Switching processes and switching reproducibility in ferromagnetic ring structures

Kläui, Mathias; Vaz, C. A. F.; Bland, J. A. C.; Sinnecker, E. H. C. P.; Guimarães, A.P.; Wernsdorfer, Wolfgang; Faini, G.; Cambril, E.; Heyderman, Laura J.; Dávid, Christian

doi:10.1063/1.1640451

Cited by 53 publications

(33 citation statements)

References 11 publications

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“…As the angle is increased ͑decreased͒ further, we find that the depinning field increases again until at above 210°͑below −30°͒ the reversal does not take place by the depinning of the pinned domain wall, but rather by the nucleation of a new reverse domain at the applied field angle and subsequent domain wall propagation that annihilates the wall located at the constriction. 9 Such a nucleation occurs at about 650 Oe, 9 and is also confirmed by measurements between different contacts for this sample.…”

Section: F509-2 09f509mentioning

confidence: 60%

“…3,7 Such pinning centers provide welldefined stable locations for domain walls. Pinning centers can result from imperfections in the material, 8,9 in order to reliably engineer pinning, artificially structured variations in the geometry of an element have been introduced. While protrusions in wires have been used, 10,11 constrictions have been shown to yield particularly well-defined pinning centers.…”

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confidence: 99%

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Angular dependence of the depinning field for head-to-head domain walls at constrictions

Bedau

Kläui

Rüdiger

et al. 2007

Journal of Applied Physics

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The angular dependence of the depinning field of vortex and transverse domain walls is determined experimentally for NiFe rings with nanometer size constrictions. From the angular dependence, we are able to deduce the potential landscape caused by the constriction and seen by the wall. The potential minimum for transverse walls is at the notch position so that these walls are pinned symmetrically inside the constriction. Vortex walls are pinned at a position adjacent to the constriction and this position can be determined from the angular variation of the depinning fields. Good agreement with the results of micromagnetic simulations is obtained.Recently interest in magnetic domain walls has been surging, fueled by fundamental interest in the magnetic properties, the spin structure and pinning characteristics. Furthermore, devices with switching by field-induced 1 as well as current-induced 1 domain wall motions 2,3 have been suggested.To control the domain wall behavior and, in particular, the switching, pinning centers can be used to confine the wall propagation in field-induced switching 4-6 and also in currentinduced switching.3,7 Such pinning centers provide welldefined stable locations for domain walls. Pinning centers can result from imperfections in the material, 8,9 in order to reliably engineer pinning, artificially structured variations in the geometry of an element have been introduced. While protrusions in wires have been used, 10,11 constrictions have been shown to yield particularly well-defined pinning centers. 5,7,[12][13][14][15] In addition to applications, such as domain wall diodes in logic devices, 11 constrictions have also allowed the determination of more fundamental properties of domain walls, such as magnetoresistance ͑MR͒ effects associated with domain walls. 13Domain walls move in an effective potential landscape generated by geometrical variations.12-14 Rings have proven to be an apt geometry since domain walls can be positioned easily using uniform fields applied along appropriate directions. 16 In an earlier work, we observed that constrictions create an attractive potential well for transverse walls which are pinned in the constriction ͓see Fig. 1͑c͔͒. While vortex walls are repelled from a constriction and pinned adjacent to it ͓see Fig. 1͑c͔͒. The width and depth of the attractive potential well generated by a constriction have been measured along one direction in Refs. 12 and 13. In particular, for vortex walls the field was always applied in a direction to pull the wall away from the constriction, while the field to pull a domain wall across and through a constriction has not been determined. In order to determine the full potential landscape, the depinning field has to be measured for all angles.In this paper we probe the angular variation of the pinning potential of domain walls at a constriction. The experimentally obtained results are compared with micromagnetic simulations.The ring structures for this work were fabricated in a two-step lift-off process. The magnetic rings...

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Section: F509-2 09f509mentioning

confidence: 60%

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confidence: 99%

Angular dependence of the depinning field for head-to-head domain walls at constrictions

Bedau

Kläui

Rüdiger

et al. 2007

Journal of Applied Physics

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“…Such asymmetries are always present in these samples due to geometrical irregularities, etc. [31]. For current densities above 0:2 10 12 A=m 2 , no significant change of the critical field can be observed up to the critical current density.…”

Section: -2mentioning

confidence: 95%

Temperature Dependence of the Spin Torque Effect in Current-Induced Domain Wall Motion

et al. 2006

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We present an experimental study of domain wall motion induced by current pulses as well as by conventional magnetic fields at temperatures between 2 and 300 K in a 110 nm wide and 34 nm thick Ni 80 Fe 20 ring. We observe that, in contrast with field-induced domain wall motion, which is a thermally activated process, the critical current density for current-induced domain wall motion increases with increasing temperature, which implies a reduction of the spin torque efficiency. The effect of Joule heating due to the current pulses is measured and taken into account to obtain critical fields and current densities at constant sample temperatures. This allows for a comparison of our results with theory. PACS numbers: 72.25.Ba, 75.60.Ch, 75.75.+a, 85.70.Kh The interplay between spin currents and domain walls in magnetic nanostructures has been studied intensively in the last decade, driven by fundamental interest in the basic physical mechanisms involved. Furthermore, currentinduced magnetization reversal by domain wall motion is a promising alternative to the conventional field-induced reversal for technological applications in nonvolatile memories and sensors, which has lead to an increase in research in this field [1]. The phenomenon of current-induced domain wall motion has been long known [2,3] and recently controlled current-induced motion of single domain walls in magnetic nanostructures has been achieved. Several important aspects such as domain wall velocities [4,5], critical current densities [6 -8], thermally assisted motion [9], and the deformation of the domain wall spin structure due to current [4] have been addressed. Current-induced switching has been also investigated in a trilayer pillar geometry at variable temperatures [10,11]. The underlying theory of interaction between current and magnetization is still controversial. Different approaches have been suggested in the ballistic limit [12,13] as well as in the diffusive limit [2,12]. An adiabatic spin torque has been introduced into the Landau-Lifshitz-Gilbert equation of magnetization dynamics [12,14,15]. Motivated by large discrepancies between experiment and theory, a nonadiabatic term was included [16,17]. The relative importance of the two torques in domain wall motion is still the subject of much debate [16 -18]. In order to gain information on the (non)-adiabaticity of the spin torque, a study of domain wall motion as a function of current and field at a constant sample temperature is needed. Using combinations of current and field allows one to compare the theoretical calculations [18] of the dependence of the critical current on the applied field with the experimental results. Of particular importance for comparison of experiment and theory is a constant sample temperature to separate spin torque and temperature effects, because existing theory so far neglects heating effects. Since significant Joule heating due to injected current pulses was observed [19], this effect must be quantitatively measured and taken into account. The possibi...

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“…Very few studies of angular dependence in the magnetic rings have been reported that too only for in-plane field rotation. 20,21 A decrease of H C1 with angle and a symmetrical minimum at 45 was reported for ring arrays. 20 Large and no variation in the values of H C1 and H C2 as a function of angle, respectively, was reported for single ring.…”

Section: Resultsmentioning

confidence: 99%

Magnetization reversal and dynamics in non-interacting NiFe mesoscopic ring arrays

Kaur

Husale

Varandani

et al. 2014

Journal of Applied Physics

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The dynamics of magnetization (M) reversal and relaxation as a function of temperature (T) are reported in three non-interacting NiFe ring arrays having fixed ring outer diameter and varying widths. Additionally, the dependence of M(H) loop on the angle (h) between magnetic field (H) and the plane of the rings is addressed. The M(H) loops show a double step transition from onion state (OS) to vortex state (VS) at all temperatures (T ¼ 3 to 300 K) and angles (h ¼ 0 to 90 ). The critical reversal fields H C1 (OS to VS) and H C2 (VS to OS) show a pronounced dependence on T, ring width, and h. Estimation of the transverse and vortex domain wall energies reveals that the latter is favored in the OS. The OS is also the remanent state in the smallest rings and decays with the effective energy scale (U 0 /T) of 50 and 32 meV/K at 10 and 300 K, respectively. The robust in-plane anisotropy of magnetization of ring assemblies is established by scaling the M(H) with h.

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Switching processes and switching reproducibility in ferromagnetic ring structures

Cited by 53 publications

References 11 publications

Angular dependence of the depinning field for head-to-head domain walls at constrictions

Angular dependence of the depinning field for head-to-head domain walls at constrictions

Temperature Dependence of the Spin Torque Effect in Current-Induced Domain Wall Motion

Magnetization reversal and dynamics in non-interacting NiFe mesoscopic ring arrays

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