Magnetic reversal of cylindrical nickel nanowires with modulated diameters

Pitzschel, Kristina; Bachmann, Julien; Martens, Stephan; Montero-Moreno, Josep M.; Kimling, Judith; Meier, Guido; Escrig, Juan; Nielsch, Kornelius; Görlitz, Detlef

doi:10.1063/1.3544036

Cited by 69 publications

(70 citation statements)

References 47 publications

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“…To stabilize domain walls in nanowires we make use of local protrusions placed every other several micrometers, to act as potential barriers for domain walls motion. While these barriers are not sufficient to pin domain walls when the magnetic field is applied along the wire [24], we found that they are fit to prevent motion of domain walls upon dc oscillatory demagnetization with the magnetic field applied perpendicular to the wafer plane.…”

mentioning

confidence: 84%

Observation of Bloch-point domain walls in cylindrical magnetic nanowires

Col

Jamet²,

Rougemaille³

et al. 2014

Phys. Rev. B

168

151

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Topological protection is an elegant way of warranting the integrity of quantum and nanosized systems. In magnetism one example is the Bloch-point, a peculiar object implying the local vanishing of magnetization within a ferromagnet. Its existence had been postulated and described theoretically since several decades, however it has never been observed. We confirm experimentally the existence of Bloch points, imaged within domain walls in cylindrical magnetic nanowires, combining surface and transmission XMCD-PEEM magnetic microscopy. This opens the way to the experimental search for peculiar phenomena predicted during the motion of Bloch-point-based domain walls.There is a rising interest for physical systems providing topological protection. The interest is both fundamental to elucidate the underlying physical phenomena, and applied as a mean to provide robustness to a state against external perturbations and decoherence pathways. For example, the peculiar topology of the band structure of carbon nanotubes and graphene forbids backscattering of charge carriers [1], an effect which is often invoked to explain the high mobilities up to room temperature [2]. A similar effect occurs at the surface of so-called topological insulators, together with a locking of the spin of charge carriers; this provides spin currents protected against depolarization [3]. A photonic analogue was also designed by combining helical wave guides on a lattice with a graphene-like honeycomb topology, removing time-reversal symmetry and thereby preventing backscattering of light [4].In systems displaying a directional order parameter such as liquid crystals and ferromagnets, interesting phenomena are associated with the slowly-varying texture of the order field (magnetization for a ferromagnet). The requirement of local continuity of a vector field with fixed magnitude provides a topological protection against the transformation of the texture. A prototypical case in magnetism is skyrmions, which are essentially local two-dimensional chiral spin textures stabilized by the Dzyaloshinskii-Moriya interaction, embedded in an otherwise uniformly-magnetized surrounding. Despite these surroundings skyrmions cannot unwind continuously as explained by the above continuity constraints of the magnetization field, explaining their topological protection. Skyrmions have first been predicted theoretically [5], then confirmed experimentally in both bulk [6] and thin film forms [7].Bloch points are yet another type of topologicallyprotected magnetic texture which cannot be unwound, however of a three-dimensional nature. Bloch points are such that given the distribution of magnetization set on a closed surface like a sphere, the enclosed volume cannot be mapped with a continuous magnetization field of finite magnitude. This occurs e.g. for hedge-hog configurations, or more generally whenever all directions of magnetization are mapped on the closed surface (Fig. 1a-b). Such boundary conditions imply the local cancellation of the modulus of magnetization on a...

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mentioning

confidence: 84%

Observation of Bloch-point domain walls in cylindrical magnetic nanowires

Col

Jamet²,

Rougemaille³

et al. 2014

Phys. Rev. B

168

151

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“…Recent progress in sample growth has allowed to create free-standing nanowires which are grown perpendicular to their substrate (for example [44][45][46]. While it is outside the scope of this work to investigate these systems in detail, we comment briefly on possible analytical approximations.…”

Section: Perpendicular Nanowiresmentioning

confidence: 99%

Joule heating in nanowires

et al. 2011

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We study the effect of Joule heating from electric currents flowing through ferromagnetic nanowires on the temperature of the nanowires and on the temperature of the substrate on which the nanowires are grown. The spatial current density distribution, the associated heat generation, and diffusion of heat is simulated within the nanowire and the substrate. We study several different nanowire and constriction geometries as well as different substrates: (thin) silicon nitride membranes, (thick) silicon wafers, and (thick) diamond wafers. The spatially resolved increase in temperature as a function of time is computed.For effectively three-dimensional substrates (where the substrate thickness greatly exceeds the nanowire length), we identify three different regimes of heat propagation through the substrate: regime (i), where the nanowire temperature increases approximately logarithmically as a function of time. In this regime, the nanowire temperature is well-described analytically by You et al.[ APL89, 222513 (2006)]. We provide an analytical expression for the time tc that marks the upper applicability limit of the You model. After tc, the heat flow enters regime (ii), where the nanowire temperature stays constant while a hemispherical heat front carries the heat away from the wire and into the substrate. As the heat front reaches the boundary of the substrate, regime (iii) is entered where the nanowire and substrate temperature start to increase rapidly.For effectively two-dimensional substrates (where the nanowire length greatly exceeds the substrate thickness), there is only one regime in which the temperature increases logarithmically with time for large times, before the heat front reaches the substrate boundary. We provide an analytical expression, valid for all pulse durations, that allows one to accurately compute this temperature increase in the nanowire on thin substrates.

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“…1(c,e). As already noticed, modulations of diameter 16 as well as roughness or structural / anisotropy fluctuations 20 also induce a local contrast, with monopolar and dipolar feature along the wire direction, respectively. However, a closer look reveals also a transverse dark/light dipolar contrast perpendicular to the axis at DWs, diameter modulations and wire ends (Fig.…”

Section: Imagingmentioning

confidence: 81%

“…1(a-c), and was used by us to evidence again transverse walls and also for the first time Bloch-point walls by photo-emission electron microscopy 17 . Note however that, as the resulting pinning field is expected to be lower than the longitudinal nucleation field H n , a magnetization process with a magnetic field applied along the wire axis still consists of nucleation-propagation-annihilation and cannot lead to a multi-domain wire 16 . The second procedure consists in making use of a curved shape, saturating magnetization across the radius, before coming back to remanence.…”

Section: Nucleationmentioning

confidence: 99%