Structure of cross-tie wall in thin Co films resolved by magnetic force microscopy

Löhndorf, M.; Wadas, A.; Berg, Holger; Wiesendanger, R.

doi:10.1063/1.115754

Cited by 47 publications

(39 citation statements)

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“…As the ferromagnet thickness decreases, demagnetizing fields increase, which means that it becomes increasingly energetically favorable for domain walls to mutate from the out-of-plane to in-plane direction. This has been demonstrated in experiments in Co, Permalloy (Py), and Ni samples, [19][20][21][22] where it has been observed that the transition between these two types of domain walls occurs at around 30 nm for Co and 20 nm for Ni.…”

Section: Introductionmentioning

confidence: 80%

Vortex flipping in superconductor/ferromagnet spin-valve structures

et al. 2013

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We report in-plane magnetization measurements on Ni/Nb/Ni/CoO and Co/Nb/Co/CoO spin valve structures with one of the ferromagnetic layers pinned by an antiferromagnetic layer. In samples with Ni below the superconducting transition T c , our results show strong evidence of vortex flipping driven by ferromagnet magnetization. This is a direct consequence of the proximity effect that leads to vortex supercurrent leakage into the ferromagnets. Here, the polarized electron spins are subject to the vortices' magnetic field, occasioning vortex flipping. Such a novel mechanism has been made possible by fabrication of the ferromagnet/superconductor/ferromagnet/antiferromagnet multilayered spin valves with an S layer thin enough to barely confine vortices inside as well as F layers thin enough to align and control magnetization within the plane. When Co is used, the vortex flipping effect is not observed. This is attributed to the shorter coherence length of Co. Interestingly, a reduction in the pinning field of about 400 Oe is observed instead when the Nb layer is in the superconducting state. This effect cannot be explained in terms of vortex fields. In view of these facts, any explanation must be directly related to the proximity effect and thus a remarkable phenomenon that deserves further investigation.

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Section: Introductionmentioning

confidence: 80%

Vortex flipping in superconductor/ferromagnet spin-valve structures

et al. 2013

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“…Many of the results on the theory of the domain walls can be found in books [1,2]. In particular, there are analytical expressions for the distribution of the magnetization vector inside of the one-dimensional Bloch and Néel domain walls, which are the starting point for calculating their static and dynamic properties.The cross-tie domain wall was also observed in a number of experiments a that time (see Ref.3 and references therein) and also with modern high resolution techniques [4,5,6], and are usual in thin and ultra-thin magnetic films important for modern applications [7]. However, there is no [4] (also see p. 163 in Ref.…”

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confidence: 99%

“…3 and references therein) and also with modern high resolution techniques [4,5,6], and are usual in thin and ultra-thin magnetic films important for modern applications [7]. However, there is no [4] (also see p. 163 in Ref.…”

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confidence: 99%

Simple analytical description for the cross-tie domain wall structure

Metlov

2001

Applied Physics Letters

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A closed form analytical expression for the magnetization vector distribution within the cross-tie domain wall in an isotropic ferromagnetic thin film is given. The expression minimizes the exchange energy functional exactly, and the magnetostatic energy by means of an adjustable parameter (wall width). The equilibrium value of the wall width and the film thickness corresponding to the transition between the Néel and the cross-tie walls are calculated. The results are compared with the recent experiments and are in good qualitative agreement.The structure of magnetic domain walls (transition regions separating magnetic domains) was in a focus of extensive research in 1930s -60s and during the time a lot of useful results on the static structures of various wall types as well as their dynamic properties were obtained. Many of the results on the theory of the domain walls can be found in books [1,2]. In particular, there are analytical expressions for the distribution of the magnetization vector inside of the one-dimensional Bloch and Néel domain walls, which are the starting point for calculating their static and dynamic properties.The cross-tie domain wall was also observed in a number of experiments a that time (see Ref.3 and references therein) and also with modern high resolution techniques [4,5,6], and are usual in thin and ultra-thin magnetic films important for modern applications [7]. However, there is no [4] (also see p. 163 in Ref.2) closed form analytical expression for the cross-tie wall structure. This is, probably, due to the fact that magnetization distribution even in straight cross-tie domain wall is two-dimensional (unlike one-dimensional ones of Bloch and Néel walls). It means, the structure of such a wall is defined by a system of non-linear integral (due to the long-range dipolar interactions) partial differential equations, and there is no way to reduce this system to a single equation (as it was done for the Néel wall [8]).Consider a thin film having the thickness h made of soft (isotropic) magnetic material, in the Cartesian coordinate system X, Y , Z chosen in such a way that 0Z axis is perpendicular to the film plane. The parameters of the material entering the calculation are the exchange constant C, and the saturation magnetization constant M S . If the film is thin enough, so that h is of the order of a few exchange lengths L E = C/M 2 S , the dependence of the magnetization distribution on Z can be neglected and the task becomes essentially two-dimensional. If we also neglect the dipolar interaction for a while, the magnetization distribution M ( r) = M S m( r), | m| = 1, r = {X, Y } is defined by the minimum of the exchange energy functional:where the integration runs over all X − Y plane. The last expression is given using the parametrization of the magnetization vector field by a complex function w(z, z) of a complex variable z = X+ıY , ı = √ −1, line over a variable means complex conjugation, so that m x +ım y = 2w/(1+ww) and m z = (1−ww)/(1+ww), ∂/∂z = (∂/∂X −ı∂/∂X)/2, ∂/∂z = (∂...

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“…7a (running from its top to bottom) is characterized by the presence of four segments: dark and bright ones on each side of the domain wall (with reversed contrast with respect to the wall, see encircled areas in the image). Such a MFM image is typical for cross-tie wall [42]. In regions such as that shown in Fig.…”

Section: Resultsmentioning

confidence: 97%

“…5a-f). The ripple structure is directly related to the polycrystalline character of the studied films and is due to local variations of the magnetic anisotropy [39,42]. The ripple direction is always oriented perpendicular to the magnetization direction and hence the magnetic easy axis [39,42].…”

Section: Resultsmentioning

confidence: 99%

Investigation of thermally evaporated nanocrystalline thin cobalt films

et al. 2017

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structures are of large importance. From the practical point of view, they are very significant for tailoring of the specimens with the required properties. In particular, they allow to develop high-density magnetic and magneto-optic recording media, modern recording heads, high-performance permanent magnets, magnetic sensors, and transformer steel sheets [1,2]. The knowledge of the magnetic domain behavior in relation to the morphological structure of the specimens is also important for theoretical modeling of magnetic properties [1,2].Thin magnetic films attract large attention from the fundamental as well as technological point of view. On the fundamental side, they exhibit different magnetic properties, such as magnetic anisotropy [3], magnetic microstructure [4], coercivity [5], and magnetoresistance [6], depending on their thickness, composition, crystalline structure, and preparation conditions. From the technological point of view, thin magnetic films have a number of applications; for example, they are used in magnetic information storage media, magneto-optic recording media, magnetic devices, and sensors [1,2].In particular, cobalt thin films have been the subject of wide and intense study in recent years. They can be prepared by various techniques, for example by sputtering, thermal evaporation, electron beam evaporation, molecular beam epitaxy, pulsed laser deposition, electrodeposition, and chemical vapor deposition [7][8][9]. The obtained films are usually nanocrystalline in nature and possess specific, improved mechanical, physical, magnetic, and chemical properties in comparison with conventional microcrystalline counterparts. Depending on the film thickness as well as the preparation method and conditions used, cobalt thin films exhibit a wide range of morphological and magnetic properties, and especially various magnetic domain structures with inplane and outofplane magnetization [10][11][12][13]. AbstractIn this paper, a study has been made of nanocrystalline thin cobalt films with thicknesses in the range from 10 to 60 nm. The films were thermally evaporated at incidence angle of 0° in a vacuum of about 10 − 5 mbar. The morphological structure of the films consists of nanocrystalline grains regular in shape and densely packed. As the film thickness is increased from 10 to 60 nm, the average grain size increases from 22.0 to 28.9 nm. The films crystallize mainly in the hexagonal close-packed phase of cobalt. The magnetic structure is composed of domains. In films with thicknesses in the range from 10 to 40 nm, the domains are magnetized in the plane of the film, while films with thicknesses of 50 and 60 nm possess both inplane and perpendicular magnetization components. The domains with inplane magnetization are irregular in shape and typically from a few to 10 mm in size, whereas the domains with perpendicular magnetization form a fine maze stripe pattern of the order of 100 nm in width.

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Structure of cross-tie wall in thin Co films resolved by magnetic force microscopy

Cited by 47 publications

References 0 publications

Vortex flipping in superconductor/ferromagnet spin-valve structures

Vortex flipping in superconductor/ferromagnet spin-valve structures

Simple analytical description for the cross-tie domain wall structure

Investigation of thermally evaporated nanocrystalline thin cobalt films

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