Noninvasive magnetic imaging and magnetization measurement of isolated mesoscopic Co rings

Bekaert, Joost; Buntinx, D.; Haesendonck, Chris Van; Moshchalkov, Victor; Boeck, J. De; Borghs, Gustaaf; Metlushko, V.

doi:10.1063/1.1518564

Cited by 41 publications

(29 citation statements)

References 11 publications

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“…As such, the magnetic signal of the magnetic nanorings has been too weak for full characterization using magnetometry. Instead, the magnetic characteristics have been measured or inferred by surface magneto-optic Kerr effect (MOKE) measurements, [17,19] resistance measurements, [18,22] Hall-sensor measurements, [20,24] and magnetic force microscopy. [21] In these cases, the external applied magnetic field could only be applied in certain directions, and not all, so as not to interfere with the specific measuring technique used.…”

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confidence: 99%

Ultrahigh‐Density Arrays of Ferromagnetic Nanorings on Macroscopic Areas

Zhu¹,

et al. 2004

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In conclusion, we have demonstrated a hybrid-memory device where information can be introduced optically and can be extracted or erased electrically. We expect much improved performance, in terms of retention, stability, and operating voltages upon introducing intentional electron-trapping centers in dilute proportions in the semiconducting-polymer matrix, along with optimization of geometrical parameters. ExperimentalThe top-contact geometry, as shown in Figure 1a, was used to fabricate the polymer field-effect transistor devices based on poly(3-hexylthiophene) (P3HT) [7]. Regioregular P3HT was obtained from Aldrich Inc., and was re-purified using standard procedures (re-precipitation method). Our samples and devices were handled in a glove box (MBraun, Inc.), and stringent procedures were observed to ensure the quality of the devices. A transparent water-soluble dielectric (polyvinyl alcohol, e » 8) layer with a thickness of 0.5 lm was spincoated on top of an aluminum-coated glass substrate. The dielectric surface was then treated using standard established procedures using hexamethyldisilazane. A layer of regioregular P3HT (thickness » 150 nm) was spin-coated (1500 rpm) from chloroform solution on the insulator under an inert atmosphere, followed by a thermal treatment under vacuum at 60 C for 24 h. The drain and source electrodes with a separation of 25±40 lm (L) and width of 2 mm (W) were deposited by thermal evaporation of gold using a shadow mask. All the experiments were performed under vacuum (10 ±1 Pa).

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confidence: 99%

Ultrahigh‐Density Arrays of Ferromagnetic Nanorings on Macroscopic Areas

Zhu¹,

et al. 2004

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“…The recent process in nanopatterning has made it possible to fabricate very sensitive Hall sensors made from the GaAs/AlGaAs semiconductor heterostructure containing a two-dimensional electron gas. These Hall sensors and Hall magnetometers have been efficiently used for characterization of both ferromagnetic 16,17 and superconducting 18 materials as well as for local visualization of the magnetic field profile 17 in a non-invasive way. A submicron superconducting or ferromagnetic element can be deposited on the sensitive area of the probe.…”

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confidence: 99%

Influence of sample geometry on vortex matter in superconducting microstructures

2004

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The dependence of the vortex penetration and expulsion on the geometry of mesoscopic superconductors is reported. Hall magnetometry measurements were performed on a superconducting Al square and triangle. The stability of the vortex patterns imposed by the sample geometry is discussed. The field-temperature H − T diagram has been reconstructed showing the transitions between states with different vorticity. We have found that the vortex penetration is only weakly affected by the vortex configuration inside the sample while the expulsion is strongly controlled by the stability of the vortex patterns. A qualitative explanation for this observation is given.

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“…12 In contrast to the switching processes, which have been studied for all ring widths ranging from very narrow rings with a ratio of inner to outer diameter of 1/1.3 to very wide rings with a ratio of 1/6, 13 the magnetic states have so far only been directly determined for narrow rings ͑ratios between 1/1.3 and 1/3͒ and for disks. 5,8,10,12,20,21 In disks there is no direct equivalence for the onion state in rings, but rather a number of possible states ͑c state, s state, etc.͒. Thence a key question, which so far has not been addressed, is whether these states are confined to disks or whether they are also present in sufficiently wide rings.…”

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“…Narrow magnetic rings have shown to be a useful geometry, since particularly well-defined states are observed and the switching between these states has been found to be reproducible, simple, and fast. [3][4][5][6][7][8][9][10][11][12] In most of the ring geometries investigated so far, micromagnetic simulations and magnetization measurements show the existence of two magnetic states: 3,4,10,12 the flux-closure vortex state and the "onion" state, accessible reversibly from saturation and characterized by the presence of two opposite head-to-head walls. In narrow magnetic rings the magnetic states and the switching have been thoroughly studied, [3][4][5][6]12,13 with particular emphasis on the head-to-head domain walls present in the onion state.…”

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Magnetic states in wide annular structures

Kläui

Rüdiger

Vaz

et al. 2006

Journal of Applied Physics

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The results of nonintrusive high-resolution imaging of the magnetic states present in wide Co rings with a small inner hole ͑1.7 m outer diameter, 300 nm inner diameter, and 700 nm width͒ are presented. Rather than the reproducible onion state commonly found in rings, a prevalent triangle state is observed, with other magnetic states characteristic of disks also occurring. The uniformity and the magnetic states in these wide rings are found to be more typical of disks than of rings. Analyzing the energetics of the formation of the magnetic states, this is attributed to the reduced shape anisotropy in wide rings as compared to narrow rings.The evolution of devices to smaller and smaller scales has fueled an increasing research interest in mesoscopic magnetic elements. In addition to insights into the underlying physical principles, mesoscopic structures have shown a potential for a range of applications in nanotechnology. These applications include memory elements in high-density storage media or miniaturized sensor elements. 1,2 Intensive research has been devoted to understanding and, in particular, controlling the magnetic properties of small ferromagnetic elements. A key issue is the magnetic switching, since this determines whether a magnetic nanostructure can be utilized in applications. Narrow magnetic rings have shown to be a useful geometry, since particularly well-defined states are observed and the switching between these states has been found to be reproducible, simple, and fast. [3][4][5][6][7][8][9][10][11][12] In most of the ring geometries investigated so far, micromagnetic simulations and magnetization measurements show the existence of two magnetic states: 3,4,10,12 the flux-closure vortex state and the "onion" state, accessible reversibly from saturation and characterized by the presence of two opposite head-to-head walls. In narrow magnetic rings the magnetic states and the switching have been thoroughly studied, [3][4][5][6]12,13 with particular emphasis on the head-to-head domain walls present in the onion state. 12,14 In disks and similar topologically simply connected elements ͑ellipses, rectangles, etc.͒, in addition to the vortex state, more complex states ͑s state, c state, and triangle state͒ have been predicted and observed. [15][16][17][18][19][20] A consequence of the existence of different magnetic states with similar energies in disks is that after subjecting an array of nominally identical disks to the same field history, disks are found in different magnetic states. 20 This is due to small edge irregularities or film defects, which cause energy barriers between the metastable states and the ground state. In narrow rings with a limited number of magnetic states, good reproducibility and uniformity of the magnetic states across an array have been observed. 21

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Noninvasive magnetic imaging and magnetization measurement of isolated mesoscopic Co rings

Cited by 41 publications

References 11 publications

Ultrahigh‐Density Arrays of Ferromagnetic Nanorings on Macroscopic Areas

Ultrahigh‐Density Arrays of Ferromagnetic Nanorings on Macroscopic Areas

Influence of sample geometry on vortex matter in superconducting microstructures

Magnetic states in wide annular structures

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