Magnetotransport properties of high-quality cobalt nanowires grown by focused-electron-beam-induced deposition

Fernández-Pacheco, Amalio; Teresa, J. M. De; Córdoba, R.; Ibarra, M. R.

doi:10.1088/0022-3727/42/5/055005

Cited by 156 publications

(244 citation statements)

References 38 publications

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“…Drawing any conclusions about the absolute coercive field strength would be elusive, because only one nanowire of each kind was measured in this case and the switching field distribution of single wires spread on a wafer can be surprisingly large due to defects and irregularities [14]. The nanowires show linear, metallic R vs T behaviors with residual resistivity ratios of (300 )/ (2 ) ≈ 4.5, which is a notably high value for electrodeposited, ferromagnetic nanowires [27,36,59,60], indicating a good sample quality (see supporting information).…”

Section: Properties Of Individual Nanomagnetsmentioning

confidence: 98%

Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

Sergelius¹,

Lee²,

Fruchart³

et al. 2017

Nanotechnology

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Segmented magnetic nanowires are a promising route for the development of three dimensional data storage techniques. Such devices require a control of the coercive field and the coupling mechanisms between individual magnetic elements. In our study, we investigate electrodeposited nanomagnets within host templates using vibrating sample magnetometry and observe a strong dependence between nanowire length and coercive field (25 nm to 5 µm) and diameter (25 nm to 45 nm). A transition from a magnetization reversal through coherent rotation to domain wall propagation is observed at an aspect ratio of approximately 2. Our results are further reinforced via micromagnetic simulations and angle dependent hysteresis loops. The found behavior is exploited to create nanowires consisting of a fixed and a free segment in a spin-valve like structure. The wires are released from the membrane and electrically contacted, displaying a giant magnetoresistance effect that is attributed to individual switching of the coupled nanomagnets. We develop a simple analytical model to describe the observed switching phenomena and to predict stable and unstable regimes in coupled nanomagnets of certain geometries.-2 - INTRODUCTIONIn the investigation of nanomagnet assemblies, the focus has mainly been on lithographicallypatterned, planar structures, which can be used as logic devices capable of executing Boolean logic operations [1][2][3][4][5][6][7][8]. Often applications are sought within high density recording, bit patterned media [9][10][11][12] or MRAM devices [1,13], however since the bit size of modern hard disk drives (approx. 20x20 nm²) is already lower than what is achievable with most lithography techniques [14], potential use is limited. Therefore, the use of the third dimension is an appealing approach. Studies on alternating, vertical stacks of magnetic and non-magnetic materials have already been published, in which a three dimensional shift register is investigated, that is capable of storing and shifting several bits of information as solitons within a single column [15][16][17][18][19]. These shift registers are coupled via RKKY interaction and its oscillatory nature allows for an additional degree of freedom in the design of the device, but as a drawback the samples are very demanding with regard to sample quality and purity. A soliton, which is the bearer of information, is a magnetic frustration within a 1D chain of magnetic moments. It is thinkable to induce such a soliton using dipolar coupling instead of RKKY, simply by magnetizing two nanomagnets in the same direction and placing them next to each other (transversal soliton [20]). Another possibility would be to magnetize them in opposing direction and place them in a head-to-head or tail-to-tail configuration (longitudinal soliton, Figure 1). The coupling strength is then defined by the material properties and the distance of both nanomagnets. Such kinds of nanowires can be synthesized within porous anodic aluminum oxide (AAO) templates [21-23] using electro...

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Section: Properties Of Individual Nanomagnetsmentioning

confidence: 98%

Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

Sergelius¹,

Lee²,

Fruchart³

et al. 2017

Nanotechnology

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“…22 In a recent work, high purity Co NWs of lateral size down to 30 nm were produced by FEBID. 20 Though the magnetic characterization of this type of systems has been carried out up to now by multiple indirect techniques, such as resistivity, magnetoresistance, Hall effect, magneto-optical Kerr effect, and electron microscopy, 19,20,[23][24][25] direct observation of the magnetic configurations and magnetization processes with high spatial a) …”

mentioning

confidence: 99%

“…Particularly cobalt (Co) nanostructures have been obtained with purities up to 95% so these deposits present optimal properties matching those of the bulk counterpart. 19,20 Furthermore, as the electron beam producing the deposition can be simply scanned upon the surface, nanostructures of various different shapes and size can be easily produced. 20 The FEBID spatial resolution is also very high, down to 3 nm in the case of Pt deposits, 21 so this technique is capable of producing nanostructures with very fine details such as constrictions, needle shape tips, etc.…”

mentioning

confidence: 99%

“…The growth parameters to achieve high purity (>90%) Co structures have been optimized in previous works and a detailed description can be found elsewhere. 19 The Co structures have been grown on electron-transparent 50-nm-thick Si 3 N 4 membranes, which are suitable for magnetic imaging in transmission experiments using electrons 20 or x-rays. 22 The lengths of the two branches of the NWs were fixed for all the objects to 3.5 lm and 8.5 lm for the short and long branches, respectively.…”

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confidence: 99%

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Optimized cobalt nanowires for domain wall manipulation imaged by in situ Lorentz microscopy

Rodríguez

Magén

Snoeck

et al. 2013

Applied Physics Letters

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Direct observation of domain wall (DW) nucleation and propagation in focused electron beam induced deposited Co nanowires as a function of their dimensions was carried out by Lorentz microscopy (LTEM) upon in situ application of magnetic field. Optimal dimensions favoring the unambiguous DW nucleation/propagation required for applications were found in 500-nm-wide and 13-nm-thick Co nanowires, with a maximum nucleation field and the largest gap between nucleation and propagation fields. The internal DW structures were resolved using the transport-ofintensity equation formalism in LTEM images and showed that the optimal nanowire dimensions correspond to the crossover between the nucleation of transverse and vortex walls. In the last decade, several pioneering works envisaged different strategies to design magnetic information storage, logic devices or sensors based on magnetic domain walls (DW) as functional entities to store, transfer, and process information in ferromagnetic media. [1][2][3][4][5] These innovative ideas and promising applications have motivated extensive developments of ferromagnetic nanostructures in which DW can be "easily" created and driven either by external magnetic fields and/or spin-polarized currents. 6-12 DW in magnetic nanostructures have therefore become a major topic for the research community in the field of Nanomagnetism. The specific DW configuration is the result of the balance between the magnetostatic energy, the magnetocrystalline anisotropy, and the exchange coupling. Therefore, along with the intrinsic properties of the magnetic material, it also depends on the geometry and the dimensions of the nanostructures. 13 In magnetic nanowires (NWs), the possible DW configurations are either symmetric or asymmetric transverse walls (TWs) or vortex walls (VWs) and they move differently under the application of an external magnetic field or current. 14 Therefore, a careful analysis of the DW structure of devices as a function of dimensions, geometries, shape of constrictions, etc. is requested to determine the type of magnetic configurations appearing in a given nanostructure and the possibility of tuning and manipulating them upon the application of external magnetic fields or electric currents. 6,8,[10][11][12] Permalloy (Py) nanostructures have been extensively studied because of their low magnetocrystalline anisotropy, thus allowing the control of its magnetic properties simply adjusting its shape anisotropy. Therefore, many Py nanostructures of various shapes and sizes have been synthetized using electron beam or UV lithography processes. [1][2][3][4][5][6][7][8][9][10][11][12]15,16 The use of ferromagnetic materials alternative to Py and the development of advanced nanofabrication methods allowing creating magnetic nanostructures of dimensions less than 100 nm are however needed to explore their functionalities and possible applications. In the last years, focused electron beam induced deposition (FEBID) technique has demonstrated a capacity to produce high quality nanostructu...

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“…Focused-electron-beam-induced deposition of magnetic Co (FEBID-Co) and focused-ionbeam-induced deposition of superconducting W (FIBID-W) are made following previous work. [8][9][10] Nanocontacts are obtained by suitably nanoshaping the Co-based magnetic deposit into a sharp tip-like structure, contacting the W-based superconductor. Importantly, the two electrodes forming the contact are grown under high vacuum, minimizing oxidation during contact formation.…”

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confidence: 99%

Andreev reflection under high magnetic fields in ferromagnet-superconductor nanocontacts

et al. 2011

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We study the magnetic-field dependence of the conductance in planar ferromagnet-superconductor nanocontacts created with focused-electron/ion-beam techniques. From the fits of the differential conductance curves in high magnetic fields, we obtain the magnetic field dependences of the superconducting gap and the broadening parameter. Orbital depairing is found to be linear with magnetic field. We evaluate the magnetic field dependence of the quasiparticle density of states, and we compare it with the value obtained by scanning tunneling spectroscopy experiments. The study of the differential conductance (that is the first derivative of the I-V characteristic, dI/dV) of point contacts has been demonstrated to be an effective tool to probe the interaction mechanisms in conductive materials: inelastic scattering of electrons by phonons, 1 scattering of electrons by magnons, 2 etc. If one of the electrodes forming the point contact is superconductor, through the study of the Andreev reflection 3 (AR) occurring at the interface it is possible to obtain information on the superconducting gap. In ferromagnet-superconductor point contacts, along with the information on the superconductor gap, the ferromagnet spin polarization can be extracted, 4,5 making this type of study very appealing.The superconductor density of states under magnetic field is a relevant parameter in basic studies of superconductivity as well as in applications where the superconductor is under the influence of high magnetic fields. AR measurements in a magnetic field provide further information on the properties of the superconducting 6 and ferromagnetic electrodes of the contact. So far no systematic investigations of ferromagnetsuperconductor nanocontacts under high magnetic fields have been carried out. A comprehensive study of the effect of a magnetic field on the transport properties of ferromagnetsuperconductor nanocontacts is due to 7 and the maximum magnetic field applied in this study is 16.5 mT, since the critical field of the Al electrode used as the superconducting electrode is 15 mT. In this Brief Report, we propose a different approach to evaluate the magneticfield dependence of the quasiparticle density of states of superconductors from the measurement of the conductance in high magnetic fields.The nanocontacts are created between a superconducting W nanodeposit and a magnetic Co nanodeposit under high vacuum conditions using commercial dual beam equipment that integrates a focused electron column and a focused Ga ion column forming 52 degrees. Focused-electron-beam-induced deposition of magnetic Co (FEBID-Co) and focused-ionbeam-induced deposition of superconducting W (FIBID-W) are made following previous work. [8][9][10] Nanocontacts are obtained by suitably nanoshaping the Co-based magnetic deposit into a sharp tip-like structure, contacting the W-based superconductor. Importantly, the two electrodes forming the contact are grown under high vacuum, minimizing oxidation during contact formation. The in situ monitoring of the resista...

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Magnetotransport properties of high-quality cobalt nanowires grown by focused-electron-beam-induced deposition

Cited by 156 publications

References 38 publications

Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

Optimized cobalt nanowires for domain wall manipulation imaged by in situ Lorentz microscopy

Andreev reflection under high magnetic fields in ferromagnet-superconductor nanocontacts

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