Domain wall mobility in nanowires: Transverse versus vortex walls

Wieser, Robert; Nowak, Ulrich; Usadel, K. D.

doi:10.1103/physrevb.69.064401

Cited by 122 publications

(120 citation statements)

References 8 publications

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“…Results of our simulations and previous results in wires 7,8,9,10 show three main idealized types of MR, where M changes from one of its two energy minima (M = M 0ẑ , with energy E F ) to the other (M = −M 0ẑ , with energy E F ) by a path such that the energy barrier is the difference between the energy maximum (E max ) and the energy minimum. These mechanisms are illustrated in Fig.…”

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confidence: 99%

“…An important problem is to establish the way and conditions for reversing the orientation of the magnetization. Although the reversal process is well known for ferromagnetic nanowires, 6,7,8,9,10 the equivalent phenomenon in nanotubes has been poorly explored so far in spite of some potential advantages over solid cylinders. Nanotubes exhibit a core-free magnetic configuration leading to uniform switching fields, guaranteeing reproducibility, 4,5 and due to their low density they can float in solutions making them suitable for applications in biotechnology (see [1] and refs.…”

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Reversal modes in magnetic nanotubes

Landeros

Allende

Escrig

et al. 2007

Applied Physics Letters

217

200

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The magnetic switching of ferromagnetic nanotubes is investigated as a function of their geometry. Two independent methods are used: Numerical simulations and analytical calculations. It is found that for long tubes the reversal of magnetization is achieved by two mechanism: The propagation of a transverse or a vortex domain wall depending on the internal and external radii of the tube.During the last decade, interesting properties of magnetic nanowires have attracted great attention. Besides the interest in their basic properties, there is evidence that they can be used in the production of new devices. More recently magnetic nanotubes have been grown 1,2,3,4 motivating a new research field. Magnetic measurements, 3 numerical simulations 4 and analytical calculations 5 on such tubes have identified two main states: an in-plane magnetic ordering, namely the fluxclosure vortex state, and a uniform state with all the magnetic moments pointing parallel to the axis of the tube. An important problem is to establish the way and conditions for reversing the orientation of the magnetization. Although the reversal process is well known for ferromagnetic nanowires, 6,7,8,9,10 the equivalent phenomenon in nanotubes has been poorly explored so far in spite of some potential advantages over solid cylinders. Nanotubes exhibit a core-free magnetic configuration leading to uniform switching fields, guaranteeing reproducibility, 4,5 and due to their low density they can float in solutions making them suitable for applications in biotechnology (see [1] and refs. therein).Let us consider a ferromagnetic nanotube in a state with the magnetization M along the tube axis. A constant and uniform magnetic field is then imposed antiparallel to M. After some delay time the magnetization reversal (MR) will start at any end. MR or magnetic switching can occur by means of different mechanisms, depending on the geometrical parameters of the tube. In this paper we will focus on the reversal process by means of two different but complementary approaches: numerical simulations and analytical calculations. Their mutual agreement sustains the results reported in this study.Numerical Simulations. Geometrically, tubes are characterized by their external and internal radii, R and a respectively, and height, H. It is convenient to define the ratio β ≡ a/R, so that β = 0 represents a solid cylinder and β → 1 correspond to a very narrow tube. The internal energy, E, of a nanotube with N magnetic moments can be written aswhere E ij is the dipolar energy given by E ij = µ i · µ j − 3(µ i ·n ij )(µ j ·n ij ) /r 3 ij , with r ij the distance between the magnetic moments µ i and µ j ,μ i the unit vector along the direction of µ i andn ij the unit vector along the direction that connects µ i and µ j . J ij = J is the exchange coupling constant between nearest neighbors and J ij = 0 otherwise. E a = − N i=1 µ i · H a is the contribution of the external magnetic field. In this paper we are interested in soft magnetic materials, in which case anisotropy can be s...

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mentioning

confidence: 99%

mentioning

confidence: 99%

Reversal modes in magnetic nanotubes

Landeros

Allende

Escrig

et al. 2007

Applied Physics Letters

217

200

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“…For devices, the detailed spin structure of a domain wall is crucial for setting the relevant physical properties such as the dynamic behaviour including domain wall velocities and critical current densities for current induced domain wall motion [11][12][13][14][15] and hence this can determine the ultimate performance and attainable data storage densities. Two types of domain wall are favored in such nanoscale planar wires; in general, in narrower and thinner structures, the transverse domain wall is observed where the magnetization rotates by 180 • via a roughly triangular region where the magnetization is directed off-axis to the wire [11][12][13]16].…”

Section: Introductionmentioning

confidence: 99%

Domain wall spin structures in mesoscopic Fe rings probed by high resolution SEMPA

Krautscheid¹,

Reeve²,

Lauf³

et al. 2016

J. Phys. D: Appl. Phys.

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We present a combined theoretical and experimental study of the energetic stability and accessibility of different domain wall spin configurations in mesoscopic magnetic iron rings. The evolution is investigated as a function of the width and thickness in a regime of relevance to devices, while Fe is chosen as a material due to its simple growth in combination with attractive magnetic properties including high saturation magnetization and low intrinsic anisotropy. Micromagnetic simulations are performed to predict the lowest energy states of the domain walls, which can be either the transverse or vortex wall spin structure, in good agreement with analytical models, with further simulations revealing the expected low temperature configurations observable on relaxation of the magnetic structure from saturation in an external field. In the latter case, following the domain wall nucleation process, transverse domain walls are found at larger widths and thicknesses than would be expected by just comparing the competing energy terms demonstrating the importance of metastability of the states. The simulations are compared to high spatial resolution experimental images of the magnetization using scanning electron microscopy with polarization analysis to provide a phase diagram of the various spin configurations. In addition to the vortex and simple symmetric transverse domain wall, a significant range of geometries are found to exhibit highly asymmetric transverse domain walls with properties distinct from the symmetric transverse wall.Simulations of the asymmetric walls reveal an evolution of the domain wall tilting angle with ring thickness which can be understood from the thickness dependencies of the contributing energy terms. Analysis of all the data reveals that in addition to the geometry, the influence of materials properties, defects and thermal activation all need to be taken into account in order to understand and reliably control the experimentally accessible states, as needed for devices.2

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“…This reflects the directionality of the exchange interactions in FePt. The directionality of the DW width and energy is an important factor which will effect other experimental properties, such as the domain wall mobility [9][10][11], magneto-resistance [12], switching fields and switching modes. Furthermore, it should be considered in micromagnetic calculations on FePt (and other layered magnets).…”

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Orientation and temperature dependence of domain wall properties in FePt

Hinzke

Nowak

Chantrell

et al. 2007

Applied Physics Letters

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An investigation of the orientation and temperature dependence of domain wall properties in FePt is presented. The authors use a microscopic, atomic model for the magnetic interactions within an effective, classical spin Hamiltonian constructed on the basis of spin-density functional calculations. They find a significant dependence of the domain wall width as well as the domain wall energy on the orientation of the wall with respect to the crystal lattice. Investigating the temperature dependence, they demonstrate the existence of elliptical domain walls in FePt at room temperature. The consequences of their findings for a micromagnetic continuum theory are discussed. (c) 2007 American Institute of Physics

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Domain wall mobility in nanowires: Transverse versus vortex walls

Cited by 122 publications

References 8 publications

Reversal modes in magnetic nanotubes

Reversal modes in magnetic nanotubes

Domain wall spin structures in mesoscopic Fe rings probed by high resolution SEMPA

Orientation and temperature dependence of domain wall properties in FePt

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