Ferromagnetic Domain Patterns Research Articles

Magnetoelectric transfer of a domain pattern.

The utility of ferroic materials is determined by the formation of domains and their poling behavior under externally applied fields. For multiferroics, which exhibit several types of ferroic order at once, it is also relevant how the domains of the coexisting ferroic states couple and what kind of functionality this might involve. In this work, we demonstrate the reversible transfer of a domain pattern between magnetization and electric-polarization space in the multiferroic Dy0.7Tb0.3FeO3. A magnetic field transfers a ferromagnetic domain pattern into an identical ferroelectric domain pattern while erasing it at its magnetic origin. Reverse transfer completes the cycle. To assess the generality of our experiment, we elaborate on its conceptual origin and aspects of application.

Phase Retrieval Algorithm based on Total Variation Regularization for Ferromagnetic Domain Patterns

Phase Retrieval Algorithm based on Total Variation Regularization for Ferromagnetic Domain Patterns

Phase Retrieval Algorithm based on Total Variation Regularization for Ferromagnetic Domain Patterns

Phase Retrieval Algorithm based on Total Variation Regularization for Ferromagnetic Domain Patterns

Readout of an antiferromagnetic spintronics system by strong exchange coupling of Mn2Au and Permalloy

In antiferromagnetic spintronics, the read-out of the staggered magnetization or Néel vector is the key obstacle to harnessing the ultra-fast dynamics and stability of antiferromagnets for novel devices. Here, we demonstrate strong exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits Néel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows us to benefit from the well-established read-out methods of ferromagnets, while the essential advantages of antiferromagnetic spintronics are only slightly diminished. We show one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain pattern. Conversely, alignment of the Permalloy magnetization reorients the Mn2Au Néel vector, an effect, which can be restricted to large magnetic fields by tuning the ferromagnetic layer thickness. To understand the origin of the strong coupling, we carry out high resolution electron microscopy imaging and we find that our growth yields an interface with a well-defined morphology that leads to the strong exchange coupling.

Magnetoelectric inversion of domain patterns.

The inversion of inhomogeneous physical states has great technological importance; for example, active noise reduction relies on the emission of an inverted sound wave that interferes destructively with the noise of the emitter1, and inverting the evolution of a spin system by using a magnetic-field pulse enables magnetic resonance tomography2. In contrast to these examples, inversion of a distribution of ferromagnetic or ferroelectric domains within a material is surprisingly difficult: field poling creates a single-domain state, and piece-by-piece inversion using a scanning tip is impractical. Here we report inversion of entire ferromagnetic and ferroelectric domain patterns in the magnetoelectric material Co3TeO6 and the multiferroic material Mn2GeO4, respectively. In these materials, an applied magnetic field reverses the magnetization or polarization, respectively, of each domain, but leaves the domain pattern intact. Landau theory indicates that this type of magnetoelectric inversion is universal across materials that exhibit complex ordering, with one order parameter holding the memory of the domain structure and another setting its overall sign. Domain-pattern inversion is only one example of a previously unnoticed effect in systems such as multiferroics, in which several order parameters are available for combination. Exploring these effects could therefore advance multiferroicstowardsnew levels of functionality.

Experimental evaluation of signal-to-noise in spectro-holography via modified uniformly redundant arrays in the soft x-ray and extreme ultraviolet spectral regime

We present dichroic x-ray lensless magnetic imaging by Fourier transform holography with an extended reference scheme via a modified uniformly redundant array (mURA). Holographic images of magnetic domains simultaneously generated by a single pinhole reference as well as by a mURA reference are compared with respect to the signal-to-noise ratio (SNR) as a function of exposure time. We apply this approach for spectro-holographic imaging of ferromagnetic domain patterns in Co/Pt multilayer films. Soft x-rays with wavelengths of 1.59 nm (Co L3 absorption edge) and 20.8 nm (Co M2,3 absorption edges) are used for image formation and to generate contrast via x-ray magnetic circular dichroism. For a given exposure time, the mURA-based holography allows to decouple the reconstruction SNR from the spatial resolution. For 1.59 nm wavelength, the reconstruction via the extended reference scheme shows no significant loss of spatial resolution compared to the single pinhole reference. In contrast, at 20.8 nm wavelength the single pinhole reveals some very intricate features which are lost in the image generated by the mURA, although overall a high-quality image is generated. The SNR-advantage of the mURA scheme is most notable when the hologram has to be encoded with few photons, while errors associated with the increased complexity of the reconstruction process reduce the advantage for high-photon-number experiments.

Enhancements of Faraday rotation through ferromagnetic domain matching in arrayed magneto-optic films

In linear arrays of optically probed bismuth-doped iron garnet films, the Faraday rotation signal produced by an external magnetic field is a complex function of film shapes, stacking geometries, optical path length, and insertion losses. Studies of arrayed responsivities under various configurations reveal a proximity coupling effect between ferromagnetic domains of adjacent films, which enhances Faraday rotation by minimizing demagnetization effects at the interfaces. The effect is activated by matching ferromagnetic domain patterns in adjacent films and has resulted in over a twofold improvement in detection sensitivities when the arrays were configured as polarimetric magneto-optic sensors.

Direct observations of ferromagnetic and antiferromagnetic domains in Pt/Co/Cr<sub>2</sub>O<sub>3</sub>/Pt perpendicular exchange biased film

By using focused soft X-rays, magnetic domain imaging based on X-ray magnetic circular dichroism (XMCD) measurements was performed on a Pt/Co/Cr2O3/Pt film that exhibits both perpendicular magnetic anisotropy and perpendicular exchange anisotropy. In the AC-demagnetized state, spatial distributions of the XMCD corresponding to the magnetic domains were clearly observed. In particular, ferromagnetic and antiferromagnetic magnetic domains were separately observed by tuning the photon energy to either the ferromagnetic Co L3 edge or the antiferromagnetic Cr L3 edge. The ferromagnetic domain pattern is similar to the ones previously reported for Co/Pt multilayers, and the ferromagnetic and antiferromagnetic domains are spatially coupled. The magnetization curve measured after cooling the sample, while maintaining the demagnetized state, exhibited positive and negative exchange biases simultaneously, which suggests that the exchange bias is determined on a domain-by-domain basis.

Domain-wall structure in thin films with perpendicular anisotropy: Magnetic force microscopy and polarized neutron reflectometry study

Ferromagnetic domain patterns and three-dimensional domain-wall configurations in thin CoCrPt films with perpendicular magnetic anisotropy were studied in detail by combining magnetic force microscopy and polarized neutron reflectometry with micromagnetic simulations. With the first method, lateral dimension of domains with alternative magnetization directions normal to the surface and separated by domain walls in 20-nm-thick CoCrPt films were determined in good agreement with micromagnetic simulations. Quantitative analysis of data on reflectometry shows that domain walls consist of a Bloch wall in the center of the thin film, which is gradually transformed into a pair of N\'eel caps at the surfaces. The width and in-depth thickness of the Bloch wall element, transition region, and N\'eel caps are found consistent with micromagnetic calculations. A complex structure of domain walls serves to compromise a competition between exchange interactions, keeping spins parallel, magnetic anisotropy orienting magnetization normal to the surface, and demagnetizing fields, promoting in-plane magnetization. It is shown that the result of such competition strongly depends on the film thickness, and in the thinner CoCrPt film (10 nm thick), simple Bloch walls separate domains. Their lateral dimensions estimated from neutron scattering experiments agree with micromagnetic simulations.

Temperature control of local magnetic anisotropy in multiferroic CoFe/BaTiO3

This paper reports on the temperature evolution of local elastic interactions between ferromagnetic CoFe films and ferroelectric BaTiO3 substrates. Polarization microscopy measurements indicate that growth-induced stripe domains in the CoFe films are preserved and strengthened during cooling and heating through the structural phase transitions of BaTiO3. Moreover, rotation of the magnetic easy axes at the tertragonal-to-orthorhombic transition (T = 278 K) and at T ≈ 380 K simultaneously switches the local magnetization of both uniaxial domains by 90°. Irreversible changes in the ferromagnetic domain pattern are induced when the room-temperature ferroelectric domain structure is altered after temperature cycling.

Effects of magnetic flux density and substrate temperature on Ni films prepared by means of unbalanced magnetron sputtering assisted by inductively coupled plasma

We prepared Ni films on glass substrates by means of Unbalanced Magnetron Sputtering Assisted by Inductively Coupled Plasma (UM-ICP). The effects of the magnetic flux density BC and the substrate temperature TS on their structures were investigated. We found that the surface grain size observed with an atomic force microscope became large as BC and TS increase. We also found that the (111) plane measured by X-ray diffraction was preferentially orientated on the films under BC=5 mT at TS=60°C. These indicate that the energetic particle bombardment under BC and the increase of TS promote the surface diffusion on the Ni films. The ferromagnetic domain patterns observed with a magnetic force microscope showed the stripe domain structure having the domain width increasing with increasing TS and the fractal dimension of 1.88.

Electric-field control of magnetic domain wall motion and local magnetization reversal

Spintronic devices currently rely on magnetic switching or controlled motion of domain walls by an external magnetic field or spin-polarized current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including enhanced functionality and low power consumption. Here we report on an approach to electrically control local magnetic properties, including the writing and erasure of regular ferromagnetic domain patterns and the motion of magnetic domain walls, in CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer from ferroelastic domains in ferroelectric media to continuous magnetostrictive films with negligible magnetocrystalline anisotropy. Optical polarization microscopy of both ferromagnetic and ferroelectric domain structures reveals that domain correlations and strong inter-ferroic domain wall pinning persist in an applied electric field. This leads to an unprecedented electric controllability over the ferromagnetic microstructure, an accomplishment that produces giant magnetoelectric coupling effects and opens the way to electric-field driven spintronics.

Mutual Ferromagnetic–Ferroelectric Coupling in Multiferroic Copper‐Doped ZnO

A mutual ferromagnetic and ferroelectric coupling (multiferroic behavior) in Cu‐doped ZnO is demonstrated via deterministic control of Cu doping and defect engineering. The coexistence of multivalence Cu ions and oxygen vacancies is important to multiferroic behaviors in ZnO:Cu. The samples show clear ferroelectric and ferromagnetic domain patterns. These domain structures may be written reversibly via electric and magnetic bias.

Observation of Higher Suppression of Superconducting Transition Temperature in YBa2Cu3O7−δ /La0.5Sr0.5CoO3 as Compared to YBa2Cu3O7−δ /La0.7Sr0.3MnO3 Bilayers

We report the experimental investigations of the suppression of superconductivity due to the pair breaking effect induced by ferromagnetic layer in YBa2Cu3O7−δ /La0.5Sr0.5CoO3 and YBa2Cu3O7−δ /La0.7Sr0.3MnO3 bi-layers fabricated by pulsed laser deposition. The current dependent electrical transport studies in the bilayers exhibit a significant reduction in the superconducting transition temperature in accord to I 2/3 law as compared to single YBa2Cu3O7−δ layer, and moreover the superconducting transition temperature in YBa2Cu3O7−δ /La0.7Sr0.3MnO3 bilayer is surprisingly found to be much larger than the YBa2Cu3O7−δ /La0.5Sr0.5CoO3. It appears that the current driven from a low spin polarization (−11%) material like La0.5Sr0.5CoO3 can also suppress the superconductivity to a larger extent. This indicates that the degree of spin polarization of the ferromagnetic electrode is not the only criteria to determine the suppression of superconductivity by pair breaking effect in superconductor/ferromagnet hybrid structures; rather the transparency of the interface for the spin polarization, the formation of vortex state due to the stray field of ferromagnetic layer and the ferromagnetic domain patterns might play significant roles to determine such effect.

Temperature evolution of anisotropic stress induced highly ordered stripe magnetic domains in [formula omitted] thin film on (110) [formula omitted] substrate

Highly ordered ferromagnetic (FM) domain patterns with out-of-plane magnetization have been observed in La 0.7Sr 0.3MnO 3 (LSMO) thin film on (110) NdGaO 3 (NGO). Crystal structure and strain state analyses show that this remarkable domain pattern originates from the in-plane anisotropic stress induced by the substrate. Magnetic force microscope (MFM) images at different temperatures show that the FM domain contrast gradually decreases upon heating and disappears around the transition temperature. The root mean square (RMS) of the MFM images coincides with the resistivity measurement, suggesting that the change in resistivity with temperature is mainly due to carrier scattering by thermal spin fluctuation.

Asymmetric magnetization reversal in a single exchange-biased micro bar

The asymmetric magnetization reversal is studied in a single exchange-biased microbar of 1.5×13μm2 with anisotropic magnetoresistance and magnetic force microscopy. The asymmetric hysteresis loop of CoFe∕CrMnPt shows a repeatable rotation process, followed by an irreversible nucleation process that is marked by jumps in the magnetoresistance. The induced unidirectional anisotropy enhances the rotation process in one branch of the hysteresis loop, followed by a sped up nucleation process. Imprinted ferromagnetic domain patterns left behind by the antiferromagnet are observed after the nucleation process occurred but before complete saturation is reached.

Magnetic state ofLa1.36Sr1.64Mn2O7probed by magnetic force microscopy

We have investigated the ferromagnetic (FM) domain structure of a single-crystal bilayered manganite ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ $(x=0.32)$ by using low-temperature magnetic force microscopy. We observed that below $65\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the FM domains form stable treelike patterns with out-of-plane magnetization. With increasing temperature, the FM domain patterns gradually change in the form of domain wall motion. Above $80\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the FM domain patterns change more and more with each temperature step. The magnetization changes from the out-of-plane to an in-plane direction around $88\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The in-plane FM domains almost completely disappear near the Curie temperature of this sample $({T}_{C}\ensuremath{\approx}110\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, where the resistivity exhibits a sharp increase. We also observed large changes in the magnetic structures upon thermal cycling. We concluded that the formation of FM domains at low temperatures $(T<80\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ is determined by the energy associated with surface magnetic free poles and domain walls. At high temperatures $(80\phantom{\rule{0.3em}{0ex}}\mathrm{K}<T<{T}_{C})$, the two-dimensional FM fluctuations in the basal plane may also play an important role in forming the domain structures. The evolution of the FM domain patterns with temperature coincides with the change in resistivity.

Ferromagnetic and twin domains in LCMO manganites

Ferromagnetic and twin domains in lightly Ca-doped La 1 - x Ca x MnO 3 single crystals have been visualized and investigated by means of the magneto-optical technique. Both types of domains became visible below the Curie temperature. The dominant structures seen in applied magnetic field are associated with magneto-crystalline anisotropy and twin domains. In a marked difference to the twin domains which appear only in applied magnetic field, ferromagnetic domains show up in zero applied field and are characterized by oppositely oriented spontaneous magnetization in adjacent domains. Ferromagnetic domains take form of almost periodic, corrugated strip-like structures. The corrugation of the ferromagnetic domain pattern is enforced by the underlying twin domains.

Ferromagnetic domain patterns of Ni and Fe polycrystals in the course of the magnetic hysteresis loop

Origin and change of ferromagnetic domain patterns on the surface of polycrystalline Ni and Fe specimens in the course of the magnetic hysteresis loop have been investigated by means of the Bitter colloid technique. Comparing Ni and Fe, similarities and dissimilarities of typical domain patterns and their changes are reported.

Electrodeposition of Thin Magnetic Permalloy Films

A citrate‐complexed nickel‐iron electrolyte which has a long useful plating life from the point of view concerning the magnetic properties of the plated films and a better plating efficiency compared to the conventional baths has been used to plate thin magnetic films of 80:20 nickel‐iron from about 150 to about 8000Aå. The magnetic properties, like the coercive force and the anisotropy field , were determined at a known thickness as a function of current density, pH, temperature, and the concentration of citrate ion and the plating conditions optimized. The ferromagnetic domain patterns observed by the Bitter technique as a function of thickness show the same behavior as those observed in evaporated films. Internal stress measurements made as a function of thickness, current density, and temperature show that both the current density and the temperature have significant effect on stress. Photomicrographs of deposits obtained at a wide range of current density show the differences in the structure of the deposits.