Analytic theory for the switch from Bloch to Néel domain wall in nanowires with perpendicular anisotropy

DeJong, M. D.; Livesey, Karen L.

doi:10.1103/physrevb.92.214420

Cited by 35 publications

(30 citation statements)

References 21 publications

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“…By introducing DMI, Néel walls are stabilized, shifting the start of the transition to 68 nm and preventing pure Bloch walls even in 500-nm-wide wires. Our measured domain walls from Table I thickness [5,15], contrary to our experimental findings. The possible existence of a "mixed wall" was discussed by Aharoni [16] in the context of in-plane magnetized films and discarded for the 1D case by a rigorous energy minimization of all possible configurations.…”

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confidence: 99%

“…The Bloch wall is the energetically preferred state in perpendicularly magnetized films irrespective of film thickness. Néel walls can be made the ground state by changing the geometry to wires [4,5] or adding constrictions [6], by applying magnetic fields [7,8], or by introducing Dzyaloshinskii-Moriya exchange interaction (DMI) [9].The Bloch-Néel wall transition in perpendicularly magnetized nanowires, as a function of the wire width, was indirectly observed by measuring a change in the anisotropic magnetoresistance (AMR) [10]. Most recently, it was studied analytically [5].…”

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confidence: 99%

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confidence: 99%

“…Most recently, it was studied analytically [5]. A direct observation of this transition in real space is missing.…”

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confidence: 99%

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Achiral tilted domain walls in perpendicularly magnetized nanowires

et al. 2017

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Perpendicularly magnetized nanowires exhibit distinct domain wall types depending on the geometry. Wide wires contain Bloch walls, narrow wires Néel walls. Here, the transition region is investigated by direct imaging of the wall structure using high-resolution spin-polarized scanning electron microscopy. An achiral intermediate wall type is discovered that is unpredicted by established theoretical models. With the help of micromagnetic simulations, the formation of this novel wall type is explained.In recent years, domain walls in perpendicularly magnetized materials have been intensely investigated because they are narrower than in in-plane systems and therefore, when used to store a data bit, promise higher storage density. In perpendicularly magnetized systems, domain walls are of Bloch type, i.e., the magnetization rotates within the wall plane. In in-plane magnetized systems, in contrast, diverse wall types exist. In bulk, again Bloch walls prevail, whereas in thin films, the energetically favored wall type is a Néel wall, i.e., the magnetization rotates perpendicularly to the plane of the wall. In between, a finite film-thickness range exists in which domain walls are neither of Bloch nor of Néel type. They are characterized by more complex arrangements of spins, such as zigzag patterns [1], cross-ties [2] or continuous asymmetric deformations [3]. The Bloch wall is the energetically preferred state in perpendicularly magnetized films irrespective of film thickness. Néel walls can be made the ground state by changing the geometry to wires [4,5] or adding constrictions [6], by applying magnetic fields [7,8], or by introducing Dzyaloshinskii-Moriya exchange interaction (DMI) [9].The Bloch-Néel wall transition in perpendicularly magnetized nanowires, as a function of the wire width, was indirectly observed by measuring a change in the anisotropic magnetoresistance (AMR) [10]. Most recently, it was studied analytically [5]. A direct observation of this transition in real space is missing. Both Bloch and Néel walls were observed in thin films by spinpolarized scanning tunneling microscopy [11], in multilayers by spin-polarized low-energy electron microscopy [12], and in nanowires by optically monitoring the Zeeman shift of the electron spin in a nitrogen-vacancy defect in diamond [13].In this work, we investigate domain walls at the BlochNéel wall transition in flat nanowires (or "nanostrips") with perpendicular magnetic anisotropy as a function of the nanowire width. We image the wall structure in real space using high-resolution spin-polarized scanning electron microscopy (spin-SEM), which is capable of determining the specimen's magnetization by measuring the

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confidence: 99%

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confidence: 99%

“…Most recently, it was studied analytically [5]. A direct observation of this transition in real space is missing.…”

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confidence: 99%

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Achiral tilted domain walls in perpendicularly magnetized nanowires

et al. 2017

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“…In the calculation of the DW length, the following magnetization profile for the Néel wall was assumed [34],…”

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confidence: 99%

Efficient in-line skyrmion injection method for synthetic antiferromagnetic systems

2018

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Although it has been proposed that antiferromagnetically-coupled skyrmions can be driven at extremely high speeds, such skyrmions are near impossible to inject with current methods. In this paper, we propose the use of DMI-induced edge magnetization tilting to perform in-line skyrmion injection in a synthetic antiferromagnetic branched nanostructure. The proposed method circumvents the skyrmion topological protection and lowers the required current density. By allowing additional domain walls (DWs) to form on the branch, the threshold injection current density was further reduced by 59%. The increased efficiency was attributed to inter-DW repulsion and DW compression. The former acts as a multiplier to the effective field experienced by the pinned DW while the latter allows DWs to accumulate enough energy for depinning. The branch geometry also enables skyrmions to be shifted and deleted with the use of only three terminals, thus acting as a highly scalable skyrmion memory block.

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Magnetization Configurations and Reversal in Small Magnetic Elements

Reeve

Vafaee

Kläui

2019

Materials Science and Technology

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In this article, we present an overview of various static magnetization configurations and their dynamic reversal modes for elements of typical sizes from a few nanometers to a few micrometers. Initially, commonly employed techniques for the magnetic imaging and characterization of such systems are briefly reviewed. We then concisely outline the basic theoretical details of micromagnetism and in particular the main energy terms that determine the formation and dynamics of different states. To describe the simplest case of a single‐domain system, we present Stoner–Wohlfarth theory and compare its predictions to experimental studies. For larger elements, we discuss the formation of nonuniform and multidomain states, based on a fine balance of the aforementioned energy terms. In particular, for the most widely studied high‐symmetry geometries, the interplay between these energy terms and the element shape for the formation of the prevalent states is discussed. Next, the dynamic reversal of the elements is presented, beginning with the Landau–Lifshitz–Gilbert equation that governs uniform dynamics of single‐domain systems. Further reversal modes including curling, buckling, and domain wall motion are presented for nonuniform states, by a number of case studies. The work is primarily motivated from a fundamental standpoint, but links to potential device applications are highlighted throughout.

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Analytic theory for the switch from Bloch to Néel domain wall in nanowires with perpendicular anisotropy

Cited by 35 publications

References 21 publications

Achiral tilted domain walls in perpendicularly magnetized nanowires

Achiral tilted domain walls in perpendicularly magnetized nanowires

Efficient in-line skyrmion injection method for synthetic antiferromagnetic systems

Magnetization Configurations and Reversal in Small Magnetic Elements

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