Magnetization reversal in single-layer and exchange-biased elliptical-ring arrays

Castaño, Fernando; Morecroft, D.; Ross, Caroline A.; Menon, Rajesh; Smith, Henry I.

doi:10.1063/1.1855461

Cited by 23 publications

(19 citation statements)

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“…Investigations of the role of magnetic vortices in exchange bias systems have begun only recently [27][28][29][30][31]. In previous experiments, we have shown that the interplay between the unidirectional exchange bias and vortex structures can give rise to angular-dependent magnetization reversal, when the exchange bias is established with a saturated ferromagnet [27,31].…”

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Imprinting Vortices into Antiferromagnets

et al. 2006

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The effect of imprinting symmetric and displaced vortex structures into an antiferromagnetic material is investigated in micron-sized disks consisting of exchange coupled ferromagnetic-antiferromagnetic bilayers. The imprint of displaced vortices manifests itself by the occurrence of a new type of asymmetric hysteresis loops characterized by curved, reversible, central sections with nonzero remanent magnetization. Such an imprint is achieved by cooling the disks through the blocking temperature of the system in small fields. Micromagnetic simulations reveal that asymmetric vortexlike loops naturally result from the competition between the different energies involved in the system. DOI: 10.1103/PhysRevLett.97.067201 PACS numbers: 75.60.Jk, 75.50.Ee, 75.70.Cn In ferromagnets and antiferromagnets, there are often domains with differently ordered spin states observed instead of a single homogeneously long-range ordered region. It turns out that domain structures in antiferromagnetic (AFM) materials have been far less studied than domains in ferromagnets [1]. This is partially due to the fact that the staggered AFM spin structure with its lack of a net magnetization makes the detection of domains and domain walls more challenging [2,3]. Moreover, the physical properties of AFM domains differ significantly from ferromagnetic (FM) domains. Domains in a ferromagnet are generally determined by balancing magnetostatic with exchange and anisotropy energies. Thus, in nanostructured systems, ferromagnets can develop welldefined unusual spin states, such as magnetic vortices [4 -9]. The absence of a net magnetization in antiferromagnets means that magnetostatic energy is vanishing, and, therefore, domains in antiferromagnets are generally metastable, since typically the gain in configurational entropy is not sufficient to overcome domain wall energies. Without any direct explicit driver for domain formation, the AFM domains may originate from random nucleation of long-range order due to randomly distributed defects [10]. For these reasons, the formation and evolution of AFM domains remain a research area with many open questions.Nevertheless, domains in antiferromagnets have received increased attention recently due to their role in exchange bias, i.e., the shift of the hysteresis loop observed in FM-AFM coupled systems [11,12], which is a key ingredient in spintronic devices [13]. Many exchange biased systems exhibit unusual properties, one of which is a pronounced asymmetry in the hysteresis loop, caused by different irreversible reversal mechanisms on either side of the hysteresis loop [14 -18]. Since the ferromagnet and the antiferromagnet are exchange coupled, measurements of the FM behavior provide an indirect probe of the properties of the antiferromagnet, for example, the spin-flop field [19], the surface order parameter [20], the crystalline anisotropy [21], or the domain wall width [22,23]. Furthermore, it has recently been demonstrated that nonuniformly magnetized ferromagnets can modify the antiferromagnetic s...

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Imprinting Vortices into Antiferromagnets

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“…The samples have been fabricated specifically for PNR experiments by using zone plate array lithography [7], [9].…”

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confidence: 99%

“…3 and 4). The insets show a SEM image of small section of the sample [7], [9], and a schematic representation of the vortex and onion states. The red and blue arrows indicate the idealistic orientation of magnetization in the rings in each case.…”

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Polarized Neutron Reflectivity Investigation of Periodic Magnetic Rings

et al. 2007

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Magnetic ring structures are of particular interest, due to stable remanent configurations such as the vortex state, which have potential in future magnetic random access memory (MRAM) applications. Here we report results on the first experimental study of periodic ring arrays using off-specular polarized neutron reflectivity (PNR). The experiments were performed on a 7.5 mm 5 mm NiFe array with an average ring diameter of 3.2 m, 0.7 m width, 25 nm thickness, and separation of 5.6 m. Using polarization analysis, a spin dependent diffraction of reflected and transmitted neutron beams were investigated as a function of external applied field.Index Terms-Magnetic domains, magnetization reversal, polarized neutron reflectivity.

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“…Several fabrication methods for ordered arrays of ring-shaped structures have been developed. [13][14][15][17][18][19][20][21][22][23][24][25][26] Conventional structuring techniques such as photo-and electron-beam lithography (EBL) are limited in spatial resolution and low throughput, respectively. Alternatively, low-cost template-based synthesis approaches for ring-shaped nanostructures have been developed very recently.…”

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Templated Fabrication of Nanowire and Nanoring Arrays Based on Interference Lithography and Electrochemical Deposition

Lee

Scholz

et al. 2006

Advanced Materials

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Lithographically defined arrays of metallic or semiconductor nanorings with feature sizes in the sub-100 nm range have attracted great attention recently, because of their unique magnetic, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] optical, [16] or electrical properties. Several fabrication methods for ordered arrays of ring-shaped structures have been developed. [13][14][15][17][18][19][20][21][22][23][24][25][26] Conventional structuring techniques such as photo-and electron-beam lithography (EBL) are limited in spatial resolution and low throughput, respectively. Alternatively, low-cost template-based synthesis approaches for ring-shaped nanostructures have been developed very recently. For example, arrays of metallic nanorings have been fabricated via self-assembled polymeric nanospheres positioned on planar substrates. In this case, metallic thin films were first deposited onto the nanospheres. Subsequently, the metallic nanorings were obtained by ion-beam bombardment and removal of the microspheres. [18][19][20][21][22] However, the arrangement of the nanorings fabricated by these approaches is often random, or ordered in small areas only when self-ordering strategies have been applied for the nanosphere assembly. Membrane structures were also utilized for the fabrication of ring arrays such as porous anodic aluminum oxide (AAO) [23,24] and nanochannel glass (NCG).[25]They are scalable and suitable for the fabrication of large, ordered arrays of circular nanorings. On the other hand, the template preparation on a large scale is not straightforward. In the last two years, much attention has been drawn towards elliptical magnetic rings [13][14][15] with an in-plane magnetic anisotropy for potential application in magnetic random access memory (MRAM) devices. These magnetic nano-objects have been intensively investigated by the C. A. Ross group at Massachusetts Institute of Technology and were generated by conventional EBL. Except for conventional lithography techniques, no efficient fabrication method has been reported so far on large-scale arrays of elliptical ring structures. A very different fabrication approach for lateral nanowire arrays based on a bottom-up technique called electrochemical step edge decoration (ESED) has recently been reported by Penner and co-workers. [27][28][29][30] Highly oriented pyrolytic graphite (HOPG) was used as a template substrate for electrochemical deposition of hemicylindrical nanowires on the atomic step edges with diameters ranging from 10 nm to 1 lm. However, the step edges of HOPG are not perfectly aligned; therefore electrodeposition of perfectly ordered nanowire arrays is not feasible. Furthermore, deposition of nanoparticles occurs frequently on the graphite terraces.Here we report a large-scale fabrication technique for ideally ordered lateral metallic nanowire or nanoring arrays over wafer-scale areas. Our approach is based on the generation of Si 3 N 4 nanohole arrays or grating structures on silicon wafers by laser interference lithography (LIL) and th...

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Magnetization reversal in single-layer and exchange-biased elliptical-ring arrays

Cited by 23 publications

References 19 publications

Imprinting Vortices into Antiferromagnets

Imprinting Vortices into Antiferromagnets

Polarized Neutron Reflectivity Investigation of Periodic Magnetic Rings

Templated Fabrication of Nanowire and Nanoring Arrays Based on Interference Lithography and Electrochemical Deposition

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