Stripe Domain Pattern Research Articles

Dynamics of domain growth driven by dipolar interactions in a perpendicularly magnetized ultrathin film

Measurements of the ac magnetic susceptibility of perpendicularly magnetized Fe/2ML Ni/W(110) ultrathin films show a clear signature of the dynamics of domain growth and domain density changes in the striped domain pattern that this system supports. The susceptibility peak measured at different constant heating rates in the range 0.20 K/s < R < 0.70 K/s shifts to higher temperature as the heating rate is increased. Analysis using a relaxation model demonstrates quantitatively that the dynamics is driven by a non-equilibrium domain density at (nearly) zero field (i.e. by dipole interactions), and that the temperature shift is due to a response time determined by the pinning of local domain wall segments by structural defects. The fundamental time scale for relaxation of the domain density driven by dipole interactions is of order 10^5 times slower than the fundamental time scale for an individual Barkhausen step driven by an applied field. The increase in the fundamental time scale reflects the relative size of dipole and Zeeman energies, and the need for the correlated motion of many local domain wall segments to affect domain growth.

Ferroelectric BaTiO3 Nanowires by a Topochemical Solid-State Reaction

The possible existence of a new kind of ferroelectric order and the need to explore domain arrangement in ferroelectric nanostructures has stimulated an increasing activity on the growth of ferroelectric nanowires. In the present study, single crystal BaTiO3 nanowires with tetragonal structure were obtained by an original solid-state process using layered titania nanowires coated with BaCO3 nanocrystals as reactive templates. Formation of BaTiO3 occurs at 700 °C by a topochemical reaction. Consequently, the initial morphology of the titania nanowires is retained in the final product. Piezoresponse force microscopy measurements show a strong piezoactivity and stripe domain patterns with domain width of 20−50 nm, predominant in-plane response and 90° domain walls. The proposed synthesis method is quite general and might be adapted to the fabrication different ferroelectric and nonferroelectric oxide nanowires.

Stripe domains and spin reorientation transition in Fe78B13Si9 thin films produced by rf sputtering

Magnetic thin films have been obtained by rf sputtering from an amorphous Fe78B13Si9 target. The samples have been produced with thickness t ranging in the interval 25–1000 nm. Microstructural investigations indicate that the films have different microstructures varying from fully amorphous to partially nanocrystalline with increasing t. Magnetic hysteresis loops have been measured by means of high-sensitive magnetometry. A tailorable spin reorientation transition (SRT) from in-plane single-domain-like to out-of-plane multidomain state with increasing film thickness was observed. Magnetic force microscopy images have been obtained for all samples indicating that for t≤80 nm the magnetization lies in the film plane. For larger thickness, a stripe domain pattern has been observed, indicating the presence of a magnetic anisotropy axis perpendicular to the film plane. In this work, SRT and stripe domain structure have been studied as a function of thickness and sample microstructure.

Guiding superconducting vortices with magnetic domain walls

We demonstrate a unique prospect for inducing anisotropic vortex pinning and manipulating the directional motion of vortices by using the stripe domain patterns of a uniaxial magnetic film in the superconducting/ferromagnetic hybrid. Our observations can be described by a model, which considers interactions between magnetic charges of vortices and surface magnetic charges of domains resulting in the enhanced pinning of vortices on domain walls.

Reversible magnetic domain-wall motion under an electric field in a magnetoelectric thin film

We report direct microscopic measurements that confirm the magnetic stripe-domain patterns can be reversibly changed under an electric field due to the converse magnetoelectric effect in a bilayer thin film ferromagnetic-Ni/ferroelectric-lead zirconate titanate (100nm∕1.28μm) heterostructure. Electric field-induced curving, bending, branching, and elongation of magnetic stripe-domain patterns in the Ni layer are observed with the use of magnetic force microscopy. Upon removal of the electric field, the magnetic stripe-domain patterns return to their original configuration, i.e., reversible.

Transport of Loaded and Unloaded Microcarriers in a Colloidal Magnetic Shift Register

We demonstrate the dispersion free digital transport of emulsion droplets and biological cells in an aqueous solution using paramagnetic colloidal particles above a uniaxial magnetic garnet film. Magnetic modulations above the stripe domain pattern induce a step-wise transport of paramagnetic particles dispersed in water and deposited on the surface of the film. Capillary or hydrodynamic interactions are then used to couple the cargo to the paramagnetic beads. We achieve full control of the cargo motion up to velocities in the 100 microm/s range.

Curvature Driven Transport of Mouse Macrophages in a Pulsating Magnetic Garnet Film Ratchet

Magnetic fields varying on the colloidal length scale are used for the directed transport of magnetically labeled biological cells. The transport is achieved by using the ratchet effect which relies on an asymmetric, symmetry broken periodic potential where nonequilibrium fluctuations or oscillations generate a net cell current. Ferrofluid ingested mouse macrophages were placed on a magnetic garnet film with alternating stripe domain patterns, and a pulsating magnetic potential is provided by superposing an oscillating magnetic field normal to the film. The symmetry of the resulting periodic stripe potential is broken locally by the curvature of the stripes. We show, both experimentally and theoretically, the curvature of such stripes required for inducing directed transport of the macrophages in the ratchet. This may be useful for microfluidic devices such as a digital colloidal shift register for magnetically labeled biological cells.

Spin-polarized scanning tunneling microscopy and spectroscopy of ferromagnetic Dy(0001)/W(110) films

Spin-polarized scanning tunneling microscopy and spectroscopy (SP-STS) are employed to investigate the contrast mechanism and the magnetic structure of Dy films epitaxially grown on W(110). While relatively complicated tip preparation procedures were necessary in the past, we now obtain magnetic contrast by bringing the tip in gentle contact with a ferromagnetic Dy film. Maximum contrast is observed at bias voltages around $\ensuremath{-}0.9\phantom{\rule{0.3em}{0ex}}\mathrm{V}$. Since highly polarized sample states are not available at the corresponding binding energy, we suggest that an unoccupied tip state is responsible for the strong magnetic contrast. SP-STS measurements show three-, four-, or sixfold magnetic contrast. This result can be explained by random azimuthal orientations of the tip magnetization with respect to the sample's easy axis. Images of the magnetic domain structure show a stripe domain pattern which consists of about $40\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ wide domains, the magnetization directions of which alternate by 60\ifmmode^\circ\else\textdegree\fi{}. This result is a clear proof that the Dy(0001) surface exhibits ferromagnetic order. The domain walls are identified as N\'eel walls with a width of $2\char21{}5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.

Ferroelectric domain periodicities in nanocolumns of single crystal barium titanate

A focused ion beam microscope has been used to mill rectangular “picture-frame” shapes from single crystal barium titanate. The lengths of the sides of the picture frames were of the order of 3–5μm, while the side width and thickness dimensions were of the order of 100–500nm. Such aspect ratios meant that each of the frame sides approximates to a column with rectangular cross section. Scanning transmission electron microsopy was used to characterize the ferroelectric domain configurations associated with these nanocolumns. It was found that conventional stripe domain patterns occurred in all cases, down to columnar cross-section sizes of the order of ∼100×100nm2. Despite the geometry of the columns rendering the ferroelectric as shape constrained in two dimensions, the domain periodicity was only noticeably sensitive to variations in the magnitude of one of those dimensions. Such observations were rationalized using arguments based on those used by Kittel [Phys. Rev. 70, 965 (1946)] and Mitsui and Furuichi [Phys. Rev. 90, 193 (1953)] for predicting the equilibrium domain periodicities in macroscopic slabs of ferroic material.

X-ray resonant magnetic scattering study of magnetic stripe domains ina−GdFethin films

X-ray resonant magnetic scattering (XRMS) has been used to investigate the structure of magnetic stripe domain patterns in thin amorphous GdFe films. Under the influence of a perpendicular magnetic field, the scattered intensity displays a smooth transition from a structure factor of correlated stripes to the form factor of isolated domains. We derive a quite general expression that relates the total scattered intensity of XRMS to the absolute value of the magnetization. Furthermore, we compare our results for the domain period with domain theory. We obtain good agreement for prealigned stripes, but disorder tends to lead to an overestimation of the period measured with XRMS.

High-frequency dynamics of Co/Fe multilayers with stripe domains

Within the framework of two-dimensional (2D) numerical micromagnetic simulations, the equilibrium magnetization configuration and the high-frequency (0.1–30 GHz) linear response of Co/Fe multilayers have been investigated in detail. Due to the perpendicular anisotropy of Co layers, a stripe domain pattern can develop through the whole multilayer, the characteristics of which depend on the magnitude of the perpendicular anisotropy, the respective thicknesses of Co and Fe layers and the number of Co/Fe bilayers in the stack. One of the most striking features associated with the layering effect is the ripening aspect of the static magnetization configuration across the multilayers which induces complicated dynamic susceptibility spectra including surface modes and volume modes strongly confined within the inner Fe layers. The effect of the cubic magnetocrystalline anisotropy of Fe layers and the influence of a nonuniform perpendicular magnetic anisotropy within the Co layers on the static and dynamic magnetic properties of Co/Fe multilayers are then analyzed quantitatively.

Influence of shearing process on domain structure and magnetic properties of non-oriented electrical steel

The influence of shearing on the magnetic properties and domain structure of 0.5 mm thick non-oriented electrical steel was studied. In the region from 1 to 1.4 mm from the sheared edge, a striped domain pattern that indicated the existence of elastic strain was observed. From the degradation tendency of flux density with respect to shearing width, the width of the degraded region near the edge increased as the magnetic field decreased. These results suggested that the change in the flux density at high magnetic fields over 300 A/m were mainly dependent on the characteristics of the edge vicinity where the domain pattern was influenced by shearing.

Lock in of magnetic stripe domains to pinning lattices produced by focused ion-beam patterning

With focused ion-beam irradiation it is possible to engineer the anisotropy of magnetic films on nanometer length scales. We used this technique to write square lattices of artificial domain-wall pinning centers in a perpendicular anisotropy GdFe film displaying a well-defined stripe domain pattern. We observe a clear lock in of the intrinsic meandering stripe pattern to the pinning lattices, resulting in highly ordered domain patterns. We find that at remanence the dots pin the domain walls, while in perpendicular applied magnetic fields they host the down domains.

Investigation of magnetic domains in Ni–Mn–Ga alloys with a scanning electronmicroscope

The magnetic domains of martensite have been investigated with a scanning electronmicroscope in three Ni–Mn–Ga alloys with five-layered, seven-layered and non-layered (T)martensite structure. Type I magnetic contrast provides an overview of the domain pattern.This contrast arises from the stray field of the specimen and it is observed in asecondary-electron image. The type II magnetic contrast of a backscattered electron imagegives the detailed magnetic microstructure together with the crystal morphology. A stripedomain pattern is formed in all the alloys when there is one dominant martensite variantin the sample. The second minor variant might be distorted due to interactionwith the magnetic domain structure of the major variant. The mechanism of thedeformation is not entirely clear and a tentative explanation for this deformation issuggested.

Sub-nanosecond resolution x-ray magnetic circular dichroism photoemission electronmicroscopy of magnetization processes in a permalloy ring

Fast magnetization processes in a microstructured permalloy ring with80 µm o.d. and 30 nm thickness have been observed by photoemission electron microscopyexploiting x-ray magnetic circular dichroism as the magnetic contrast mechanism.As a high speed probe we employed synchrotron radiation pulses at the ESRF(Grenoble) operated in 16-bunch mode, yielding photon pulses of 105 ps FWHM witha period of 176 ns. Fast magnetic field pulses have been generated by means ofcurrent pulses through coplanar waveguides with the magnetic structure beinglithographically prepared on their surface. A stroboscopic pump–probe set-up witha variable time delay between the field pulse and photon pulse allowed us totake snapshots of the dynamic response of the magnetic domain structure. Weobserved coherent magnetization rotation during the leading edge part of the fieldpulse, the formation of a characteristic domain pattern (‘onion state’) in theplateau region of the pulse and the fast formation of a striped domain pattern(incoherent magnetization rotation) during the trailing edge part of the field pulse. Anumerical simulation confirmed essential features of the stroboscopic image series.

Electrical transport study of exchange bias in patterned Co/CoO bilayers

A stripe pattern of antiferromagnetic CoO is used to locally exchange bias a ferromagnetic Co film. Magnetization and magnetoresistance measurements enable to investigate the resulting change in the magnetization and the magnetic hysteresis behavior. The results demonstrate that a regular antiparallel stripe domain pattern can be created. Moreover, it is possible to tune the shape of the magnetic hysteresis by properly choosing the geometry of the CoO template.

Measurement of the Magnetostriction Constant of Bi-Doped Garnets by Optical Observation of Stress-Induced Stripe Domains

In this paper, we report on the optical investigation of magnetic microstructures in Bi substituted garnet thin films grown by epitaxial deposition on (111)-oriented gallium gadolinium garnet substrates. The specimens are magnetically diluted with Ga ions. By using a technique based on the bending of the thin film, the appearance of a straight stripe domain pattern is observed. The changes in this stripe pattern due to external applied in-plane and out-of-plane fields are correlated to those induced by a known applied stress. We show that this method can be used to compute the magnetostriction coefficient /spl lambda//sub 111/ of the material. One important advantage of this method is that it allows a real-time optical observation of the manifestations of magnetoelastic interactions.

Magnetic anisotropy of aligned magnetic stripe domains in FePd studied by soft x-ray resonant magnetic scattering, magnetic force microscopy and micromagnetic modeling

FePd thin-film samples with different perpendicular magnetic anisotropies have been studied with magnetic force microscopy (MFM), micromagnetic calculations and soft x-ray resonant magnetic scattering (SXRMS). The competition between perpendicular magnetic anisotropy (PMA) and shape anisotropy leads to the formation of highly ordered stripe domain patterns with a magnetization component perpendicular to the film plane. The magnetic stripes with a period of ∼100 nm, which are seen in the MFM images and can be modeled by micromagnetic calculations, give rise to magnetic peaks in the diffraction pattern. Closure domains occur in samples with a low to medium PMA, while a high PMA inhibits their formation. The in-plane magnetization component of the closure domains is not observable with MFM. In the presence of closure domains the interference between the scattering amplitudes in SXRMS from perpendicular and in-plane magnetized domains gives rise to a circular dichroism in the transverse geometry, where the scattering plane is along the stripes. We also recorded the magnetic speckle pattern from an 8 μm FePd wire using coherent x-rays and CCD detection. A high degree of coherence was obtained as evidenced from the observed intensity fluctuations. The speckle pattern can in principle provide information about the local disorder of the magnetic stripe domains.

Magnetic anisotropy of aligned magnetic stripe domains in FePd studied by soft x-ray resonant magnetic scattering, magnetic force microscopy and micromagnetic modeling*1

FePd thin-film samples with different perpendicular magnetic anisotropies have been studied with magnetic force microscopy (MFM), micromagnetic calculations and soft x-ray resonant magnetic scattering (SXRMS). The competition between perpendicular magnetic anisotropy (PMA) and shape anisotropy leads to the formation of highly ordered stripe domain patterns with a magnetization component perpendicular to the film plane. The magnetic stripes with a period of ∼100 nm, which are seen in the MFM images and can be modeled by micromagnetic calculations, give rise to magnetic peaks in the diffraction pattern . Closure domains occur in samples with a low to medium PMA, while a high PMA inhibits their formation. The in-plane magnetization component of the closure domains is not observable with MFM. In the presence of closure domains the interference between the scattering amplitudes in SXRMS from perpendicular and in-plane magnetized domains gives rise to a circular dichroism in the transverse geometry, where the scattering plane is along the stripes. We also recorded the magnetic speckle pattern from an 8 μm FePd wire using coherent x-rays and CCD detection. A high degree of coherence was obtained as evidenced from the observed intensity fluctuations. The speckle pattern can in principle provide information about the local disorder of the magnetic stripe domains.

Strain-induced magnetic stripe domains in La0.7Sr0.3MnO3 thin films

We have investigated magnetic microstructures of magnetoresistive La0.7Sr0.3MnO3 (LSMO) thin films. Magnetic images are strongly dependent on structural strain induced by the substrates. The LSMO film on SrTiO3 dominated by tensile stress effect displays a feather-like pattern, whereas LSMO films on LaAlO3 and NdGaO3 substrates under compressive stress show stripe domains. In particular, the magnetic image of the film on NdGaO3 reveals distinctive straight stripe domain patterns on the order of about 120 nm, suggesting the presence of a sizable out-of-plane magnetization. The ordering of the stripe domains is also sensitive to the field direction.