerical results quantitatively. In recent years, the 1-D model has been further generalized by the introduction of terms such as spin transfer torques and spin orbit torques. It has also been used to describe the motion of different domain walls, including vortex walls. It seems that in many such attempts, formalisms are not followed accurately and the main assumptions of the model (such as the Bloch wall profile used in developing the model) are underestimated. In this paper, we first derive an analytical model to describe the motion of a tilting Bloch wall in perpendicularly magnetized materials using four collective coordinates. We then compare the energy landscape predicted by this model to that of micromagnetic simulations, highlighting the possibility of using such comparisons to develop corrections for the 1-D model.

Correlation between Martensitic Phase Transformation and Magnetic Barkhausen Noise of AISI 304 Steel

The movement of magnetic domain walls can be disturbed by material defects, also named pinning sites. When the magnetic field is changing, the domain walls move by “jumps” over these pinning sites. These jumps produce the so named magnetic Barkhausen noise (MBN). During walls movements also low amplitude and high frequency elastic waves are generated, they are called magnetic acoustic emission (MAE). Both MBN and MAE are technological and efficient alternatives of low cost in the study of ferromagnetic materials which suffer degradation by plastic deformation, presence of inclusions, different stresses configurations, etc., depending on their micro structural characteristics. For austenitic metastable stainless steel (no magnetic), plastic deformation induces martensitic phase transformation (ferromagnetic). The aim of this work is to correlate the MBN with the plastic deformation and martensitic phase transformation of AISI 304 stainless steel. Standard test samples were submitted to uniaxial tensile strength with different load schedules up to rupture. At every instant the MBN produced was registered. Then MBN was correlated with the steel microstructure when the martensitic phase was growing.

Magnetic Barkhausen Noise and Magneto Acoustic Emission in Stainless Steel Plates

When a slowly variable magnetic field (∼ Hz) is applied through a yoke on a ferromagnetic material, discontinuous changes on the magnetic flow density are produced. This phenomenon, called Magnetic Barkhausen Noise (MBN), obeys the movement of magnetic domain walls and its frequency range is about [10–100] kHz. It involves sudden magnetization changes and localized variations of mechanical stresses which originate elastic waves known as Magneto Acoustic Emission (MAE) on the frequency range of 20kHz up to 1MHz. Both, MBN and MAE depend on the material microstructural characteristics and they may be considered as non-destructive evaluation techniques. This work is based on MBN and MAE tests carried out on 5 groups of different stainless steel specimens (AISI 409, AISI 430, AISI 439, AISI 441A and AISI 444), for two applied magnetic fields, parallel and perpendicular to the rolling direction.

Observations of Magnetic Domain Structure Change in Nd2Fe14B Magnets at Elevated Temperature with External Magnetic Field by Lorentz Microscopy

ABSTRACTIn this study, we conducted the in-situ observations of the magnetic domain structure change in Nd2Fe14B magnets at elevated temperature by transmission electron microscopy (TEM) / Lorentz microscopy. The in-situ observations in Nd2Fe14B magnets revealed that the magnetization reversal easily occurred at the elevated temperature. At more than 180°C, the magnetic domain wall motion could be observed by applying the magnetic field of less than 20 mT. The motion of the magnetic domain wall was discontinuous and the domain wall jumped to one grain boundary to the neighboring grain boundary at 180°C. On the other hand, the continuous domain wall motion within grain interior as well as discontinuous domain wall motion was observed at 225°C, and some grain boundaries showed still strong pinning effect even at 225°C. The temperature dependence of the pinning effect of grain boundaries would not uniform.

Field and Current Driven Magnetic Domain Wall Motion in Disordered A1-FePt Nanowires

Arc-shaped magnetic FePt nanowires (10nm thick, 375nm wide) displaying in-plane anisotropy were fabricated. A vortex domain wall was formed in the middle of the arc after in-plane saturation in a field perpendicular to the wire. Translational domain wall propagation was observed at a field of 40 Oe applied parallel to the wire, while complete propagation to the end of the arc occurred at 100 Oe. Domain wall displacement at low velocity was achieved by current pulses of 2.5 1011 A m2 at zero applied magnetic field, comparable to the zero-field threshold current density of Permalloy. A field-assisted spin transfer torque drove the domain wall 1.8m to the end of the arc.

Magnetic domain-wall motion twisted by nanoscale probe-induced spin transfer

A method for deterministic control of magnetism using an electrical stimulus is highly desired for the new generation of magnetoelectronic devices. Much effort has been focused on magnetic domain-wall (DW) motion manipulated by a successive injection of spin-polarized current into a magnetic nanostructure. However, an integrant high-threshold current density of ${10}^{11}\ensuremath{\sim}{10}^{12}\phantom{\rule{0.16em}{0ex}}\mathrm{A}/{\mathrm{m}}^{2}$ inhibits the integration with low-energy-cost technology. Here, we report an approach to manipulate a single magnetic domain wall with a perpendicular anisotropy in a manganite/dielectric/metal capacitor using a probe-induced spin displacement. A spin-transfer torque (STT) occurs in the strongly correlated manganite film during the spin injection into the capacitor from the nanoscale magnetized tip with an ultralow voltage of 0.1 V, where a lower bound of the estimated threshold spin-polarized current density is $\ensuremath{\sim}{10}^{8}\phantom{\rule{0.16em}{0ex}}\mathrm{A}/{\mathrm{m}}^{2}$ at the tip/manganite interface. The dynamic of DW motions are analyzed using the Landau-Lifshitz-Gilbert method. This probe-voltage-controlled DW motion, at an ambient condition, demonstrates a critical framework for the fundamental understanding of the manipulation of the nanomagnet systems with low-energy consumption.

Modeling of Single Crystal Magnetostriction Based on Numerical Energy Relaxation Techniques

AbstractIn this work, an incremental energy minimization technique is proposed to simulate the magnetomechanically‐coupled, nonlinear, anisotropic and hysteretic response of single crystalline magnetic shape memory alloys (MSMA). The model captures the three key physical mechanisms that cause this characteristic behavior, namely the field‐ or stress‐induced martensite variant reorientation (twin boundary motion), magnetic domain wall motion, and local magnetization rotation, through an (incremental) energy minimizing evolution of internal state variables. Representative numerical response predictions are presented, compared to experimental observations, and discussed with respect to the associated microstructure evolution. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Micromagnetic Simulations of Magnetization Reversal in Misaligned Multigrain Magnets With Various Grain Boundary Properties Using Large-Scale Parallel Computing

This paper reports on micromagnetic simulations of the magnetization reversal behavior in polycrystalline Nd-Fe-B sintered magnets using large-scale parallel computing. A multigrain model is introduced to calculate the grain alignment dependence of the coercivity of polycrystalline Nd-Fe-B magnets with various magnetic characteristics at grain boundaries (GBs). The magnetic domain wall motion is accurately treated by dividing the analyzed object into extremely small elements. The multigrain model with a soft magnetic GB phase and a reverse domain at the initial state well reproduces experimental results. The calculations of coercivity with several GB widths are also carried out to seek for the origin of the sudden decrease of coercivity with nearly perfect grain alignment.

Theory of domain wall motion mediated magnetoelectric effects in a multiferroic composite

A model is discussed for magnetoelectric (ME) interactions originating from the motion of magnetic domain walls (DWs) in a multiferroic composite of orthoferrites $R{\mathrm{FeO}}_{3}$ $(R\text{FO}$) with magnetic stripe domains and a piezoelectric such as lead magnesium niobate-lead titanate (PMN-PT). The DWs in $R\text{FO}$ can be set in motion with an ac magnetic field up to a critical speed of 20 km/s, the highest for any magnetic system, leading to the excitation of bulk and shear magnetoacoustic waves. Thus, the ME coupling will arise from flexural deformation associated with DW motion (rather than the Joule magnetostriction mediated coupling under a static or quasistatic condition). A $c$ plane orthoferrite with a single N\'eel-type DW in the $bc$ plane and an ac magnetic field $H$ along the $c$ axis is assumed. The deflection in the bilayer due to DW motion is obtained when the DW velocity is a linear function $H$ and the resulting induced voltage across PMN-PT is estimated. It is shown that a combination of spatial and time harmonics of the bending deformation leads to (i) a linear ME coefficient defined by ${\ensuremath{\alpha}}_{E}=E/H$ and (ii) a quadratic ME coefficient ${\ensuremath{\alpha}}_{\mathrm{EQ}}=E/{H}^{2}$. The model is applied to yttrium orthoferrites (YFO) and a PMN-PT bilayer since YFO has one of the highest DW mobility amongst the orthoferrites. The coefficient ${\ensuremath{\alpha}}_{E}$ is dependent on the DW position, and it is maximum when the DW equilibrium position is at the center of the sample. In YFO/PMN-PT the estimated low-frequency ${\ensuremath{\alpha}}_{E}$ \ensuremath{\sim} 30 mV/cm Oe and resonance value is 1.5 V/(cm Oe). Since orthoferrites (and PMN-PT) are transparent in the visible region and have a large Faraday rotation, the DW dynamics and the ME coupling could be studied simultaneously. The theory discussed here is of interest for studies on ME coupling and for applications such as magnetically controlled electro-optic devices.

In-situ Lorentz microscopy of Fe85Si2B8P4Cu1 nanocrystalline soft magnetic alloys

Abstract Microstructure dependence of magnetic properties of soft magnetic Fe–Si–B–P–Cu nanocrystalline alloys were studied by using in-situ Lorentz microscopy in a transmission electron microscope equipped with a magnetizing system. In particular, we investigated in detail motion of magnetic domain walls in heat-treated Fe85Si12B6P4Cu1 amorphous ribbons. Smooth motion of domain walls was observed for the optimally heat-treated (at 430 °C) nano-crystalline alloy. Pinning of domain walls was observed for higher-temperature-heat-treated (470 °C) ribbons. Both ribbons showed a nanocrystalline structure containing α-Fe crystallites of about 15 nm in size. Electron diffraction patterns indicated that the higher-temperature-heat-treated samples contained boride precipitates, which is considered to cause less smooth domain wall motion.

Current-driven dynamics of coupled domain walls in a synthetic antiferromagnet

We develop the theory of magnetic domain wall motion in coupled double-layer systems where electrons can hop between the layers giving rise to an antiferromagnetic coupling. We demonstrate that the force from the interlayer coupling drives the walls and the effect of the extrinsic pinning is greatly reduced if the domain walls are initially separated. The threshold current density for metastable spin-aligned configurations is also much lower. We conclude that the interlayer coupling has a significant effect on domain wall mobility in double-layer systems.