Magnetic force microscopy studies of domain walls in nickel and cobalt films

Hsieh, Cheng‐Ting; Liu, J.Q.; Lue, Juh Tzeng

doi:10.1016/j.apsusc.2005.05.041

Cited by 58 publications

(31 citation statements)

References 17 publications

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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: 79%

“…The Ni thickness d Ni = 3 nm is approximately twice the ferromagnetic coherence length ξ Ni ∼ 1.2 nm in the dirty limit, 25 so we expect Cooper pairs to penetrate to almost half the entire Ni thickness. Also, the small thickness of the ferromagnet implies that domain walls lie in-plane, 20 eliminating stray field effects from domain wall formation.…”

Section: A Nb/co Bilayersmentioning

confidence: 99%

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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: 79%

Section: A Nb/co Bilayersmentioning

confidence: 99%

Vortex flipping in superconductor/ferromagnet spin-valve structures

et al. 2013

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“…[12], it occurs in films thicker than 5 nm. Absence of a domain structure is important for obtaining reproducible I c (H) characteristics.…”

Section: Device Characterizationmentioning

confidence: 97%

Critical Current Gain in High-jc Superconducting-Ferromagnetic Transistors

Nevirkovets

Shafraniuk

Chernyashevskyy

et al. 2016

IEEE Trans. Appl. Supercond.

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We report experimental and theoretical results on the current gain in superconductor-ferromagnetic transistors (SFTs) with the SISFIFS structure (where S, I, and F denote a superconductor (Nb), an insulator (AlO x ), and a ferromagnetic material (Ni), respectively). The Josephson critical current density, j ca , of the acceptor (SISF) junction in the devices is above 9 kA/cm 2 , which is higher than that in our previous devices. The critical current gain is defined as |δ δ δ δI ca |/|δ δ δ δI i |, where a change |δ δ δ δI i | in the injector (SFIFS junction) current produces a change |δ δ δ δI ca | in the acceptor maximum Josephson current. We observed a smallsignal gain as high as 7.8 and a large-signal current gain of about 2.2. In addition, we found that the Josephson current of the acceptor junction is sensitive to the state of the ferromagnetic layers. A theoretical model is proposed to describe the nonequilibrium processes in the SFT devices, which agrees with the experimental observations. The calculation shows that, in the present device configuration, the dominant contribution to the gap suppression in the middle Nb electrode is due to the quasiparticle injection; spin injection plays a secondary role. We demonstrate that proper device engineering allows one to efficiently control the maximum Josephson current in the SISF acceptor junction using the quasiparticle injection. We conclude that SFT devices can be used as input/output isolators and amplifiers for memory, digital, and RF applications. IndexTerms-Ferromagnetic-superconducting hybrid structures, quasiparticle injection, Josephson effect, proximity effect, superconductivity, superconducting transistor

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“…For a vortex pinned on a Bloch wall of width  (~50nm [16]) in a Ni film of thickness d the interaction is approximately given by…”

Section: Discussionmentioning

confidence: 99%

Continuously tuneable critical current in superconductor-ferromagnet multilayers

Curran

Kim

Satchell

et al. 2017

Applied Physics Letters

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We demonstrate that the critical current of superconducting Nb/Ni multilayers can be continuously tuned by up to a factor of three during magnetization reversal of the Ni films under an applied in-plane magnetic field. Our observations are in reasonably good agreement with a model of vortex pinning by Bloch domain walls that proliferate in the samples during magnetization reversal, whereby each vortex interacts with at most one wall in any of the Ni layers. Our model suggests ways in which the controllable pinning effect could be significantly enhanced, with important potential applications in tuneable superconducting devices.

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Magnetic force microscopy studies of domain walls in nickel and cobalt films

Cited by 58 publications

References 17 publications

Vortex flipping in superconductor/ferromagnet spin-valve structures

Vortex flipping in superconductor/ferromagnet spin-valve structures

Critical Current Gain in High-jc Superconducting-Ferromagnetic Transistors

Continuously tuneable critical current in superconductor-ferromagnet multilayers

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