Domain Nucleation Process Research Articles

Control of spin–orbit torque-driven domain nucleation through geometry in chirally coupled magnetic tracks

The interfacial Dzyaloshinskii–Moriya interaction (DMI) can be exploited in magnetic thin films to realize lateral chirally coupled systems, providing a way to couple different sections of a magnetic racetrack and realize interconnected networks of magnetic logic gates. Here, we systematically investigate the interplay between spin–orbit torques, chiral coupling, and the device design in domain wall racetracks. We show that the current-induced domain nucleation process can be tuned between single-domain nucleation and repeated nucleation of alternate domains by changing the orientation of an in-plane patterned magnetic region within an out-of-plane magnetic racetrack. Furthermore, by combining experiments and micromagnetic simulations, we show that the combination of damping-like and field-like spin–orbit torques with DMI results in selective domain wall injection in one of two arms of a Y-shaped device depending on the current density. Such an element constitutes the basis of domain wall based demultiplexer, which is essential for distributing a single input to any one of the multiple outputs in logic circuits. Our results provide input for the design of reliable and multifunctional domain wall circuits based on chirally coupled interfaces.

Tuning the Electro‐Optic Properties of BaTiO3 Epitaxial Thin Films via Buffer Layer‐Controlled Polarization Rotation Paths

AbstractBaTiO3 thin films emerge as a highly promising material platform for integrated photonics due to their outstanding electro‐optic properties and diverse functionalities. Despite extensive studies, there remains a notable gap in the understanding of the intricate relationship between the phase structure, domain switching kinetics and electro‐optic performance of these materials. By controlling the structural phase evolution, it is possible to gain deep insights into the physical mechanisms underlying the electro‐optic performance. Here, the phase constitution of BaTiO3 epitaxial thin films is successfully tuned by the insertion of a GdScO3 buffer layer. Continuous polarization rotation paths are observed from an out‐of‐plane tetragonal‐like phase, to an intermediate rhombohedral‐like phase, and finally an in‐plane tetragonal‐like phase, achieving an enhanced effective electro‐optic coefficient of 175 pm V−1 compared to unbuffered films. Furthermore, by in situ second harmonic generation microscopy and electro‐optic measurements, the domain switching behaviors in both statistical and spatially resolved manners are examined, resulting in a clear delineation of the key domain nucleation processes. The in‐depth explorations of these structural mechanisms and kinetics inform the rational design of strong electro‐optic thin films and help in the realization of high‐performance integrated photonic devices such as electro‐optic modulators and multilevel phase shifters.

Direct Imaging of Antiferromagnet‐Ferromagnet Phase Transition in van der Waals Antiferromagnet CrSBr

AbstractThe advent of van der Waals (vdW) ferromagnetic (FM) and antiferromagnetic (AFM) materials offers unprecedented opportunities for spintronics and magneto‐optic devices. Combining magnetic Kerr microscopy and density functional theory calculations, the AFM‐FM transition is investigated and a surprising abnormal magneto‐optic anisotropy in vdW CrSBr associated with different magnetic phases (FM, AFM, or paramagnetic state) is discovered. This unique magneto‐optic property leads to different anisotropic optical reflectivity from different magnetic states, permitting direct imaging of the AFM Néel vector orientation and the dynamic process of the AFM‐FM transition within a magnetic field. Using Kerr microscopy, not only the domain nucleation and propagation process is imaged but also the intermediate spin‐flop state in the AFM‐FM transition is identified. The unique magneto‐optic property and clear identification of the dynamics process of the AFM‐FM phase transition in CrSBr demonstrate the promise of vdW magnetic materials for future spintronic technology.

Magnetic-field-controlled growth of magnetoelastic phase domains in FeRh

Magnetic phase transition materials are relevant building blocks for developing green technologies such as magnetocaloric devices for solid-state refrigeration. Their integration into applications requires a good understanding and controllability of their properties at the micro- and nanoscale. Here, we present an optical microscopy study of the phase domains in FeRh across its antiferromagnetic–ferromagnetic phase transition. By tracking the phase-dependent optical reflectivity, we establish that phase domains have typical sizes of a few microns for relatively thick epitaxial films (200 nm), thus enabling visualization of domain nucleation, growth, and percolation processes in great detail. Phase domain growth preferentially occurs along the principal crystallographic axes of FeRh, which is a consequence of the elastic adaptation to both the substrate-induced stress and laterally heterogeneous strain distributions arising from the different unit cell volumes of the two coexisting phases. Furthermore, we demonstrate a magnetic-field-controlled directional growth of phase domains during both heating and cooling, which is predominantly linked to the local effect of magnetic dipolar fields created by the alignment of magnetic moments in the emerging (disappearing) FM phase fraction during heating (cooling). These findings highlight the importance of the magnetoelastic character of phase domains for enabling the local control of micro- and nanoscale phase separation patterns using magnetic fields or elastic stresses.

Direct visualization of percolating metal-insulator transition in V2O3 using scanning microwave impedance microscopy

Using the extensively studied V2O3 as a prototype system, we investigate the role of percolation in metal-insulator transition (MIT). We apply scanning microwave impedance microscopy to directly determine the metallic phase fraction p and relate it to the macroscopic conductance G, which shows a sudden jump when p reaches the percolation threshold. Interestingly, the conductance G exhibits a hysteretic behavior against suggesting two different percolating processes upon cooling and warming. Based on our image analysis and model simulation, we ascribe such hysteretic behavior to different domain nucleation and growth processes between cooling and warming, which is likely caused by the decoupled structural and electronic transitions in V2O3 during MIT. Our work provides a microscopic view of how the interplay of structural and electronic degrees of freedom affects MIT in strongly correlated systems.

Temperature-modulated magnetic skyrmion phases and transformations analysis from first-order reversal curve study

We performed a temperature-modulated first-order reversal curve (FORC) study on a Pt/Co/Fe/Ir magnetic stack that exhibited a magnetic phase transition from isolated skyrmions to skyrmion lattice with increasing temperature. Using in situ magneto-optical Kerr imaging, a generalized description of domain transformations associated with the FORC distribution peaks at both their reversal and sweeping field are derived to allow for direct analysis from the FORC diagram. The sweeping field of the peak, which is commonly ignored in analysis, is identified as the process of domain propagation or nucleation towards terminal domain separation. This process is found to be essential in inducing magnetization irreversibility to reveal domain transformations. In addition, a model characterized by the FORC distribution peaks was developed to describe the transition from the isolated skyrmion to skyrmion lattice phase as well as to identify important field ranges for the transformations. This study establishes an intuitive form of analysis for the otherwise abstract data of FORC distribution for the characterization of magnetic skyrmions in the active field of skyrmionics.

Hybrid Stochastic Fractal-Based Approach to Modeling the Switching Kinetics of Ferroelectrics in the Injection Mode

The paper is devoted to the development and implementation of a hybrid stochastic fractal-based approach for modeling electron-induced kinetics of polarization switching in ferroelectrics as the self-similar memory physical systems. The mathematical model of fractal dynamic system includes the initial value problem for the fractional order differential equation. Computational schemes for solving fractional differential problem are constructed using the Adams–Bashforth–Moulton type predictor-corrector methods. The stochastic algorithm based on the Monte Carlo method is proposed to simulate the domain nucleation process during restructuring the domain structure in ferroelectrics. The polarization switching current of ferroelectrics in the electron injection mode is evaluated to demonstrate the computational experiment results with a comparison of the experimental data.

Control of domain structure and magnetization reversal in thick Co/Pt multilayers

We present a study of the magnetic properties of ${[\mathrm{Co}(3.0\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/\mathrm{Pt}(0.6\phantom{\rule{0.16em}{0ex}}\mathrm{nm})]}_{N}$ multilayers as a function of Co/Pt bilayer repetitions N. Magnetometry investigation reveals that samples with $N\ensuremath{\ge}15$ exhibit two characteristic magnetization reversal mechanisms, giving rise to two different morphologies of the remanent domain pattern. For applied magnetic field angles near the in-plane field orientation, the magnetization reversal proceeds via a spontaneous instability of the uniform magnetic state resulting in perpendicular stripe domains. Conversely, for field angles close to the out-of-plane orientation, the reversal occurs via domain nucleation and propagation leading to a mazelike domain pattern at remanence. Our measurements further enable the characterization of the N-dependent energy balance between the magnetic anisotropy and magnetostatic energy contributions, revealing a gradual disappearance of the domain nucleation process during magnetization reversal for N 14. This leads to the exclusive occurrence of an instability reversal mechanism for all field orientations as well as alignedlike stripe domains at remanence. Furthermore, a detailed study of the influence of the magnetic history allows the determination of a range of material properties and magnetic field strengths, where a lattice of bubble domains with remarkably high density is stabilized. These modulations of the ferromagnetic order parameter are found to strongly depend on N, in terms of center-to-center bubble distance as well as of bubble diameter. Moreover, such Co/Pt multilayers could be utilized to engineer field reconfigurable bubble domain lattices, which resemble magnonic crystals.

Magnetothermodynamic Properties and Anomalous Magnetic Phase Transition in FeRh Nanowires

Thermal properties of submicrometer wires of Pd-doped FeRh alloys are evaluated from measurements of transport properties around the first-order antiferromagnetic to ferromagnetic phase transition. Recently, in a submicrometer wire of FeRh alloy, an asymmetric structure between heating and cooling processes was reported in the vicinity of the phase transition temperature. A system where finite-size effects appear is expected to show different magnetic and thermal properties from those in bulk and thin film. However, thermal or magnetization measurements are difficult to perform on samples with such a tiny volume. Here, we demonstrate a quantitative evaluation of thermal properties in thin films and submicrometer wires of B2-ordered Pd-doped FeRh alloy grown on MgO (001). Resistivity measurements on a series of wires with different widths reveal that the anomaly in the resistance change is enhanced in narrow wires. As the transport properties in submicrometer wires sensitively reflect those magnetic states, the entropy change and the irreversible energy loss during the first-order phase transition have been determined via resistance measurements. We find a larger energy loss in smaller samples where wider hysteresis loops appear in temperature-driven measurements. This method can be a probe to evaluate the finite-size effect induced by a restricted magnetic domain nucleation process during the phase transition.

Nanoscale probing of asymmetric magnetization reversal in perpendicularly exchange biased Pt/Co/Pt/IrMn multilayers

Abstract Asymmetric magnetization reversal in perpendicularly exchange biased Pt/Co/Pt/IrMn multilayers was studied in nanometer scale by non-contact magnetic force microscopy with variable highly localized bipolar magnetic fields of the MFM tip. The hysteresis process of domain nucleation and pinned domain wall motion has been triggered and mapped simultaneously through MFM. Unstable magnetization reversal of submicron domains has been directly observed as well as exchange bias induced asymmetry in the depinning fields for domain wall motion. The current results demonstrated a possible way to locally mapping and manipulating novel magnetic nano-structures such as vortices and Skyrmions.

Model for the correlation between magnetocrystalline energy and Barkhausen noise in ferromagnetic materials

In the present work a model for the correlation between magnetocrystalline anisotropy energy and Barkhausen noise is proposed. The link between the magnetocrystalline anisotropy energy and the magnetic Barkhausen noise is due to the influence of the crystallographic texture on the domain nucleation process which produces the Barkhausen signal in the branch from saturation to remanence. The statistical distributions of magnetic free poles and local fields of nucleation and subsequent growth of reversed domains were obtained for a large number of grain boundaries and used to estimate the number and size of Barkhausen events at each angular position from 0 to 360° in ten degree-steps. The good agreement observed between the modeled magnetocrystalline energy and the prediction of this energy made from X-ray texture and Barkhausen noise measurements corroborates the validity of the proposed model.

Investigation of dipolar interaction in FINEMET ribbons through longitudinally driven magneto-impedance effect

The magnetic dipolar interactions among multiple FINEMET ribbons have been studied by longitudinally driven magneto-impedance effect (LDMI) and hysteresis loops in this paper. The effect of dipolar fields on LDMI apparently expands the “bell” magneto-impedance profiles and raises its characteristic frequency. This is essentially correlated with the domain nucleation process under the combined effect of ac driving field and dc external field. A theoretical model was utilized to explicate the LDMI variation with the number of ribbons N. Basically, the nucleation field varied linearly with N. The influence of the frequency of ac current causes the increase of the nucleation field by adding a term He∼f0.38 before 4 MHz, but the dipolar field barely decreases with ac current. At frequency of 10 kHz, the dipolar field is fitted to be about 0.69 Oe, and the geometric factor can be estimated to be 5.60 × 10−5. Additionally the nucleation field reduces slightly due to the compensation of the alternating field, while the LDMI ratio changes obviously. The results indicate that LDMI can be employed as a sensitive tool to reveal the dipolar interaction in FINEMET ribbons and facilitate the design of the materials for magnetic devices.

Nonequilibrium polarization dynamics in antiferroelectrics

A nonequilibrium statistical domain nucleation model of polarization dynamics in less understood antiferroelectric systems is introduced. Predictions of the model have been successfully tested experimentally using an antiferroelectric $\mathrm{P}{\mathrm{b}}_{0.99}\mathrm{N}{\mathrm{b}}_{0.02}{[{(\mathrm{Z}{\mathrm{r}}_{0.57}\mathrm{S}{\mathrm{n}}_{0.43})}_{0.94}\mathrm{T}{\mathrm{i}}_{0.06}]}_{0.98}{\mathrm{O}}_{3}$ polycrystalline ceramic. We determined the activation energy of the domain nucleation process for this particular antiferroelectric sample to be ${W}_{b}=1.07\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ and the critical volume of the polar nucleus ${V}^{*}=98\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}27}{\mathrm{m}}^{3}$, which corresponds to a linear length scale of 2.86 nm.

Field orientation dependence of magnetization reversal in thin films with perpendicular magnetic anisotropy

The magnetization reversal process of hexagonal-close-packed (hcp) (0001) oriented Co and Co90Ru10 thin films with perpendicular magnetic anisotropy (PMA) has been studied as a function of temperature and applied magnetic field angle. Room temperature pure cobalt exhibits two characteristic reversal mechanisms. For angles near in-plane field orientation, the magnetization reversal proceeds via instability of the uniform magnetic state, whereas in the vicinity of the out-of-plane (OP) orientation, magnetization inversion takes place by means of domain nucleation. Temperature dependent measurements enable the modification of the magnetocrystalline anisotropy and reveal a gradual disappearance of the domain nucleation process during magnetization reversal for elevated temperatures. Ultimately, this suppression of the domain nucleation process leads to the exclusive occurrence of uniform state instability reversal for all field orientations at sufficiently high temperature. Comparative magnetic measurements of Co90Ru10 alloy samples allow the identification and confirmation of the high temperature remanent magnetization state of cobalt as an OP stripe domain state despite the reduction of magnetocrystalline anisotropy. Detailed micromagnetic simulations supplement the experimental results and corroborate the physical understanding of the temperature dependent behavior. Moreover, they enable a comprehensive identification of the complex energy balance in magnetic films with PMA, for which three different magnetic phases occur for sufficiently high anisotropy values, whose coexistence point is tricritical in nature.

Domain morphology controlled crystal habits in PbTiO3 nanocrystals

Various crystal habits and associated domain structures in PbTiO3 nanocrystals synthesized by a modified sol–gel method have been studied. Structural and morphological characterizations of synthesized nanoparticles have been done by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found from the -z coordinates of O1 and O2 that the Ti–O6 octahedra were distorted slightly, favorable for the ferroelectric nature. TEM images show butterfly like, plate like, irregular sphere like and oval-shaped habits of the nanocrystals. 90° and 180° domain structures in these crystal habits were explored from their morphologies and appearance in the field of views. The mutual association between the crystal habit and the direction spontaneous polarization Ps due to domain structures was explored. Domain wall energies of 90° and 180° domains were also estimated from the kinetic process of domain nucleation.

Field angle dependent change of the magnetization reversal mode in epitaxial Co (0001) films

The magnetic field dependent reorientation phase transition of epitaxial Co (0001) films with perpendicular magnetic anisotropy is studied as a function of the applied field angle. The experimental data reveal an abrupt qualitative change of the magnetization reversal path at a critical angle between in-plane and out-of-plane field orientation, which is caused by a change in the domain formation process occurring concurrently with the phase transition. By means of our experiments and model calculations, we demonstrate that the observations are due to a transition from instability driven magnetization reversal occurring near in-plane field orientation to domain nucleation processes, which occur near out-of-plane orientation of the magnetic field.

Exotic exchange bias at epitaxial ferroelectric-ferromagnetic interfaces

Multiferroics in spintronics have opened up opportunities for future technological developments, particularly in the field of ferroelectric (FE)-ferromagnetic (FM) oxide interfaces with functionalities. We find strong exchange bias shifts (up to 84 Oe) upon field cooling in metal-oxide (Fe/BaTiO3) films combining FM and FE layers. The saturation magnetic moment of the FM layer is also significantly higher than in bulk (3.0 ± 0.2 μB/atom) and the reversal mechanism occurs via a domain nucleation process. X-ray absorption spectroscopy at the Fe K-edge and Ba L3-edge indicate presence of few monolayers of antiferromagnetic FeO at the interface without the formation of any BaFeO3 layer. Polarized neutron reflectometry corroborates with our magnetization data as we perform depth profiling of the magnetic and structural densities in these bilayers. Our first principles density functional calculations support the formation of antiferromagnetic FeO layers at the interface along with an enhancement of Fe magnetic moments in the inner ferromagnetic layers.

On the Displacement of Adsorbed Polyethylene Glycol by 3-Mercapto-1-Propanesulfonate during Copper Electrodeposition

Displacement of the suppressor polyethylene glycol (PEG) by the accelerant 3-mercapto-1-propanesulfonate (MPS) during copper electrodeposition was studied by a chronoamperometric addition technique. Displacement of PEG occurs through a process of MPS domain nucleation, mass-transfer limited domain expansion and an asymptotic approach to equilibrium between MPS in solution and that on the surface. An isotherm is proposed to account for the equilibrium coverage over a wide range of MPS concentrations, and the nearest neighbor separation between adsorbed MPS molecules during deposition is estimated.

Hydrophobic Mismatch Triggering Texture Defects in Membrane Gel Domains.

The orientational texture of gel-phase lipid bilayers is a phenomenon that can structure membrane domains. Using two-photon polarized fluorescence microscopy and image analysis, we map the lateral variation of the lipid orientation (the texture) in single domains. With this method, we uncover a lipid-induced transition between vortex and uniform textures in binary phospholipid bilayers. By tuning the lipid composition, the hydrophobic mismatch at the domain boundary can be varied systematically as monitored by AFM. Low hydrophobic mismatch correlates with domains having uniform texture, while higher mismatch values correlate with a vortex-type texture. The defect pattern created during early growth persists in larger domains, and a minimal model incorporating the anisotropic line tension and the vortex energy can rationalize this finding. The results suggest that the lipid composition and the domain nucleation process are critical factors that determine the texture pattern of membrane domains.

Nucleation of reversed domain and pinning effect on domain wall motion in nanocomposite magnets

The magnetization behaviors show a strong pinning effect on domain wall motion in optimally melt-spun Pr8Fe87B5 ribbons at room temperature. According to analysis, the coercivity is determined by the nucleation field of reversed domain, and the pinning effect, which results from the weak exchange coupling at interface, makes domain nucleation processes independent and leads to non-uniform magnetization reversals. At a temperature of 60 K, owing to the weak exchange coupling between soft-hard grains, magnetization reversal undergoes processes of spring domain nucleation in soft grains and irreversible domain nucleation in hard grains, and the pinning effect remains strong among hard grains.