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Paschoal Jr., WaldomiroORCID iD iconorcid.org/0000-0002-2348-1244
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Publications (9 of 9) Show all publications
Johannes, A., Noack, S., Paschoal Jr., W., Kumar, S., Jacobsson, D., Pettersson, H., . . . Ronning, C. (2015). Corrigendum: Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires (2014 J. Phys. D: Appl. Phys. 47 394003). Journal of Physics D: Applied Physics, 48(7), Article ID 079501.
Open this publication in new window or tab >>Corrigendum: Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires (2014 J. Phys. D: Appl. Phys. 47 394003)
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2015 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 48, no 7, article id 079501Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Bristol: Institute of Physics Publishing (IOPP), 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:hh:diva-35703 (URN)10.1088/0022-3727/48/7/079501 (DOI)000348842800009 ()2-s2.0-84961292028 (Scopus ID)
Available from: 2018-02-06 Created: 2018-02-06 Last updated: 2018-04-03Bibliographically approved
Johannes, A., Noack, S., Paschoal Jr, W., Kumar, S., Jacobsson, D., Pettersson, H., . . . Ronning, C. (2014). Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires. Journal of Physics D: Applied Physics, 47(39), Article ID 394003.
Open this publication in new window or tab >>Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires
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2014 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, no 39, article id 394003Article in journal (Refereed) Published
Abstract [en]

We simulated and experimentally investigated the sputter yield of ZnO and GaAs nanowires, which were implanted with energetic Mn ions at room temperature. The resulting thinning of the nanowires and the dopant concentration with increasing Mn ion fluency were measured by accurate scanning electron microscopy (SEM) and nano-x-Ray Fluorescence (nanoXRF) quantification, respectively. We observed a clearly enhanced sputter yield for the irradiated nanowires compared to bulk, which is also corroborated by iradina simulations. These show a maximum if the ion range matches the nanowire diameter. As a consequence of the erosion thinning of the nanowire, the incorporation of the Mn dopants is also enhanced and increases non-linearly with increasing ion fluency. © 2014 IOP Publishing Ltd.

Place, publisher, year, edition, pages
Bristol: Institute of Physics Publishing (IOPP), 2014
Keywords
Ion implantation, nanowires, sputtering
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:hh:diva-27512 (URN)10.1088/0022-3727/47/39/394003 (DOI)000341772000005 ()2-s2.0-84922124528 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

The authors gratefully acknowledge funding by the German Research Society (DFG) within the DACH project. We thank the European Synchrotron Radiation Facility (ESRF) for the allocated beam-time.The authors acknowledge financial support from the Nanometer Structure Consortium at Lund University (nmC@LU), the Swedish Research Council (VR), and the Knut and Alice Wallenberg Foundation (KAW).

Available from: 2015-01-19 Created: 2015-01-19 Last updated: 2018-04-03Bibliographically approved
Paschoal Jr., W., Kumar, S., Jacobsson, D., Johannes, A., Jain, V., Canali, C. M., . . . Pettersson, H. (2014). Magnetoresistance in Mn ion-implanted GaAs:Zn nanowires. Applied Physics Letters, 104(15), Article ID 153112.
Open this publication in new window or tab >>Magnetoresistance in Mn ion-implanted GaAs:Zn nanowires
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2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 15, article id 153112Article in journal (Refereed) Published
Abstract [en]

We have investigated the magnetoresistance (MR) in a series of Zn doped (p-type) GaAs nanowires implanted with different Mn concentrations. The nanowires with the lowest Mn concentration (~0.0001%) exhibit a low resistance of a few kΩ at 300K and a 4% positive MR at 1.6K, which can be well described by invoking a spin-split subband model. In contrast, nanowires with the highest Mn concentration (4%) display a large resistance of several MΩ at 300K and a large negative MR of 85% at 1.6K. The large negative MR is interpreted in terms of spin-dependent hopping in a complex magnetic nanowire landscape of magnetic polarons, separated by intermediate regions of Mn impurity spins. Sweeping the magnetic field back and forth for the 4% sample reveals a hysteresis that indicates the presence of a weak ferromagnetic phase. We propose co-doping with Zn to be a promising way to reach the goal of realizing ferromagnetic Ga1-xMnxAs nanowires for future nanospintronics. © 2014 AIP Publishing LLC.

Place, publisher, year, edition, pages
New York: American Institute of Physics (AIP), 2014
Keywords
Nanospintronics, Ion-implantation, GaMnAs, Nanowires, hopping transport, Negative magnetoresistance
National Category
Natural Sciences
Identifiers
urn:nbn:se:hh:diva-25126 (URN)10.1063/1.4870423 (DOI)000335145200060 ()2-s2.0-84899622402 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research
Note

W. Paschoal, Jr. and S. Kumar contributed equally to this work and are co-first authors. The authors acknowledge financial support from nmC@LU, the Swedish Research Council (VR), the Knut and Alice Wallenberg Foundation, the Swedish National Board for Industrial, Technological Development, the Swedish Foundation for Strategic Research, the Nordforsk research network “Nanospintronics; theory and simulations,” and the German Research Society (DFG) Project Ro1198/14. One of the authors, W.P., Jr., gratefully acknowledges financial support from the Pará Education Secretary (SEDUC) and the Pará Government School (EGPA).

Available from: 2014-04-22 Created: 2014-04-22 Last updated: 2018-04-03Bibliographically approved
Kumar, S., Paschoal, W., Johannes, A., Jacobsson, D., Borschel, C., Pertsova, A., . . . Pettersson, H. (2013). Magnetic Polarons and Large Negative Magnetoresistance in GaAs Nanowires implanted with Mn Ions [Letter to the editor]. Nano letters (Print), 13(11), 5079-5084
Open this publication in new window or tab >>Magnetic Polarons and Large Negative Magnetoresistance in GaAs Nanowires implanted with Mn Ions
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2013 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, no 11, p. 5079-5084Article in journal, Letter (Refereed) Published
Abstract [en]

We report on low-temperature magnetotransport and SQUID measurements on heavily doped Mn-implanted GaAs nanowires. SQUID data recorded at low magnetic fields exhibit clear signs of the onset of a spin-glass phase with a transition temperature of about 16 K. Magnetotransport experiments reveal a corresponding peak in resistance at 16 K and a large negative magnetoresistance, reaching 40% at 1.6 K and 8 T. The negative magnetoresistance decreases at elevated temperatures and vanishes at about 100 K. We interpret our transport data in terms of spin-dependent hopping in a complex magnetic nanowire landscape of magnetic polarons, separated by intermediate regions of Mn impurity spins, forming a paramagnetic/spin-glass phase. Copyright © 2013 American Chemical Society

Place, publisher, year, edition, pages
Washington, United States: American Chemical Society (ACS), 2013
Keywords
Nanospintronics, Ion-implantation, GaMnAs, Nanowires, hopping transport, Negative magnetoresistance
National Category
Physical Sciences
Identifiers
urn:nbn:se:hh:diva-25041 (URN)10.1021/nl402229r (DOI)000327111700014 ()24093475 (PubMedID)2-s2.0-84887830532 (Scopus ID)
Funder
Swedish Foundation for Strategic Research
Available from: 2014-04-14 Created: 2014-04-14 Last updated: 2018-04-03Bibliographically approved
Paschoal Jr., W., Kumar, S., Borschel, C., Borgström, M., Ronning, C., Canali, C., . . . Pettersson, H. (2012). Electron transport in Mn+ implanted GaAs nanowires. In: : . Paper presented at 31st International Conference on the Physics of Semiconductors (ICPS 2012), Zürich, Switzerland, July 29-August 3, 2012.
Open this publication in new window or tab >>Electron transport in Mn+ implanted GaAs nanowires
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2012 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

Mn-doped GaAs semiconductors have generated great interest in current research regarding the evolution from a paramagnetic insulator to a ferromagnetic metal governed by a carrier mediated exchange interaction. The interplay between the charge carriers in a semiconductor and the electron spin of incorporated ferromagnetic metals can be utilized for novel spin-sensitive spintronic devices. We have fabricated highly Mn-doped, single-crystalline GaAs nanowires (NWs) by ion implantation at elevated temperatures to facilitate in-situ dynamic annealing. To exploit these nanowires in spintronic applications, a detailed understanding of fundamental charge transport mechanisms is however necessary. It is generally expected that new features, different from any bulk counterparts, will emerge in systems with reduced dimensionality e.g. quasi-1D NWs. Here we report on a detailed study of different charge transport mechanisms and localization-related effects in single Mn-doped GaAs NWs in the temperature range from 300K to 1.6K, and with magnetic fields ranging from 0T to 8T. In general, the resistance of the nanowires increases strongly from a few M* at 300K to several G* at 1.6 K. More specially, the temperature dependence displays several different interesting regimes described by distinctly different models. Furthermore, the current-voltage (I-V) characteristics becomes strongly non-linear as the temperature decreases and shows apparent power-law behavior at low temperatures. In particular, we interpret our transport data in the temperature range from 80K to 275K in terms of a variable range hopping process influenced by Mn-induced disorder in the NWs. Below 50K the magnetotransport data reveals a large negative magnetoresistance (MR) under both paralleland perpendicular magnetic fields. We are presently developing models to explain this large MR signal, including low-temperature transport mechanisms and possible magnetic interaction between Mn ions.

Keywords
Spintronics and spin phenomena
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:hh:diva-19649 (URN)
Conference
31st International Conference on the Physics of Semiconductors (ICPS 2012), Zürich, Switzerland, July 29-August 3, 2012
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationThe nanometer Structure Consortium at Lund University
Available from: 2012-09-18 Created: 2012-09-17 Last updated: 2018-04-03Bibliographically approved
Paschoal Jr., W., Kumar, S., Borschel, C., Wu, P., Canali, C. M., Ronning, C., . . . Pettersson, H. (2012). Hopping Conduction in Mn Ion-Implanted GaAs Nanowires [Letter to the editor]. Nano letters (Print), 12(9), 4838-4842
Open this publication in new window or tab >>Hopping Conduction in Mn Ion-Implanted GaAs Nanowires
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2012 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 12, no 9, p. 4838-4842Article in journal, Letter (Refereed) Published
Abstract [en]

We report on temperature-dependent charge transport in heavily doped Mn+ implanted GaAs nanowires.The results clearly demonstrate that the transport is governedby temperature-dependent hopping processes, with a crossoverbetween nearest neighbor hopping and Mott variable rangehopping at about 180 K. From detailed analysis, we haveextracted characteristic hopping energies and correspondinghopping lengths. At low temperatures, a strongly nonlinearconductivity is observed which reflects a modified hoppingprocess driven by the high electric field at large bias.

Place, publisher, year, edition, pages
Washington: American Chemical Society (ACS), 2012
Keywords
mott hopping, nanowires, self-assembly, ion-implantation, GaMnAs, spintronics
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:hh:diva-19647 (URN)10.1021/nl302318f (DOI)000308576000069 ()22889471 (PubMedID)2-s2.0-84866332692 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationThe nanometer Structure Consortium at Lund University
Available from: 2012-09-18 Created: 2012-09-17 Last updated: 2018-04-03Bibliographically approved
Wu, P. M., Paschoal Jr., W., Kumar, S., Borschel, C., Ronning, C., Canali, C. M., . . . Linke, H. (2012). Thermoelectric Characterization of Electronic Properties of GaMnAs Nanowires. Journal of Nanotechnology, 2012, Article ID 480813.
Open this publication in new window or tab >>Thermoelectric Characterization of Electronic Properties of GaMnAs Nanowires
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2012 (English)In: Journal of Nanotechnology, ISSN 1687-9503, E-ISSN 1687-9511, Vol. 2012, article id 480813Article in journal (Refereed) Published
Abstract [en]

Nanowires with magnetic doping centers are an exciting candidate for the study of spin physics and proof-of-principle spintronics devices. The required heavy doping can be expected to have a significant impact on the nanowires' electron transport properties. Here, we use thermopower and conductance measurements for transport characterization of Ga 0.95Mn 0.05As nanowires over a broad temperature range. We determine the carrier type (holes) and concentration and find a sharp increase of the thermopower below temperatures of 120 K that can be qualitatively described by a hopping conduction model. However, the unusually large thermopower suggests that additional mechanisms must be considered as well. © 2012 Phillip M. Wu et al.

Place, publisher, year, edition, pages
New York: Hindawi Publishing Corporation, 2012
Keywords
Thermoelectric, Hopping conduction model, Nanowires, GaMnAs
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:hh:diva-19650 (URN)10.1155/2012/480813 (DOI)2-s2.0-84867365396 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationThe nanometer Structure Consortium at Lund University
Available from: 2012-09-18 Created: 2012-09-17 Last updated: 2018-04-03Bibliographically approved
Borschel, C., Messing, M., Borgström, M. T., Paschoal, W., Wallentin, J., Kumar, S., . . . Ronning, C. (2011). A New Route toward Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions. Nano letters (Print), 11(9), 3935-3940
Open this publication in new window or tab >>A New Route toward Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions
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2011 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 9, p. 3935-3940Article in journal (Refereed) Published
Abstract [en]

We report on highly Mn-doped GaAs nanowires (NWs) of high crystalline quality fabricated by ion beam implantation, a technique that allows doping concentrations beyond the equilibrium solubility limit. We studied two approaches for the preparation of Mn-doped GaAs NWs: First, ion implantation at room temperature with subsequent annealing resulted in polycrystalline NWs and phase segregation of MnAs and GaAs. The second approach was ion implantation at elevated temperatures. In this case, the single-crystallinity of the GaAs NWs was maintained, and crystalline, highly Mn-doped GaAs NWs were obtained. The electrical resistance of such NWs dropped with increasing temperature (activation energy about 70 meV). Corresponding magnetoresistance measurements showed a decrease at low temperatures, indicating paramagnetism. Our findings suggest possibilities for future applications where dense arrays of GaMnAs nanowires may be used as a new kind of magnetic material system.

Place, publisher, year, edition, pages
Washington: American Chemical Society (ACS), 2011
Keywords
DMS, doping, dynamic annealing, GaAs, GaMnAs, ion-implantation, Nanospintronics, Nanowires
National Category
Natural Sciences
Identifiers
urn:nbn:se:hh:diva-16458 (URN)10.1021/nl2021653 (DOI)000294790200073 ()21848314 (PubMedID)2-s2.0-80052786045 (Scopus ID)
Available from: 2011-10-15 Created: 2011-10-15 Last updated: 2018-04-03Bibliographically approved
Borschel, C., Messing, M., Mergenthaler, K., Borgström, M. T., Paschoal, W., Wallentin, J., . . . Ronning, C. (2011). A New Route towards Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions. In: : . Paper presented at 2011 MRS Fall Meeting & Exhibit, 28 November – 2 December 2011, Boston, Massachusetts, US.
Open this publication in new window or tab >>A New Route towards Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions
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2011 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:hh:diva-22416 (URN)
Conference
2011 MRS Fall Meeting & Exhibit, 28 November – 2 December 2011, Boston, Massachusetts, US
Available from: 2013-06-04 Created: 2013-06-04 Last updated: 2018-04-03Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2348-1244

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