Fabrication and magnetic properties of prepatterned epitaxial nanodots

Kläui, Mathias; Lewis, Paul A.; Vaz, C. A. F.; Bleloch, Andrew; Speaks, R.; Blamire, M.C.; Bland, J. A. C.; Ahmed, H.

doi:10.1016/s0167-9317(02)00432-x

Cited by 4 publications

(3 citation statements)

References 9 publications

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“…The energetics of the different domain wall types are analysed further in [51] as well. In addition to the vortex and onion states, that are found at remanence, very wide rings in an applied field also exhibit an additional 'vortexcore' state, where a complete vortex core is present in the ring as seen in the micromagnetic simulation in figure 17 and explained in detail in [24].…”

Section: Observation Of Magnetic States In Ringsmentioning

confidence: 87%

“…When the Co is deposited, the edge profile changes slope, defining a trapezoid-shaped cross-section. The EELS measurements prove quantitatively that no direct exchange between the Co on the summits and in the trenches exists [24]. This means that by using prepatterned substrates, individual free-standing epitaxial rings can be fabricated.…”

Section: Physical Separation Between Rings and The Trenchesmentioning

confidence: 89%

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Vortex formation in narrow ferromagnetic rings

Kläui

Vaz

López-Dı́az

et al. 2003

J. Phys.: Condens. Matter

258

228

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The high-symmetry ring geometry is shown to exhibit a wide range of intriguing magnetostatic and magnetodynamic properties, which we survey in this topical review. We consider first the patterning and deposition techniques, which are used to fabricate ring structures (diameters between 0.1 and 2 µm) and discuss their respective advantages and disadvantages. The results of direct nanoscale imaging of the novel magnetization configurations present in rings with different geometrical parameters (including discs) are discussed. These results give valuable insight into the influence of the magnetic anisotropies governing the magnetic states. The different types of domain walls that arise are compared quantitatively to micromagnetic simulations. The magnetodynamic switching between the different magnetic states is described in detail. In particular we elaborate on the different geometry-dependent magnetic switchings, since the different transitions occurring allow us to determine which energy terms govern the reversal process. We discuss a process by which fast (sub-ns) and controlled switching can be achieved, therefore making rings an attractive geometry for applications, in addition to studying fundamental issues of nanomagnetism.

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Section: Observation Of Magnetic States In Ringsmentioning

confidence: 87%

Section: Physical Separation Between Rings and The Trenchesmentioning

confidence: 89%

Vortex formation in narrow ferromagnetic rings

Kläui

Vaz

López-Dı́az

et al. 2003

J. Phys.: Condens. Matter

258

228

View full text Add to dashboard Cite

show abstract

“…These were fully coated with a gold layer by depositing the gold at an angle while rotating the sample. The details of the growth are described in [14].…”

mentioning

confidence: 99%

Anisotropy engineering in Co nanodiscs fabricated using prepatterned silicon pillars

Thirion¹,

Wernsdorfer²,

Kläui³

et al. 2006

Nanotechnology

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Magnetic nanodiscs are fabricated by depositing cobalt onto 10-30 nm diameter silicon nanopillars, which were prepatterned using gold colloids as etch masks. The magnetic anisotropy energy of individual nanodiscs is studied by measuring the angular dependence of switching field using the micro-SQUID technique. The Stoner-Wohlfarth model, describing the magnetization reversal by unifom rotation, is used to analyse the data. The switching astroids of pure Co exhibit a cubic magnetocrystalline anisotropy indicating that the Co crystallites are fcc. After controlled oxidation of the nanoparticles, the anisotropy is dominated by a defect-induced uniaxial anisotropy, which means that the anisotropy can be used as a quality gauge.Understanding and engineering magnetic anisotropies is critically important in magnetic nanostructures, since they govern both the static and dynamic physical properties of such systems. The effective anisotropy, which determines the easy and hard magnetization directions is a superposition of different contributions including magnetocrystalline, surface and shape anisotropy [1]. Some of these terms can be tailored, such as the magnetocrystalline anisotropy by choosing the material and the shape anisotropy by selecting a geometry. Other anisotropy terms are related to defects, such as misf t dislocations and local oxidation spots. These anisotropies tend to be uniaxial, while the other ones can be engineered to be of higher order, such as cubic. A direct measurement of the individual anisotropy contributions is usually not possible in nanoparticle systems. However, the entire anisotropy function is measurable via the three-dimensional critical surface of the switching f elds [2]. Since our measurement of the famous Stoner-Wohlfarth astroid [3] on a single nanoparticle, we have investigated different particles from 40 nm barium ferrite to 3 nm cobalt nanoparticles [4][5][6][7][8]. One of the intriguing questions that emerged when we tried to engineer the anisotropies was why the observed anisotropies always had a prevalent uniaxial anisotropy. This observation was contrary to expectations that small fcc Co particles, which we studied, should exhibit a pure cubic magnetocrystalline anisotropy. For applications, the key task is designing anisotropies, since for applications such as memory devices, the anisotropies determine the minimum bit size which is thermally stable [9,10]. Such design is possible if the anisotropy is determined by the choice of materials and crystallographic phase rather than by defects, which are inherently hard to control. Thus the key question is whether the observed uniaxial anisotropy stems from defects or whether it corresponds to the inherent anisotropy of the system. To unambiguously demonstrate that the anisotropies can be engineered in single domain particles, and are not defect dominated, a system has to be devised which exhibits a pure higher-order anisotropy. Even for the simplest case, which is the cubic anisotropy, so far no results on single domain pa...

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Magnetization Configurations and Reversal in Small Magnetic Elements

Kläui

Vaz

2007

Handbook of Magnetism and Advanced Magnetic Materials

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This chapter presents an overview of the magnetization configurations and reversal in magnetic structures ranging from a few nanometers to a few micrometers in size that can be described using the theory of micromagnetics. A range of techniques for the characterization of magnetic structures is introduced and the theoretical micromagnetism background, including the energy terms governing the magnetic properties, are discussed. The simplest case of a single domain system with uniform magnetization is treated within the framework of the Stoner–Wohlfarth theory, and experimental examples of such systems are presented. The magnetization configurations in larger systems that exhibit nonuniform magnetization are discussed in detail with a particular emphasis on experimental examples for the geometries that have been studied most often, such as discs, rings, rectangles, wires and pillars. Theoretically, the formation of these states is explained as a result of the interplay between the different magnetic energy terms; multidomain states that occur for larger elements are also introduced. The dynamic properties of the reversal of these elements are addressed, starting with the evaluation of the Landau–Lifshitz–Gilbert equation to obtain the trajectories for single domain particles. This is then extended to cover the nonhomogeneous reversal of nonuniform states. The elementary processes occurring during nonhomogeneous reversal are introduced and used to explain the magnetization reversal in a set of instructive examples.

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Fabrication and magnetic properties of prepatterned epitaxial nanodots

Cited by 4 publications

References 9 publications

Vortex formation in narrow ferromagnetic rings

Vortex formation in narrow ferromagnetic rings

Anisotropy engineering in Co nanodiscs fabricated using prepatterned silicon pillars

Magnetization Configurations and Reversal in Small Magnetic Elements

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