Magnetic Domain Configuration Research Articles

On the correlation between magnetic domain and crystallographic grain orientation in grain oriented electrical steels

The deviation angle of the easy magnetisation 〈0 0 1〉-axes from the rolling direction (RD) strongly affects the magnetic domain configuration within individual grains and hence the overall magnetic properties in grain oriented electrical steels (GOES). In the current study, both angles of deviations; α: the angle between 〈0 0 1〉 and in-plane rolling direction, and β: the angle between 〈0 0 1〉 and out-plane rolling direction, where calculated using electron backscatter diffraction (EBSD) raw data to investigate the exact correlation between the crystal orientation and magnetic domain structure. Further, EBSD combined with forescatter detector (FSD) is used to reveal the magnetic domain configuration within individual oriented grains. The microstructure and microtexture of various GOESs with different chemical compositions and magnetic properties were characterised. The magnetic domain patterns were directly imaged and correlated to the crystal orientation and α and β deviation angles. It is demonstrated that the crystal orientation has a great impact on the magnetic domain patterns, width, and configurations. It was also shown that the grain boundary characteristics have a significant influence on the magnetic domain transfer between neighbouring grains. It was evident that low angle grain boundaries allowed domain transfer without a significant change in the domain pattern, whereas high angle grain boundaries perturbed the magnetic domain pattern, width, and configuration. Furthermore, it was demonstrated that the size of the deviated orientation grains from ideal (1 1 0) 〈0 0 1〉 GOSS orientation is a critical microtexture parameter for the optimisation of magnetic property. Finally, it is concluded that the magnetic domain patterns and α and β angle of deviations are strongly correlated to the magnetic losses in GOES.

Antiparallel exchange biased multilayers for low magnetic noise magnetic field sensors

High sensitivity magnetoelectric (ME) thin film composite sensors, which enable the detection of picotesla magnetic fields, are improved in terms of magnetic noise performance by the elimination of magnetic domain (MD) activity. Using an antiparallel (AP) exchange biasing scheme, suppression of magnetic noise is obtained. Postsetting of AP biased ferromagnetic/antiferromagnetic multilayers is accomplished by magnetic field free annealing with in-situ MD control. Overcoming the shape and demagnetization effects, stable single MD configurations in the magnetic sensing layers of magnetic multilayers are formed. Magnetic noise contributions are undetectable. The achieved single domain field stability opens the path to ultralow noise ME sensor applications. The demonstrated AP biasing scheme is applicable to other magnetic layer-based field sensing devices.

Influence of magnetic domain wall orientation on Barkhausen noise and magneto-mechanical behavior in electrical steel

We investigate the influence of magnetic domain configurations on the magnetic Barkhausen noise (MBN) and magneto-mechanical behavior of electrical steel. Micro-macro magnetic properties from individual crystallographic grains with different domain wall (DW) orientations under different tensile stresses are measured. We show a strong dependency of the MBN activity and magneto-mechanical behavior on the DW orientation. Time evolution and statics of magnetic domain states are elaborated for the analysis of the magnetization processes, revealing an interaction between the stress-induced demagnetizing effect, the magneto-elastic behavior and the DW dynamics. The variation of supplementary domains under tensile stress is directly connected to the demagnetizing effect, further affecting the MBN activity. In addition, the influence of magnetic domain configurations in the neighboring grains on the DW dynamics and MBN jumps is studied. From this, the dipolar-dipolar and intergranular magnetic coupling interactions are derived. The results provide substantial microscopic insight for MBN and magneto-mechanical behavior analysis.

Magnetic domains characterization of crystalline Fe3O4 under DC and AC magnetic field.

Fe3O4 nanoparticles with crystallite sizes around 10 nm were synthesized by an emulsion method. X-ray diffractometer (XRD) shows that nanocrystalline Fe3O4 possesses face center cubic structure. The magnetic characteristics are investigated by magnetic force microscopy (MFM). Magnetic field directions were applied parallel and perpendicular to the Fe3O4 sample surface for magnetic measurements. Under the perpendicular magnetic field, the phase images of most magnetic nanoparticles exhibit bright or dark MFM contrast. In comparison, the parallel field phase images display a bright-dark dipole MFM contrast, with in-plane magnetic domain configurations. Furthermore, the investigation of strip domains inside Fe3O4 particles under altering magnetic fields indicates the existence of magnetic anisotropy energies, dipole energies as well as inter-grain coupling energies inside the clusters. This approach for probing magnetic responses on nanoscale magnetic domains can be further extended to the analysis of local physical features.

Stimulated CO Dissociation and Surface Graphitization by Microfocused X-ray and Electron Beams

The irradiation with photons or electrons can dramatically influence the chemical stability of a molecule, either free or adsorbed on a surface, inducing its fragmentation or desorption. We revisit here the exostimulated dissociation of CO, a prototypical case, choosing hcp thin cobalt films as model support. Intense, microfocused soft X-rays or electron beams are used to locally stimulate CO dissociation. Fast-XPS gives direct access to the adsorbates’ chemical state and coverage during irradiation, enabling the kinetics of the process to be monitored in real time. The energy-dependent cross sections for photon and electron stimulated molecular dissociation and desorption are estimated for a fixed initial CO coverage of 1/3 ML. In the soft X-ray regime, the desorption channel always prevails over dissociation and is significantly enhanced above the O K edge. The relative dissociation probability increases steadily with increasing photon energy, reaching 30% at 780 eV. Furthermore, we show that low energy electrons in the range 50 to 200 eV dissociate CO more efficiently than X-rays. The prolonged irradiation of the Co surface in CO ambient is found to produce a continuous increase of the carbon coverage, initially promoting the formation of carbides and subsequently accumulating sp2 carbon on the surface. Far from being a detrimental effect, the CO stimulated dissociation can be exploited to lithographically graft carbon-rich microscopic patterns on Co, with resolution well into the nanometer scale. A brief thermal treatment following irradiation results in the formation of a graphitic carbon overlayer, which effectively protects Co from oxidation upon exposure to ambient conditions, preserving its out-of-plane magnetic anisotropy and domain configuration.

Electric Control of the Magnetic Domains in Artificial Magnetoelectric Composite Heterostructure

Magnetic force microscopy (MFM) has been used to probe the influence of an in situ applied in-plane elastic strains and/or magnetic field on the static magnetic configuration of a 530 nm magnetostrictive FeCuNbSiB thin film. The film shows a typical magnetic stripe domain configuration with 180 nm magnetic domain width presenting its magnetic moments oriented perpendicularly to the film plane. The in-plane strain was induced via the application of a voltage in a piezoelectric (PE) actuator on which the film/substrate system was glued. The FeCuNbSiB film was deposited onto a compliant polyimide substrate (Kapton) in order to avoid clamping effects that can lead to low transmission of strains from the actuator to the film/substrate system. The instrumental setup was modified with a custom-built electromagnet for performing in situ MFM experiments under the application of an in-plane magnetic field. We could compare the strain-mediated effect upon the magnetic domain configuration with the effect of an applied magnetic field. This paper clearly shows a better-defined electric field/strain control of the local domain magnetization (size and orientation). The efficient coupling between the magnetostrictive properties of the FeCuNbSiB film and the PE ones of the actuators allows a complete switching of the out-of-plane domain magnetization toward an in-plane homogeneous magnetic one. This magnetoelectric heterostructure can thus open the way for new devices allowing the electric control of the magnetic information at the nanoscale level.

Phase Coexistence and Kinetic Arrest in the Magnetostructural Transition of the Ordered Alloy FeRh

In materials where two or more ordering degrees of freedom are closely matched in their free energies, coupling between them, or multiferroic behavior can occur. These phenomena can produce a very rich phase behavior, as well as emergent phases that offer useful properties and opportunities to reveal novel phenomena in phase transitions. The ordered alloy FeRh undergoes an antiferromagnetic to ferromagnetic phase transition at ~375 K, which illustrates the interplay between structural and magnetic order mediated by a delicate energy balance between two configurations. We have examined this transition using a combination of high-resolution x-ray structural and magnetic imaging and comprehensive x-ray magnetic circular dichroism spectroscopy. We find that the transition proceeds via a defect-driven domain nucleation and growth mechanism, with significant return point memory in both the structural and magnetic domain configurations. The domains show evidence of inhibited growth after nucleation, resulting in a quasi-2nd order temperature behavior.

Effect of deposition temperature on morphological, magnetic and elastic properties of ultrathin Co 49 Pt 51 films

Abstract Morphological, magnetic and elastic properties of 5 nm-thick Co 49 Pt 51 films, sputtered on glass substrates, with 20 nm-thick Ta (seed) and Pt (buffer) layers were studied as function of the deposition temperature T d ranging between room temperature and 350° C. Atomic and magnetic force microscopy, vibrating sample magnetometer and Brillouin light scattering techniques were used to investigate the root mean square (RMS) roughness, the magnetic domain configuration, the coercive field (H c ), the perpendicular magnetic anisotropy (PMA), and the dynamic magnetic and elastic properties of the films with T d . The results show that surface uniformity was enhanced since the RMS roughness decreases with T d while magnetic domains typical of films with high PMA are observed. H c and PMA are found to sensibly increase with T d . The dynamic magnetization behavior is characterized by magnetic modes related with the co-existence of hard and soft magnetic areas within the samples. The elastic properties of the stack were first analyzed by means of a model describing the main variation of the elastic wave frequencies within the frame of weighted average thickness, density, Young’s modulus and Poisson coefficient of all the layers constituting the stacks. However, while H c and PMA keep increasing with T d , a more precise experimental analysis of the mechanical behavior shows that the group velocity starts increasing and finally decreases with T d , suggesting that knowledge of the influence of T d on the mechanical properties of each individual layer composing the stack is required to obtain a more accurate analysis.

Multisegmented Nanowires: a Step towards the Control of the Domain Wall Configuration

Cylindrical nanowires synthesized by controlled electrodeposition constitute excellent strategic candidates to engineer magnetic domain configurations. In this work, multisegmented CoNi/Ni nanowires are synthesized for tailoring a periodic magnetic structure determined by the balance between magnetocrystalline and magnetostatic energies. High-resolution Transmission Electron Microscopy confirms the segmented growth and the sharp transition between layers. Although both CoNi and Ni segments have similar fcc cubic crystal symmetry, their magnetic configuration is quite different as experimentally revealed by Magnetic Force Microscopy (MFM) imaging. While the Ni segments are single domain with axial magnetization direction, the CoNi segments present two main configurations: a single vortex state or a complex multivortex magnetic configuration, which is further interpreted with the help of micromagnetic simulations. This original outcome is ascribed to the tight competition between anisotropies. The almost monocrystalline fcc structure of the CoNi segments, as revealed by the electron diffraction patterns, which is atypical for its composition, contributes to balance the magnetocrystalline and shape anisotropies. The results of MFM measurements performed under in-plane magnetic field demonstrate that it is possible to switch from the multivortex configuration to a single vortex configuration with low magnetic fields.

Direct imaging of delayed magneto-dynamic modes induced by surface acoustic waves

The magnetoelastic effect—the change of magnetic properties caused by the elastic deformation of a magnetic material—has been proposed as an alternative approach to magnetic fields for the low-power control of magnetization states of nanoelements since it avoids charge currents, which entail ohmic losses. Here, we have studied the effect of dynamic strain accompanying a surface acoustic wave on magnetic nanostructures in thermal equilibrium. We have developed an experimental technique based on stroboscopic X-ray microscopy that provides a pathway to the quantitative study of strain waves and magnetization at the nanoscale. We have simultaneously imaged the evolution of both strain and magnetization dynamics of nanostructures at the picosecond time scale and found that magnetization modes have a delayed response to the strain modes, adjustable by the magnetic domain configuration. Our results provide fundamental insight into magnetoelastic coupling in nanostructures and have implications for the design of strain-controlled magnetostrictive nano-devices.

Magnetic domain wall engineering in a nanoscale permalloy junction

Nanoscale magnetic junctions provide a useful approach to act as building blocks for magnetoresistive random access memories (MRAM), where one of the key issues is to control the magnetic domain configuration. Here, we study the domain structure and the magnetic switching in the Permalloy (Fe20Ni80) nanoscale magnetic junctions with different thicknesses by using micromagnetic simulations. It is found that both the 90-° and 45-° domain walls can be formed between the junctions and the wire arms depending on the thickness of the device. The magnetic switching fields show distinct thickness dependencies with a broad peak varying from 7 nm to 22 nm depending on the junction sizes, and the large magnetic switching fields favor the stability of the MRAM operation.

Manipulation of anisotropic magnetoresistance and domain configuration in Co/PMN-PT (011) multiferroic heterostructures by electric field

The electric field manipulation of magnetic anisotropy and domain configuration has been investigated in the artificial multiferroic Co/PMN-PT (011) heterostructure at room temperature. A uniaxial magnetic anisotropy is induced with the application of an electric field, which leads to an electrically switched anisotropic magnetoresistance with tunability as large as ∼29%. Furthermore, the magnetic domain structures of Co films are investigated by magnetic force microscopy under an in situ electric field, which exhibits direct evidence for electric field control of magnetism at the mesoscale. The converse magnetoelectric effect demonstrated in this multiferroic heterostructure has potential to be utilized in magnetoelectric devices with low power consumption.

In situ observation of magnetic vortex manipulation by external fields in amorphous CeFeB ribbon

In this study, we show the real-space observation of the magnetic domain configuration in amorphous Ce14Fe80B6 ribbon using Lorentz transmission electron microscopy. Cross-tie domain walls composed of magnetic vortices (Vs) and antivortices (AVs) are observed. The evolution of Vs/AVs manipulated by temperature, in-plane magnetic field, and electrical current is clearly demonstrated. Magnetic V nucleation and annihilation in pair are observed because of the stimulus of external fields.

Syntheses of iron oxide nanoplates by hydrothermal treatment of iron-oleate precursor and their magnetization reversal

Magnetic iron oxide (Fe3−xO4) nanoplates with a high aspect ratio (lateral size/thickness ratio of>50) were synthesized via a facile hydrothermal treatment of an iron-oleate precursor. The magnetic domain configuration of the Fe3−xO4 nanoplates was observed by magnetic force microscopy (MFM). Single domain magnetic polarity was observed in the remnant state of isolated Fe3−xO4 nanoplates, with a lateral size of ca. 300nm and thickness of 7.6nm. The magnetization orientation of isolated Fe3−xO4 nanoplates was mainly determined by the magnetic shape anisotropy originating from their high aspect ratio. Magnetization reversal occurred via coherent rotation upon switching the external magnetic field, rather than by domain wall nucleation. Micro-magnetic simulations based on the Landau-Lifshitz Gilbert equation supported the conclusions drawn from the experimental results.

Defect dynamics and strain coupling to magnetization in the cubic helimagnet Cu2OSeO3

Small but significant static and dynamic strain coupling effects have been detected in $\mathrm{C}{\mathrm{u}}_{2}\mathrm{OSe}{\mathrm{O}}_{3}$ through elastic and anelastic anomalies associated with magnetic phase transitions observed as a function of temperature (1.5--150 K) and magnetic field (0--300 mT). The magnetic transition near 60 K is accompanied by a small increase in single-crystal elastic constants which can be understood in terms of biquadratic coupling between shear strain and the magnetic order parameter, even though the shear strain itself is almost negligibly small. The conical-collinear transition is associated with distinct minima in the elastic properties, while weaker anomalies at lower fields may be related to changes in the configuration of magnetic domains. A distinctive acoustic loss peak at $\ensuremath{\sim}42\phantom{\rule{4.pt}{0ex}}\text{K}$, independent of magnetic field, is attributed to freezing of a defect which is coupled with shear strain, has an associated activation energy of $\ensuremath{\sim}5\phantom{\rule{4.pt}{0ex}}\text{kJ}\phantom{\rule{4.pt}{0ex}}\text{mo}{\mathrm{l}}^{\ensuremath{-}1}$, and may play a role in pinning the magnetic microstructures. Anomalies below $\ensuremath{\sim}10\phantom{\rule{4.pt}{0ex}}\text{K}$ indicate the presence of some additional relaxation process which could signify a change in magnetic structure.

Magnetic coupling of stripe domains in FePt/Ni80Fe20 bilayers

Equiatomic FePt in the A1 soft magnetic phase and Ni80Fe20 (permalloy) thin films form a stripe-like magnetic domain structure above a critical thickness. This critical thickness is considerably different in the two alloys and allows us to study the influence of the magnetic coupling in the domain configuration in bilayers. Using dc magnetron sputtering techniques, we fabricated two different sets of FePt/Ni80Fe20 bilayers, keeping one thickness fixed and varying the other, and investigated the dc magnetic properties and the magnetic domain configuration of the structure. In all cases, magnetization reversal occurred at a single coercive field, indicating a relatively strong magnetic exchange coupling between both layers. The observed stripe period was also consistent with a model of spring magnet-like behavior. However, for certain values of FePt and permalloy thickness a complex nonparallel double stripe structure was found, which may be attributed to the influence of the dipolar stray field of the thicker layer on the stripe structure of the thinner film.

Effect of lithographically-induced strain relaxation on the magnetic domain configuration in microfabricated epitaxially grown Fe81Ga19

We investigate the role of lithographically-induced strain relaxation in a micron-scaled device fabricated from epitaxial thin films of the magnetostrictive alloy Fe81Ga19. The strain relaxation due to lithographic patterning induces a magnetic anisotropy that competes with the magnetocrystalline and shape induced anisotropies to play a crucial role in stabilising a flux-closing domain pattern. We use magnetic imaging, micromagnetic calculations and linear elastic modelling to investigate a region close to the edges of an etched structure. This highly-strained edge region has a significant influence on the magnetic domain configuration due to an induced magnetic anisotropy resulting from the inverse magnetostriction effect. We investigate the competition between the strain-induced and shape-induced anisotropy energies, and the resultant stable domain configurations, as the width of the bar is reduced to the nanoscale range. Understanding this behaviour will be important when designing hybrid magneto-electric spintronic devices based on highly magnetostrictive materials.

High-resolution hard x-ray magnetic imaging with dichroic ptychography

Imaging the magnetic structure of a material is essential to understanding the influence of the physical and chemical microstructure on its magnetic properties. Magnetic imaging techniques, however, have up to now been unable to probe 3D micrometer-sized systems with nanoscale resolution. Here we present the imaging of the magnetic domain configuration of a micrometre-thick FeGd multilayer with hard X-ray dichroic ptychography at energies spanning both the Gd L3 edge and the Fe K edge, providing a high spatial resolution spectroscopic analysis of the complex X-ray magnetic circular dichroism. With a spatial resolution reaching 45 nm, this advance in hard X-ray magnetic imaging is the first step towards the investigation of buried magnetic structures and extended three-dimensional magnetic systems at the nanoscale.

Effect of synthesis on structure, oxygen voids, valence bands, forbidden band gap and magnetic domain configuration of La2CoMnO6

La2CoMnO6 were prepared by the solid state reaction (SSR) and the sol-gel method (SGM). Compared to SSR, the SGM sample has a smaller lattice. The XPS spectra of O 1s core level of SGM show an extra peak at 533.16 eV, owing to the oxygen deficient region. The valence band of SGM moves to the low energy side by 0.36 eV, compared to that of SSR due to the holes generated by oxygen voids. The forbidden band gap energies are 1.78 eV and 1.93 eV for the SGM and the SSR samples, respectively. At low temperature, both the samples have multiple magnetic phases. Both of them have one ferromagnetic (FM) transition at 153 K and one antiferromagnetic (AFM) transition at 123 K in common, and a spin glass state below 75 K is confirmed. Furthermore, SSR has one extra FM transition at 223 K, while SGM does not have. A magnetic configuration as … spin glass↓ - ↓AFM↓- ↑FM↑- ↓AFM↓- spin glass↓ … is proposed to interpret the magnetic properties. The existence of the AFM clusters and the coupling between the AFM cluster and the FM or the spin glass domains are confirmed by the low magnetization at 70 kOe, the high coercive field of over 10 kOe, and the existence of the magnetic exchange bias.

Microstructural evolution and correlated magnetic domain configuration of nanoparticles embedded in a single crystal of Cu75–Ni20–Fe5 alloy

We have investigated the microstructural evolution and magnetic domain configurations in nano-scale Fe–Ni rich precipitates formed in a single-crystal specimen of Cu–20at%Ni–5at%Fe alloy on isothermal annealing at 873 K and 973 K, using a combination of transmission electron microscopy (TEM), electron backscattering diffraction, field-emission scanning electron microscopy (FE-SEM), and laser-based photoemission electron microscopy (laser-PEEM). The TEM and FE-SEM observations showed that small, spherical solute-rich particles formed randomly in the initial stage of the precipitation, but on isothermal annealing, cubic, rectangular, plate-shaped and rod-shaped precipitates appeared and aligned along the <1 0 0 > directions in the copper-rich matrix. Laser-PEEM was applied to single-crystal specimens of the alloy and allowed direct observations of magnetic domain configurations in individual ferromagnetic particles at the nanometer scale. This revealed that cubic particles of size approximately 50–60 nm consist of single magnetic domains, but particles of size 100 nm have a closed spin structure (e.g. vortex or multiple domains).