Magnetic Domain Patterns Research Articles

Stripe magnetic domains in CeY2Fe5O12 (Ce:YIG) epitaxial films

Thin epitaxial films of CeY2Fe5O12 are deposited on (111) Gd3Ga5O12 substrates using pulsed laser ablation. The films exhibit low coercivity (3 mT), high saturation magnetization (102 mT), and excellent epitaxy. High resolution magnetic force microscopy (MFM) images of the film reveal a prominent stripe magnetic domain pattern due to a non-coplanar magnetization vector M→. Intensity analysis of the MFM images allows extraction of the orientation angle θc of M→ with respect to the plane of the film. We have recorded the changes in the width of the stripes and their disappearance as the strength of an in-plane magnetic field is increased. A simple model based on sinusoidal variation of M→ correctly predicts the change in the width of the stripe domains.

Magnetostriction in grain‐oriented electrical steels under AC magnetisation at angles to the rolling direction

Magnetostriction is an important source of vibration and acoustic noise in electromagnetic cores. This study reports magnetostriction components along the rolling, transverse and magnetisation directions (MDs) of grain-oriented (GO) electrical steels, used for transformer and large rotating machine cores, under magnetisation at angles to the rolling direction (RD). Magnetostriction components in the sheet plane were simultaneously measured using a two-dimensional magnetisation system. Results from the measurements agreed with the magnetostriction calculated from a simplified model of magnetic domain patterns in a 3% SiFe single crystal. It is shown that the magnetostrictive strain along the RD is always the highest component in the sheet plane irrespective of MD. This is expected to cause both additional vibration at the corners of transformer cores where flux deviates from the RD and high radial vibration in the back-iron regions of rotating machine stator cores assembled from segmented GO steel laminations.

Magnetostrictive iron gallium thin films grown onto antiferromagnetic manganese nitride: Structure and magnetism

We report structural and magnetic properties of magnetostrictive Fe100−xGax (x ≈ 15) alloys when deposited onto antiferromagnetic manganese nitride and non-magnetic magnesium oxide substrates. From X-ray diffraction measurements, we find that the FeGa films are single crystalline. Scanning tunneling microscopy imaging reveals that the surface morphologies are dictated by the growth temperature, composition, and substrate. The magnetic properties can be tailored by the substrate, as found by magnetic force microscopy imaging and vibrating sample magnetometry measurements. In addition to pronounced tetragonal deformations, depositing FeGa onto manganese nitride leads to the formation of stripe-like magnetic domain patterns and to the appearance of perpendicular magnetic anisotropy.

Magnetically Patterned Rolled-Up Exchange Bias Tubes: A Paternoster for Superparamagnetic Beads

We realized a deterministic transport system for superparamagnetic microbeads through micrometer-sized tubes acting as channels. Beads are moved stepwise in a paternoster-like manner through the tube and back on top of it by weak magnetic field pulses without changing the field pulse polarity and taking advantage of the magnetic stray field emerging from the tubular structures. The microtubes are engineered by rolling up exchange bias layer systems, magnetically patterned into parallel stripe magnetic domains. In this way, the tubes possess distinct azimuthally aligned magnetic domain patterns. This transport mechanism features high step velocities and remote control of not only the direction and trajectory but also the velocity of the transport without the need of fuel or catalytic material. Therefore, this approach has the potential to impact several fields of 3D applications in biotechnology, including particle transport related phenomena in lab-on-a-chip and lab-in-a-tube devices.

Imprinting superconducting vortex footsteps in a magnetic layer.

Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories.

Robustness of magnetic and electric domains against charge carrier doping in multiferroic hexagonal ErMnO3

We investigate the effect of chemical doping on the electric and magnetic domain pattern in multiferroic hexagonal ErMnO3. Hole- and electron doping are achieved through the growth of Er1−xCaxMnO3 and Er1−xZrxMnO3 single crystals, which allows for a controlled introduction of divalent and tetravalent ions, respectively. Using conductance measurements, piezoresponse force microscopy and nonlinear optics we study doping-related variations in the electronic transport and image the corrsponding ferroelectric and antiferromagnetic domains. We find that moderate doping levels allow for adjusting the electronic conduction properties of ErMnO3 without destroying its characteristic domain patterns. Our findings demonstrate the feasibility of chemical doping for non-perturbative property-engineering of intrinsic domain states in this important class of multiferroics.

Magnetic stripe domains of [Pt/Co/Cu]10 multilayer near spin reorientation transition

The dependence of magnetic anisotropy, magnetic domain patterns and magnetization reversal processes in [Pt/Co(tCo)/Cu]10 film stack epitaxied on Cu (111) substrate have been studied as a function of the Co layer thickness tCo, by magneto-optic polar Kerr magnetometry and microscopy. We find the film undergoes spin reorientation transition from out-of-plane to in-plane as tCo increases. The SRT thickness is verified by Rotating-field Magneto-Optic Kerr effect method. The film exhibits the stripe domain structures at remanence with the width decreasing while tCo approaches SRT. As demonstrated by the first order reversal curve measurement, the magnetization reversal process encompasses irreversible domain nucleation, domain annihilation at large field and reversible domain switching near remanence.

Changes in magnetic domain structure during twin boundary motion in single crystal Ni-Mn-Ga exhibiting magnetic shape memory effect

The complexity of Ni-Mn-Ga single crystal originates from the interplay between ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure in the vicinity of single twin boundary was studied using magneto-optical indicator film and magnetic force microscopy technique. The single twin boundary of Type I was formed mechanically and an initial magnetization state in both variants were restored by local application of magnetic field (≈40 kA/m). The differently oriented variants exhibited either stripe or labyrinth magnetic domain pattern in agreement with the uniaxial magnetocrystalline anisotropy of the martensite. The twin boundary was then moved by compressive or tensile stress. The passage of the boundary resulted in the formation of granular or rake domains, respectively. Additionally, the specific magnetic domains pattern projected by twin boundary gradually vanished during twin boundary motion.

Soft x-ray ptychography studies of nanoscale magnetic and structural correlations in thin SmCo5 films

High spatial resolution magnetic x-ray spectromicroscopy at x-ray photon energies near the cobalt L3 resonance was applied to probe an amorphous 50 nm thin SmCo5 film prepared by off-axis pulsed laser deposition onto an x-ray transparent 200 nm thin Si3N4 membrane. Alternating gradient magnetometry shows a strong in-plane anisotropy and an only weak perpendicular magnetic anisotropy, which is confirmed by magnetic transmission soft x-ray microscopy images showing over a field of view of 10 μm a primarily stripe-like domain pattern but with local labyrinth-like domains. Soft x-ray ptychography in amplitude and phase contrast was used to identify and characterize local magnetic and structural features over a field of view of 1 μm with a spatial resolution of about 10 nm. There, the magnetic labyrinth domain patterns are accompanied by nanoscale structural inclusions that are primarily located in close proximity to the magnetic domain walls. Our analysis suggests that these inclusions are nanocrystalline Sm2Co17 phases with nominally in-plane magnetic anisotropy.

Magnetic microstructure in a stress-annealed Fe73.5Si15.5B7Nb3Cu1 soft magnetic alloy observed using off-axis electron holography and Lorentz microscopy

Fe-Si-B-Nb-Cu alloys are attractive for high frequency applications due to their low coercivity and high saturation magnetization. Here, we study the effect of stress annealing on magnetic microstructure in Fe73.5Si15.5B7Nb3Cu1 using off-axis electron holography and the Fresnel mode of Lorentz transmission electron microscopy. A stress of 50 MPa was applied to selected samples during rapid annealing for 4 s, resulting in uniaxial anisotropy perpendicular to the stress direction. The examination of focused ion beam milled lamellae prepared from each sample revealed a random magnetic domain pattern in the sample that had been rapidly annealed in the absence of stress, whereas a highly regular domain pattern was observed in the stress-annealed sample. We also measured a decrease in domain wall width from ∼ 94 nm in the sample annealed without stress to ∼ 80 nm in the stress-annealed sample.

Analysis of Magnetic Relaxation With Pre-Existing Nucleation Sites Based on the Fatuzzo–Labrune Model

Time-resolved magnetic domain patterns of (Co/Pt) and (CoFeB/Pd) multilayers with perpendicular magnetic anisotropy are observed by means of magneto-optical microscopy, from which magnetic relaxation curves are determined for. Interestingly, it has been observed that the relaxation processes not only from the saturated state, but also with pre-existing domains, are well explained based on the Fatuzzo-Labrune model [1, 2]. Full details of the relaxation behavior and subsequent microscopic domain patterns evolving from the pre-existing nucleation sites originated from the sub-structured magnetic domains are discussed.

Effect of Ta Underlayer on Thickness-Dependent Magnetic Properties of Ni–Fe Films

We report the effect of Ta underlayer on the structural and the magnetic properties of Permalloy (Ni81Fe19) thin films over a wide range of film thicknesses ( t Ni–Fe = 10–200 nm). For this purpose, Ta (5 nm)/Ni–Fe ( t Ni–Fe nm)/Ta (2 nm) films were grown on thermally oxidized Si substrates under the presence and the absence of biasing magnetic field (1000 Oe). The Ni–Fe films grown under the presence and the absence of biasing magnetic fields are referred to Ta/Ni–Fe(M) and Ta/Ni–Fe(NM), respectively. X-ray diffraction studies revealed that the Ta underlayer plays an important role in the formation of fcc-(111) Ni–Fe texture in both the Ta/Ni–Fe(M) and Ta/Ni–Fe(NM) films. In addition, the values of average crystallite size depend on the film thickness, biasing field, and Ta underlayer. Thickness-dependent magnetic hysteresis ( M–H ) loops demonstrate a strong in-plane uniaxial anisotropy in both the Ta/Ni–Fe(NM) and Ta/Ni–Fe(M) films. The uniaxial anisotropy constant ( Ku ) depends not only on the film thickness, but also strongly on the biasing magnetic field. Coercivity decreases with increasing film thickness for both the Ta/Ni–Fe(NM) and Ta/Ni–Fe(M) films, and approaches to a minimum of $\sim$ 0.4 Oe even at t Ni–Fe = 200 nm. Furthermore, the observed magnetic domain patterns of Ni–Fe films show their dependence on the Ta underlayer, biasing field, and Ni–Fe thickness. The effects of the Ta underlayer, the Ni–Fe film thickness, and the biasing-field driven uniaxial anisotropy on the structural and the magnetic properties are discussed on the basis of reduction in strain at the Ta/Ni–Fe interface.

Self-Assembled On-Chip-Integrated Giant Magneto-Impedance Sensorics.

A novel method relying on strain engineering to realize arrays of on-chip-integrated giant magneto-impedance (GMI) sensors equipped with pick-up coils is put forth. The geometrical transformation of an initially planar layout into a tubular 3D architecture stabilizes favorable azimuthal magnetic domain patterns. This work creates a solid foundation for further development of CMOS compatible GMI sensorics for magnetoencephalography.

Enhancement of magnetic domain topologies in Co/Pt thin films by fine tuning the magnetic field path throughout the hysteresis loop

We have studied the influence of magnetic history on the topology of perpendicular magnetic domains in a thin ferromagnetic film made of [Co(8Å)/Pt(7Å)]50 multilayers. More specifically, we have followed the morphological changes in the domain pattern when applying a magnetic field perpendicular to the layer, throughout minor and major magnetization loops, and in the resulting remanent state. We carried out this study by using MFM microscopy with an in-situ magnetic field. We find that the morphology of the magnetic domain pattern is greatly influenced by the magnetic history of the material and that some features, such as the degree of bubbliness (i.e., the extent of bubble domain formation) and density of isolated domains can be enhanced by fine tuning the magnetic field path within the major hysteresis loop towards different remanent states. In particular, we see how hysteresis is correlated to irreversible changes in the domain morphology. More interestingly, we find that the magnetic domain morphology at remanence can be changed from an interconnected labyrinthine stripe state to a state of many separated bubble domains by fine tuning the magnitude of the field previously applied to the material. These results agree well with other findings, such as the magnetic reversal behavior and magnetic memory effects in Co/Pt multilayers, and provide opportunities for potential technological applications.

Buffer influence on magnetic dead layer, critical current, and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magnetic anisotropy fields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights.

Coarsening dynamics driven by vortex-antivortex annihilation in ferromagnetic Bose-Einstein condensates

In ferromagnetic Bose-Einstein condensates (BECs), the quadratic Zeeman effect controls magnetic anisotropy, which affects on magnetic domain pattern formation. While the longitudinal magnetization is dominant (similar to the Ising model) for a negative quadratic Zeeman energy, the transverse magnetization is dominant (similar to the XY model) for a positive one. When the quadratic Zeeman energy is positive, the coarsening dynamics is driven by vortex-antivortex annihilation in the same way as the XY model. However, due to superfluid flow of atoms, there exist several combinations of vortex-antivortex pairs in ferromagnetic BECs, which makes the coarsening dynamics more complicated than that of the XY model. We propose a revised domain growth law, which is based on the growth law of the two-dimensional XY model, for a two-dimensional ferromagnetic BEC with a positive quadratic Zeeman energy.

Effects of exchange randomness on two-dimensional magnetic domain pattern formation

Magnetic domain pattern formation is known to be influenced by structural disorder. We perform numerical simulations using a model of two-dimensional magnetic domain pattern formation focusing on effects of exchange randomness. The model is a scalar model with exchange and dipolar interactions, which includes disorder in the exchange interactions. Morphological change of the patterns with the increase in the disorder is observed. The distribution of the local magnetization becomes broader with the increase of the disorder. For a definite realization of the randomness, many patterns can appear.

Influence of Magnetostriction on Cross-Sectional Magnetic Properties in Bilayered Ribbons

This paper is devoted to the surface and cross-sectional microstructural and magneto-optical investigations of the bilayered (BL) CoFeCrSiB-based ribbon of dissimilar Co/Fe content in the layers and to the comparison with the CoSiB/FeSiB ribbon, both prepared by planar flow casting. It is shown that the interface properties are strongly influenced by chemical compositions of the layers and mainly by the magnetostriction coefficients. This results in different magnetic domain patterns in the layers and across the interlayer and their changes with applied magnetic field intensity. While in the BL sample of a similar layer composition, the magnetic domains concentrate inside the layers, at the sample with completely different layer composition, the domains cross the interlayer.

Direct Magnetic Domain Observation of Magnetization Reversal With Pre-Existing Nucleation Sites in Co/Pt Multilayer

Time-dependent magnetic domain patterns of Co/Pt multilayer with a perpendicular magnetic anisotropy has been directly observed by a magneto-optical Kerr microscopy. From our direct domain observation, it is revealed that, when a negative exposure field has been applied after positively saturating the film first, the number of pre-existing nucleation sites decreases as a strength and an applied time of the exposure field increase. It was also observed that pre-existing nucleation sites can speed up the magnetization reversal process by two orders of magnitude, where a strong correlation between the number of nucleation sites and the half-reversal time is found.

Vortex structures and magnetic domain patterns in the superconductor/ferromagnet hybrid bilayer

Superconducting vortices and magnetic domain patterns’ evolution in the superconductor-ferromagnet (SC/FM) hybrid bilayer are investigated within the Ginzburg—Landau (GL) theory of superconductivity, in combination with the Landau—Lifshitz—Gilbert (LLG) equation of ferromagnetism. Magnetic domain patterns in the ferromagnetic thin film and the vortices’ nucleation in the superconducting layer for the hybrid bilayer, subjected to perpendicular magnetic fields, are obtained by numerical simulations. A dynamical evolution picture of the magnetic domain patterns and the associated superconducting vortices’ nucleation are clearly shown. The effect of geometry parameters and physical parameters on the magnetic domain and superconducting vortex evolution are discussed. The magnetization curve of the SC film has also been illustrated. We found that the vortex dynamic behavior of the superconducting film changes substantially, and the correlated magnetic hysteresis loss is significantly reduced due to the presence of the ferromagnetic thin layer. In addition, the spontaneous vortex-antivortex (V-AV) pairs’ nucleation in the hybrid bilayer are investigated.