Magnetic Domains In Thin Films Research Articles

A continuum theory for stripe-shaped magnetic domains in thin films

Starting from a potential-based kinematical description of continuously distributed stripe-shaped domain walls, a mesoscopic potential is derived through an averaging procedure. The resulting mesoscopic theory is formulated in terms of a few fields with physically meaningful microscopic interpretation. Based on a phenomenological closure-domain extension, a constrained energy minimization principle is introduced. A monolithic finite-element based numerical solution algorithm is proposed. Based on a consistent linearization of the numerical algorithm, quadratic convergence is obtained for the nonlinear solution procedure. A first simple examination of the theory is undertaken by simulating a thin film with spatially and temporally non-constant effective anisotropy. The results are found to be consistent with analytical predictions.

Spontaneous Formation of Ordered Magnetic Domains by Patterning Stress.

The formation of ordered magnetic domains in thin films is important for the magnetic microdevices in spin-electronics, magneto-optics, and magnetic microelectromechanical systems. Although inducing anisotropic stress in magnetostrictive materials can achieve the domain assembly, controlling magnetic anisotropy over microscale areas is challenging. In this work, we realized the microscopic patterning of magnetic domains by engineering stress distribution. Deposition of ferromagnetic thin films on nanotrenched polymeric layers induced tensile stress at the interfaces, giving rise to the directional magnetoelastic coupling to form ordered domains spontaneously. By changing the periodicity and shape of nanotrenches, we spatially tuned the geometric configuration of domains by design. Theoretical analysis and micromagnetic characterization confirmed that the local stress distribution by the topographic confinement dominates the forming mechanism of the directed magnetization.

Vectorial, non-destructive magnetic imaging with scanning tunneling microscopy in the field emission regime

When a scanning tunneling microscope is operated at tip-target distances ranging from few nanometers to few tens of nanometers (Fowler-Nordheim or field emission regime), a new electronic system appears, consisting of electrons that escape the tip-target junction. If the target is ferromagnetic, this electronic system is spin polarized. Here, we use these spin polarized electrons to image magnetic domains in thin films. As two components of the spin polarization vector are detected simultaneously, the imaging of the local magnetization has vectorial character. The tip is nonmagnetic, i.e., the magnetic state of the target is not perturbed by the act of probing. We expect this spin polarized technology, which scales down scanning electron microscopy with polarization analysis by bringing the source of primary electrons in close proximity to the target, to find its main applications in the imaging of noncollinear, weakly stable spin excitations.

A study of magnetic domains in thin films from FM and AFM interactions

This work introduces a combination of three factors for explaining the possible causes of “magnetic domains” presented in experimental reports. The first factor is the combination of a ferromagnetic (FM) interaction between first neighbors with an antiferromagnetic (AFM) interaction at relatively long distances. The second factor is the presence of surface anisotropy in a direction perpendicular to the film; finally, the third factor is the effect of the thickness. The classic Heisenberg model with cubic anisotropy and uni-axial surface anisotropy was studied through Monte Carlo simulations using the Metropolis algorithm. The results show different magnetic domains according to the thickness and surface anisotropy intensity. The distance at which the interaction becomes AFM is a crucial aspect for explaining the magnetic behaviors.

Remote teaching experiments on magnetic domains in thin films

We describe our experience in building a remote laboratory for teaching magnetic domains. Fulfilling the proposed on-line experiments, students can observe and study magnetization processes that are often difficult to explain with written material. It is proposed that networks of remotely accessible laboratories could be integrated in the Global Laboratory which could make research and education closer as well as disseminate knowledge and research results to a non-expert audience.

Polarized neutron reflectivity and scattering studies of magnetic heterostructures

The current interest in the magnetism of ultrathin films and multilayers is drivenby their manifold applications in the magneto-and spin-electronic areas, forinstance as magnetic field sensors or as information storage devices. In this regard,there is a large interest in exploring spin structures and spin disorder at theinterface of magnetic heterostructures, to investigate magnetic domains in thinfilms and superlattices, and to understand remagnetization processes of variouslaterally shaped magnetic nanostructures. Traditionally neutron scattering hasplayed a dominant role in the determination of spin structures, phase transitionsand magnetic excitations in bulk materials. Today, its potential for theinvestigation of thin magnetic films has to be redefined. Polarized neutronreflectivity (PNR) at small wavevectors can provide precise information onthe magnetic field distribution parallel to the film plane and on layerresolved magnetization vectors. In addition, PNR is not only sensitiveto structural interface roughness but also to the magnetic roughness.Furthermore, magnetic hysteresis measurements from polarized smallangle Bragg reflections allows us to filter out correlation effects duringmagnetization reversals of magnetic stripes and islands. An overview isprovided on most recent PNR investigations of magnetic heterostructures.

Reconstruction of magnetization density in two-dimensional samples from soft X-ray speckle patterns using the multiple-wavelength anomalous diffraction method.

A non-destructive technique for imaging magnetic domains in thin films and two-dimensional magnetic structures using coherent soft X-ray scattering and the multiple-wavelength anomalous diffraction method (MAD) is proposed. The method exploits the strong energy dependence in the magnetic scattering amplitude for 3d transition metals near the L(2,3) absorption edges and 4f elements near the M(4,5) absorption edges. The phase information required in the reconstruction algorithm is derived from the interference between the charge and magnetic scattering amplitudes. Magnetic speckle patterns from the magnetic domain distribution in an artificially defined Fe thin film are used to demonstrate this reconstruction algorithm. Circularly and linearly polarized incident light are examined separately to investigate the effect of polarization on the capability of the method.

An effective-viscosity description of domain-wall motion in magnetic thin films with perpendicular anisotropy

The expansion of magnetic domains in thin films with perpendicular anisotropy is investigated. To determine the domain-wall-velocity as a function of the applied magnetic field a selfconsistent magnetic-viscosity approach is used. The main predictions of the theory are a linear behaviour in the moderately strong fields, a quasi-exponential behaviour for fields close to the propagation field, and a negative velocity for very small and negative fields. The predictions of the theory are compatible with domain-wall investigations on Au/Co/Au sandwiches.

Two types of performance of an isotropic cellular automaton: stationary (Turing) patterns and spiral waves

An isotropic cellular automaton containing only the crudest caricature of activator-inhibitor systems, is shown to be capable of producing stationary spatial structures (Turing patterns) in qualitative agreement with a variety of experiments in chemistry. Due to the isotropy of our automaton, we can obtain spots arranged in regular hexagons, a pattern that cannot be obtained with a classical square lattice. Labyrinthine stripes, like those observed in magnetic domains in thin films, are also obtained. Spiral waves are obtained upon increasing the radius of action of the activator relative to that of the inhibitor, as predicted by theory.

Observations of Magnetic Domains in Thin Films by Electron Holography with a Commercial TEM with FEG

Observations of Magnetic Domains in Thin Films by Electron Holography with a Commercial TEM with FEG

Thin-magnetic-film general-purpose uniform array based on controlled domain motion

Thin-film uniform arrays (UA's) are general purpose, easy to produce, and reliable even when implementing complex logic functions. The use of controlled domain motion in narrow channels of low coercive force, formed in a high-coercive-force film, may serve as the basis for the implementation of large uniform programmable logic arrays with memory which feature information storage immune to power supply failures, and the simplicity of logic and control implementation. In this paper, principles of UA design are considered. Attention is given to performing logic operations using the controllable movement of magnetic domains in thin films.

Magnetic Domains in Thin Films by the Faraday Effect

Magnetic Domains in Thin Films by the Faraday Effect

Magnetic Domains in Thin Films of Nickel-Iron

Magnetic Domains in Thin Films of Nickel-Iron