Transition between Bloch and Néel Walls

Torok, E. J.; Olson, A. L.; Oredson, H. N.

doi:10.1063/1.1714317

Cited by 38 publications

(15 citation statements)

References 5 publications

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“…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. However, he conjectured that wall types with 2D spin arrangements with lower energy might exist, explaining, for instance, the occurrence of cross-tie walls [2].…”

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confidence: 99%

“…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.…”

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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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Achiral tilted domain walls in perpendicularly magnetized nanowires

et al. 2017

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“…This conclusion contradicts observations made by Lorentz electron microscopy though they confirmed a general sequence of DWs transformations. 14 We modernize Néel-Middelhoek model suggesting that a stray field in DW H s n ð Þ ¼ À4pNM n ð Þ follows a spatial distribution of the magnetization. This assumption, known as a Winter approximation, 15 wholly corresponds to the finite element analysis of magnetostatic problem when arbitrarily shaped inhomogeneously magnetized sample is considered as a layered stack of uniformly magnetized thin sheets.…”

Section: Domain Structurementioning

confidence: 99%

“…With a further field decrease this angle gradually grows reaching 90 at H ¼ 0. Crossing zero field, Bloch DW remains energetically favorable until a nucleation of Néel DW with the magnetization 9) and (14). Pure Bloch DW parallel to the "easy"-axis could exist in the entire range of magnetic fields ÀH p < H < H p .…”

Section: Domain Wall Transformationsmentioning

confidence: 99%

Ferromagnetic resonance, magnetic susceptibility, and transformation of domain structure in CoFeB film with growth induced anisotropy

Manuilov

Grishin

Munakata

2011

Journal of Applied Physics

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Field dependence of magnetic susceptibility in nanocrystalline CoFeB film was studied in a wide frequency range from 500 kHz to 15 GHz. Anomalies of the susceptibility were detected exciting CoFeB film with a solenoidal coil, microwave strip line, in the tunable microwave cavity as well as employing magneto-optical domains imaging. Critical spin fluctuations in the form of "soft" modes were observed in a whole range of orientations of magnetic field perpendicular to the "easy" magnetic axis. A sequence of domain structure transformations was extensively examined in a "hard" direction in in-plane magnetic field reduced below the field of uniaxial anisotropy H p ¼ 535 Oe. At first, uniformly magnetized state in CoFeB film transforms to stripe domains separated by low angle Néel domain walls (DWs) parallel to the "hard"-axis. Then, at critical field H cr ¼ 232 Oe, Néel DWs gradually convert to the"easy"-axis oriented Bloch DWs loaded with vertical Bloch lines (VBLs). After field reversal at H ¼ ÀH cr , backward conversion of VBL-loaded Bloch DWs to Néel DWs results in instantaneous energy release and sharp anomaly of magnetic susceptibility. Appearance of critical spin fluctuations accomplishes domains transformation to the uniformly magnetized state at H ¼ À535 Oe.

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“…Indeed, by incorporating these parameters into (1) we obtained f A = 1.805 GHz, a value close to the experimental f A = 2.199 GHz. However, at t > 100 nm, the f A decreased slightly for all s. This may be a result of nonuniform magnetization in a thick ferromagnetic film [19,[46][47][48]. Chen et al [46] suggested that the uniform mode (k = 0) of spin waves may be scattered into magnons (k ࣔ 0) by this locally nonuniform magnetization and cause the resonance frequency to shift.…”

Section: The Effect Of Thicknessmentioning

confidence: 99%

Comparative study of the ferromagnetic resonance behavior of coupled rectangular and circular Ni80Fe20rings

2014

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A systematic investigation of the dynamic behavior of Ni 80 Fe 20 ring arrays using broadband ferromagnetic resonance spectroscopy as a function of inter-ring spacing and ring thickness is presented. Four distinct resonance modes were found for rectangular rings compared to the two modes seen in circular rings of identical width due to the presence of sharp corners and nonuniform demagnetization field distribution. The resonance peaks were sensitive to the inter-ring spacing and the ring thickness due to magnetostatic coupling. Micromagnetic simulations and analytical calculations are compared with the experiment results.

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Transition between Bloch and Néel Walls

Cited by 38 publications

References 5 publications

Achiral tilted domain walls in perpendicularly magnetized nanowires

Achiral tilted domain walls in perpendicularly magnetized nanowires

Ferromagnetic resonance, magnetic susceptibility, and transformation of domain structure in CoFeB film with growth induced anisotropy

Comparative study of the ferromagnetic resonance behavior of coupled rectangular and circular Ni80Fe20rings

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