| 1. |
- Borschel, Christian, et al.
(författare)
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A New Route toward Semiconductor Nanospintronics : Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions
- 2011
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Ingår i: Nano letters (Print). - Washington : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 11:9, s. 3935-3940
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Kumar, Sandeep, et al.
(författare)
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Magnetic polarons and large negative magnetoresistance in GaAs nanowires implanted with Mn ions
- 2013
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Ingår i: Nano letters (Print). - Washington, United States : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 13:11, s. 5079-5084
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Tidskriftsartikel (refereegranskat)abstract
- 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 remarkably 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 forming a paramagnetic/spin-glass phase.
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| 3. |
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| 4. |
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| 5. |
- Liu, Ruisheng S., et al.
(författare)
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Magnetoresistance studies on CoAl OX Au and CoAl OX NiAu tunnel structures
- 2008
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Ingår i: Applied Physics Letters. - New York : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 93:20, s. 203107-203107-3
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Tidskriftsartikel (refereegranskat)abstract
- We report on magnetoresistance (MR) studies on CoAl OX Au and CoAl OX NiAu magnetic tunnel junctions. In spite of the fact that the difference between the two samples is merely a 3 nm thick Ni layer, there is a sharp contrast in MR behavior indicating that the electronic structure at the interface between the ferromagnetic electrodes and the insulating barrier dominates the MR signal. The former sample exhibits a clear tunneling anisotropic MR (TAMR), with the characteristic correlation between resistance and current direction, in contrast to the latter sample which displays a conventional tunneling MR (TMR) dominated by the relative orientation between the magnetization directions of the two electrodes. In addition, the TAMR has a much stronger temperature dependence than the TMR, indicating a much faster drop-off of the tunneling density of states anisotropy than the tunneling electron spin polarization with increasing temperature. Finally, we propose a possible simple way to distinguish TAMR from normal TMR by measuring the resistance of the device at different angles of the external magnetic field. 2008 American Institute of Physics.
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| 6. |
- Liu, Ruisheng, et al.
(författare)
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Tunneling anisotropic magnetoresistance in Co/AlOx/Au tunnel junctions
- 2008
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Ingår i: Nano letters (Print). - Washington : American Chemical Society. - 1530-6984 .- 1530-6992. ; 8:3, s. 848-852
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Tidskriftsartikel (refereegranskat)abstract
- We observe spin-valve-like effects in nanoscaled thermally evaporated Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and depends on the relative orientation of the magnetization direction of the Co electrode with respect to the current direction. We attribute this effect to a two-step magnetization reversal and an anisotropic density of states resulting from spin-orbit interaction. The results of this study points to future applications of novel spintronics devices involving only one ferromagnetic layer.
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| 7. |
- Paschoal Jr., Waldomiro, et al.
(författare)
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Hopping Conduction in Mn Ion-Implanted GaAs Nanowires
- 2012
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Ingår i: Nano letters (Print). - Washington : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 12:9, s. 4838-4842
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Tidskriftsartikel (refereegranskat)abstract
- We report on temperature-dependent charge transport in heavily doped Mn+-implanted GaAs nanowires. The results clearly demonstrate that the transport is governed by temperature-dependent hopping processes, with a crossover between nearest neighbor hopping and Mott variable range hopping at about 180 K. From detailed analysis, we have extracted characteristic hopping energies and corresponding hopping lengths. At low temperatures, a strongly nonlinear conductivity is observed which reflects a modified hopping process driven by the high electric field at large bias.
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| 8. |
- Paschoal Jr., Waldomiro, 1977-, et al.
(författare)
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Magnetoresistance in Mn ion-implanted GaAs:Zn nanowires
- 2014
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Ingår i: Applied Physics Letters. - New York : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 104:15
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Wu, Phillip M., et al.
(författare)
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Thermoelectric Characterization of Electronic Properties of GaMnAs Nanowires
- 2012
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Ingår i: Journal of Nanotechnology. - New York : Hindawi Publishing Corporation. - 1687-9503 .- 1687-9511. ; 2012
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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