Stripe Domain Structure Research Articles

Solitons in the Domain Structure of the Ferromagnet

By the method of dressing on a torus, we obtain and study solutions of the Landau–Lifshitz equation, which describe solitons in the stripe domain structure of the easy-axis ferromagnet. A specific feature of these solitons is that they are directly related to the domain structure: they induce translations and local oscillations of the domains. We find integrals of motion stabilizing the solitons on the background of the structure.

Precessing solitons in the stripe domain structure

New solutions have been found for the Landau-Lifshitz equation for a ferromagnet with easy-axis anisotropy that describe magnetic solitons strongly associated with stripe domain structure. They serve as elementary carriers of macroscopic shifts of the structure and are, under certain conditions, nuclei of the magnetic reversal of a material. It is shown that the inhomogeneous elliptic precession of magnetization in a soliton nucleus leads to perturbations of the adjacent domain walls of a structure. Modulated instability of solitons near the boundaries of their existence is investigated.

Domain Meissner state and spontaneous vortex-antivortex generation in the ferromagnetic superconductor EuFe2(As0.79P0.21)2.

The interplay between superconductivity and magnetism is one of the oldest enigmas in physics. Usually, the strong exchange field of ferromagnet suppresses singlet superconductivity via the paramagnetic effect. In EuFe2(As0.79P0.21)2, a material that becomes not only superconducting at 24.2 K but also ferromagnetic below 19 K, the coexistence of the two antagonistic phenomena becomes possible because of the unusually weak exchange field produced by the Eu subsystem. We demonstrate experimentally and theoretically that when the ferromagnetism adds to superconductivity, the Meissner state becomes spontaneously inhomogeneous, characterized by a nanometer-scale striped domain structure. At yet lower temperature and without any externally applied magnetic field, the system locally generates quantum vortex-antivortex pairs and undergoes a phase transition into a domain vortex-antivortex state characterized by much larger domains and peculiar Turing-like patterns. We develop a quantitative theory of this phenomenon and put forth a new way to realize superconducting superlattices and control the vortex motion in ferromagnetic superconductors by tuning magnetic domains-unprecedented opportunity to consider for advanced superconducting hybrids.

Thickness-dependent resonance frequency of non-uniform procession mode in CoZr stripe-domain magnetic films

The magnetic properties of CoZr magnetic thin films with stripe domains are investigated. The nanocrystalline grain size of 21.2 nm of CoZr thin film was obtained by x-ray diffraction spectra. The rotatable stripe-domain structure of the samples can be clearly observed from the magnetic force microscopy images. From the results of the M–H loop, the typical loops with domain structure of the samples can also be seen. The saturation magnetic fields of the thin films increase as a function of stripe half period in static magnetic properties. In dynamic magnetic properties, we find two precession modes, which include one traditional uniform precession mode with the resonance peak position in the low-frequency band and the other as the non-uniform precession mode with the resonance peak position in the high-frequency band. The ferromagnetic resonance frequencies of the non-uniform procession mode, which are driven by the exchange coupling between adjacent domains, show a decrease in behavior from 5.11to 3.52 GHz in the zero-field dynamic permeability spectra with the stripe domain’s half period increasing, while the ferromagnetic resonance frequencies of the uniform procession mode nearly remain constant. Similar behavior of exchange coupling can be found by analyzing the field-dependent dynamic permeability spectra of CoZr films, which indicates that the main contribution of the thickness-dependent resonance frequency is the exchange coupling between neighboring stripe domains.

Straight motion of half-integer topological defects in thin Fe-N magnetic films with stripe domains

In thin magnetic films with perpendicular magnetic anisotropy, a periodic “up-down” stripe-domain structure can be originated at remanence, on a mesoscopic scale (~100 nm) comparable with film thickness, by the competition between short-range exchange coupling and long-range dipolar interaction. However, translational order is perturbed because magnetic edge dislocations are spontaneously nucleated. Such topological defects play an important role in magnetic films since they promote the in-plane magnetization reversal of stripes and, in superconductor/ferromagnet hybrids, the creation of superconducting vortex clusters. Combining magnetic force microscopy experiments and micromagnetic simulations, we investigated the motion of two classes of magnetic edge dislocations, randomly distributed in an {{rm{N}}}_{2}^{+}-implanted Fe film. They were found to move in opposite directions along straight trajectories parallel to the stripes axis, when driven by a moderate dc magnetic field. Using the approximate Thiele equation, analytical expressions for the forces acting on such magnetic defects and a microscopic explanation for the direction of their motion could be obtained. Straight trajectories are related to the presence of a periodic stripe domain pattern, which imposes the gyrotropic force to vanish even if a nonzero, half-integer topological charge is carried by the defects in some layers across the film thickness.

Study of the magnetization distribution in a grain-oriented magnetic steel using pulsed polarized neutron imaging

The pulsed polarized neutron imaging technique was applied to the observation of the domain structure in a grain oriented magnetic steel sheet with an insulating coating. The spontaneous magnetization of the steel could be quantitatively evaluated from the period of the oscillatory behavior observed in the wavelength dependent polarization. In addition, a striped domain structure in the demagnetized state and the reversal of the magnetization by an external magnetic field were also confirmed by selecting the appropriate combination of the neutron spin direction for the incident and analyzed beams. The results demonstrate that this method can visualize the distribution of the magnetization in a surface-coated magnetic steel.

Tuning the ferromagnetic resonance frequency of soft magnetic film by patterned permalloy micro-stripes with stripe-domain

Periodic micro-stripes arrays with stripe domains structures upon continuous permalloy (Py) film were fabricated by sputtering, photolithography and ion beam etching technology. These samples display in-plane magnetic anisotropy, and stripe domains structure is observed by the magnetic force microscopy (MFM) in the area of the micro-stripes. The periodic micro-stripes show an effective impact on static and dynamic magnetic properties of Py continuous film. In the case of dynamic magnetic properties, the resonance frequency fr of these samples can be tuned by periodic micro-stripes arrays. Compared to continuous film with resonance frequency fr of 0.64 GHz, the fr of composite structures can be tuned by the separation gap of periodic micro-stripes arrays from 0.8 GHz to 2.3 GHz at zero-field. At the same time, the fr could be also tuned by rotating the samples within the plane. This attributes to the competition of shape anisotropy induced by micro-stripes and the dynamic anisotropy originating by stripe domains structure.

Continuum thermodynamics of unusual domain evolution-induced toughening effect in nanocracked strontium titanate

This work is concerned with the analysis of both unusual mechanical and electric behaviors of nanoscale pre-cracked incipient ferroelectric of SrTiO3 at room temperature. A nonlinear thermodynamic model based on the Ginzburg-Landau theory is thus constructed and employed, which takes into account the appropriate mechanical boundary conditions, the electromechanical coupling between the polarization and the mechanical strain, and the self-strains of the ferroelastic and ferroelectric phase transformations. A large toughening effect is explored as a consequence of a softening nonlinear mechanical behavior, which characterizes for nanoscale SrTiO3, despite of the brittleness of bulk SrTiO3 ceramic. Depending upon applied strain, the large toughening and nonlinear mechanical behavior are attributed to unusual domain evolution of strain-induced polarization from the crack tip, in which a local-to-global transition of ferroelectric phase takes place from polarization vortex to hybrid structure of vortex and stripe domains, and finally to stripe domain structure with Néel type domain walls. Here, we also show the great importance of cross-coupling between the ferroelectric polarization and mechanical strain as it intrinsically leads to the local-to-global transition of ferroelectric phase. More interestingly, such cross-coupling additionally scatters the concentrated stress near the crack tip to Néel type domain walls. The present findings shed light on the crucial role of mechanical strain in controlling both the size and topology of polarization structures in nanoscale SrTiO3. Our numerical results also provide an insight into the vital role of strain-induced polarization for the toughness and strength of SrTiO3 material. Based on our study, the applicability of the present results to other incipient ferroelectrics such as CaTiO3, EuTiO3, and KTaO3 with the same mechanism would be interesting and possible.

Thickness-dependent on the static magnetic properties and dynamic anisotropy of FeNi films with stripe domain structures

FeNi stripe domain (SD) films with broad range of film thicknesses were prepared by electrodeposition method. The static magnetic properties and domain structures as well as the fundamental magnetic parameters of perpendicular anisotropy constant Kp, quality factor Q, critical thickness tc, and domain width w for SD films were studied both from experiment and calculation way respectively. The results showed that the Kp, Q, and w of SD films increased when the film thickness increased. In addition, the thickness dependence of the dynamic properties of FeNi SD films was further studied by a vector network analyzer ferromagnetic resonance. The results indicated a decreased dynamic anisotropy when the films thickness or the applied magnetic field increased. This was related to the enhanced SD structures of film when the thickness increased.

Motion and Interaction of Magnetic Dislocations in Alternating Magnetic Field

The behavior of magnetic dislocations (MDs) in an alternating harmonic magnetic field in iron garnets has been experimentally investigated. The results are presented for single-crystal plates in which the drift of domain walls is observed in fields of sound frequencies. It is found that MDs in a stripe domain structure are able to move not only along but also across domain walls. A pairwise interaction between magnetic dislocations when they approach each other to distances on the order of the sizes of the cores of MDs is revealed. The processes of the annihilation, mutual passing of magnetic dislocations through each other and overtaking are found. The features of the dynamic behavior of MDs are explained using a mechanism based on the presence of vertical Bloch lines in a structure of domain walls. MDs are formed at nucleation centers, and their nucleation field is lower than the drift-starting field, which corresponds to previously proposed dislocational mechanism of the drift. The dependencies of quantitative parameters of the drift and MDs on amplitude and frequency of the pumping field are determined. The behavior of MDs should be considered when analyzing the mechanisms for magnetization and temperature-dependent phase transitions in magnetic layers.

Domain structure and magnetization curves of films with perpendicular anisotropy

Based on a two-dimensional micromagnetic simulation, the dependence of the period of a stripe domain structure on the thickness of Co(0001) and Ni(111) films has been obtained, which agrees well with the experimental data. A comparison has been carried out of the calculated and experimental hysteresis loops for a 50-nm Co film and 200-nm Ni film.

V-Shaped Domain Wall Probes for Calibrated Magnetic Force Microscopy

Magnetic force microscopy (MFM) qualitatively resolves stray magnetic fields, but its fundamental flaws include limited quantitative analysis and difficulties in measuring samples with heterogeneous magnetic areas. We propose a custom-made domain wall probe (DWP) with a $V$ -shaped magnetic nanostructure on one face of a non-magnetic probe, which behaves as a low moment probe with high coercivity to reduce magnetic switching in the presence of strong stray fields. The performance of the DWP is compared against commercial standard and low moment probes with different approaches to quantify resolution from striped domain structures of a thin reference film. The three probes are calibrated by acquiring the tip-transfer function (TTF) from a Fourier transform approach. The calculated TTF is used to predict the MFM response from a permalloy nanostructure and compared to experimental results.

Crystalline, magnetic and domain structure of epitaxial ferritegarnet films (review)

The article gives a literary review of the current state of research of ferrite-garnet films. The basic crystalline and magnetic characteristics of thin films of iron-yttrium garnet are considered. We analyzed the causes of the appearance of the labyrinth, stripe and cylindrical domain structure. It is shown that the domain structure of the yttrium iron garnet strongly depends on many parameters of the films, in particular on the thickness, structural perfection of the surface and the sample as a whole. The article reviews the most common methods of synthesis, ion implantation and post-growth treatment of ferrite-garnet films. The study of dependencies between the conditions of obtaining, the chemical composition, the posttreatment conditions, the defective structure and the magnetic properties of ferrite-garnet films have great practical value for obtaining films with predetermined properties.

Magnonic band structure in a Co/Pd stripe domain system investigated by Brillouin light scattering and micromagnetic simulations

By combining Brillouin light scattering and micromagnetic simulations, we studied the spin-wave (SW) dynamics of a Co/Pd thin film multilayer, which features a stripe domain structure at remanence. The periodic up and down domains are separated by corkscrew type domain walls. The existence of these domains causes a scattering of the otherwise bulk and surface SW modes, which form mode families, similar to a one-dimensional magnonic crystal. The dispersion relation and mode profiles of SWs are measured for the transferred wave vector parallel and perpendicular to the domain axis.

Generation of high-density biskyrmions by electric current

Much interest has been focused on the manipulation of magnetic skyrmions, including the generation, annihilation, and motion behaviors, for potential applications in spintronics. Here, we experimentally demonstrate that a high-density Bloch-type biskyrmion lattice in MnNiGa can be generated by applying electric current. It is revealed that the density of biskyrmions can be remarkably increased by increasing the electric current, in contrast to the scattered biskyrmions induced by a magnetic field alone. Furthermore, the transition from the ferromagnetic state to the stripe domain structure can be terminated by the electric current, leading to the biskyrmions dominated residual domain pattern. These biskyrmions in such residual domain structure are extremely stable at zero magnetic and electric fields and can further evolve into the high-density biskyrmion lattice over a temperature range from 100 to 330 K. Our experimental findings open up a new pathway for the generation of skyrmion lattice by electric current manipulation.

Ferromagnetic resonance in Mn5Ge3 epitaxial films with weak stripe domain structure

Extensive X-band and Q-band FMR experiments have been performed in the Mn5Ge3 epitaxial films with thicknesses varying between 4.5 and 68 nm. FMR signals were recorded in the temperature range between 15 and 295 K, at different orientations of magnetic field with respect to the film plane. In addition to the acoustic FMR mode with well defined resonance field, originating from inside the magnetic domains, a broad absorption line has been observed at low fields and attributed to the unresolved spectrum of FMR modes having the origin in flux closure caps. The FMR results have been discussed in the context of the domain structure computed with the use of OOMMF micromagnetic calculations and giving good agreement with the experimental hysteresis curves. From the Q-band experiments, where the FMR signal is observed in the magnetically saturated sample, the uniaxial anisotropy constant in films with different thicknesses has been determined as a function of temperature. This FMR study provides the evidence that the strong uniaxial anisotropy observed in epitaxial thin films of Mn5Ge3 leads to the formation of a stripe domain structure above 25 nm, in agreement with the published reports on magnetization studies in these films. It also eliminates a possible confusion that may arise from previously published FMR studies on films grown with the same method, which led their authors to conclude that the shape anisotropy can force the magnetization to the in-plane orientation in this thickness range and even above it.

圧電体基板上に作製したNiCu合金微小磁性細線の磁気抵抗効果

The magnetoresistance measurements of NiCu micro-wires with various widths fabricated on a LiNbO3 substrate were performed. An external magnetic field dependence of the magnetoresistances indicated that stripe domain structure can be also formed in the NiCu micro-wires. The competition of shape anisotropy and magnetic anisotropy induced by magnetoelastic effect enables us to control domain structure and magnetization reversal characteristics.

Magnetic Domain Structure and Magnetostriction of Fe-Ga Single Crystal Grown by the Czochralski Method

The magnetic domain structure on the (0 0 1) plane of an Fe 16.1 Ga 83.9 single crystal grown by the Czochralski method was observed by magneto-optic Kerr effect microscopy. In zero magnetic field, four different domain phases appeared, with magnetization in four kinds of '1 0 0 magnetic easy directions on the (0 0 1) plane. That is, the magnetic domain structure in zero field was composed of straight 90° domain walls and stair-like 180° domain walls. When a magnetic field was applied in the [0 1 0] direction, primarily 180° domain walls moved, whereas 90° domain walls did not. A striped domain structure composed of 90° domain walls was formed at a field of about 560 Oe, 180° domain walls having almost disappeared. A single domain structure was obtained by applying a field of about 1980 Oe. Magnetostriction in the [0 1 0] direction on the (0 0 1) plane was only about 10 ppm in a field of about 560 Oe and reached a saturation value of about 153 ppm at a field of about 1980 Oe. This magnetostrictive behavior contributes to the evolution of the magnetic domain structure.

Local ferroelectricity at the domain walls and stripe domain heads in iron garnet films

ABSTRACTThe concept of local ferroelectricity discussed in this paper belongs to the emerging field of ultrathin multiferroics. The idea of the ferroelectric polarization associated with the domain walls in magnets proposed by V.G. Bar'yakhtar et al. more than thirty years ago has recently got experimental evidence including electric field driven magnetic domain wall motion and electric field induced Stark shift in the single molecule microscopy. The special attention is paid here to the magnetoelectric properties of dislocation in stripe domain structure (i.e. the stripe domain heads) that differ considerably from the ones of straight domain wall segments. It is shown that the electric field induced displacement of the domain wall can be increased by an order of value with external constant magnetic field.

Influence of the rotation frequency of the magnetic field on the dynamics of the domain structure of thin Fe–3% Si crystals

Some specific features of the reconstruction of the domain structure of thin (0.10 mm) Fe–3% Si single crystals have been investigated depending on the frequency of the magnetization reversal in rotating magnetic fields. The studies have been carried out in the range of frequencies of 60–300 Hz and induction amplitudes of 0.5–1.6 T. It has been established that the magnetization reversal of the samples of this thickness occurs via the displacements of 180° domain walls of the stripe domain structure without the participation of the C-domain walls. A qualitative explanation to the revealed features of the behavior of the domain structure has been given, and their possible contribution to the magnetic losses of the investigated samples has been evaluated.