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7 May 2013

Volume 113, Issue 17, Articles (17xxxx)

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J. Appl. Phys. 113, 174302 (2013); http://dx.doi.org/10.1063/1.4798262 (4 pages)

Yuichiro Kurokawa, Takehiko Hihara, and Ikuo Ichinose
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back to top Spin-Dependent Properties and Spin Manipulation for Spintronics

Room-temperature detection of spin accumulation in silicon across Schottky tunnel barriers using a metal–oxide–semiconductor field effect transistor structure (invited)

K. Hamaya, Y. Ando, K. Masaki, Y. Maeda, Y. Fujita, S. Yamada, K. Sawano, and M. Miyao

J. Appl. Phys. 113, 17C501 (2013); http://dx.doi.org/10.1063/1.4793501 (6 pages)

Online Publication Date: 26 February 2013

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Using a metal-oxide-semiconductor field effect transistor structure with a high-quality CoFe/n+-Si contact, we systematically study spin injection and spin accumulation in a nondegenerated Si channel with a doping density of ∼4.5 × 1015 cm−3 at room temperature. By applying the gate voltage (VG) to the channel, we obtain sufficient bias currents (IBias) for creating spin accumulation in the channel and observe clear spin-accumulation signals even at room temperature. Whereas the magnitude of the spin signals is enhanced by increasing IBias, it is reduced by increasing VG interestingly. These features can be understood within the framework of the conventional spin diffusion model. As a result, a room-temperature spin injection technique for the nondegenerated Si channel without using insulating tunnel barriers is established, which indicates a technological progress for Si-based spintronic applications with gate electrodes.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Gk Tunneling
61.72.uf Ge and Si
72.25.Mk Spin transport through interfaces

A graphene solution to conductivity mismatch: Spin injection from ferromagnetic metal/graphene tunnel contacts into silicon

O. M. J. van 't Erve, A. L. Friedman, E. Cobas, C. H. Li, A. T. Hanbicki, K. M. McCreary, J. T. Robinson, and B. T. Jonker

J. Appl. Phys. 113, 17C502 (2013); http://dx.doi.org/10.1063/1.4793712 (3 pages)

Online Publication Date: 28 February 2013

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Spin-injection into silicon from a ferromagnetic metal requires a solution to the conductivity mismatch. Oxide tunnel barriers such as MgO, Al2O3, or SiO2 are typically used to solve this problem, but often include defects and must be several monolayers thick to avoid pinholes. At these thicknesses, the overall tunnel-barrier becomes highly resistive, preventing these junctions to be used in devices based on local magnetoresistance. Besides providing a spin dependent interface resistance, these barriers also prevent metal ions from diffusing into silicon, which would severely compromise device performance. Here, we show that we can lower the junction resistance by 2–3 orders of magnitude when using a single layer of graphene as the tunnel barrier rather than SiO2 or Al2O3. Hanle measurements show that the spin lifetime is independent of the tunnel barrier material (graphene, Al2O3, SiO2), demonstrating that the lifetime measured is not dominated by some characteristics of the tunnel barrier. The graphene provides a highly uniform barrier, with well-controlled thickness and minimal defect and trapped charge density, while successfully circumventing the conductivity mismatch between a ferromagnetic metal and Si and preventing metal ion diffusion from the FM contact.
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72.25.-b Spin polarized transport
72.20.My Galvanomagnetic and other magnetotransport effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
68.18.-g Langmuir-Blodgett films on liquids
73.40.Gk Tunneling

Tuning the spin pumping characteristics in Ni81Fe19/CuNx bilayer films

Lichuan Jin, Huaiwu Zhang, Xiaoli Tang, and Zhiyong Zhong

J. Appl. Phys. 113, 17C503 (2013); http://dx.doi.org/10.1063/1.4794872 (3 pages)

Online Publication Date: 12 March 2013

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We demonstrate that the spin pumping effect can be effectively tuned with nitriding the nonmagnetic layer in ferromagnetic/nonmagnetic (FM/NM) bilayer system. Series of Ni81Fe19/CuNx bilayer films were prepared by magnetron sputtering with different nitrogen partial pressures from 0% to 20%. The static magnetic properties of the Ni81Fe19/CuNx bilayer films were studied by vibrating sample magnetometer and dynamic magnetic properties was studied using a coplanar waveguide vector-network-analyzer ferromagnetic resonance spectrometer with an in-plane configuration. The results reveal that the static magnetic properties are not noticeably changed with capping a nitrified copper layer. Both the linewidth and the Gilbert damping parameter are strongly influenced by the nitrogen partial pressure during the copper layer nitride process. The spin-mixing conductance of the NiFe/CuNx bilayer films was quantified from the peak-to-peak linewidth of ferromagnetic resonance spectra based on the model of the spin pumping.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Optical spin orientation in group-IV heterostructures

Alberto Ferrari, Federico Bottegoni, Stefano Cecchi, Giovanni Isella, and Franco Ciccacci

J. Appl. Phys. 113, 17C504 (2013); http://dx.doi.org/10.1063/1.4794874 (3 pages)

Online Publication Date: 13 March 2013

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We investigate the electron spin polarization upon photoemission from different Si1−xGex heterostructures by means of Mott polarimetry. We demonstrate the possibility to lower the vacuum energy level below the bottom of the conduction band at the Γ point of the Brillouin zone in compressively strained Si1−xGex alloys and we show that the optimization of the stoichiometry of group-IV heterostructures leads to a spin polarization of the electrons in the conduction band up to P = 72%±3%. Such a value is not only greater than those attainable in compressively strained pure Ge heterostructures, but it is also comparable to the typical electron spin polarization values of III-V semiconductor heterostructures.
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72.25.Dc Spin polarized transport in semiconductors
72.25.Mk Spin transport through interfaces
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
61.66.Bi Elemental solids
61.66.Dk Alloys

Ultrathin magnetic oxide EuO films on Si(001) using SiOx passivation—Controlled by hard x-ray photoemission spectroscopy

C. Caspers, S. Flade, M. Gorgoi, A. Gloskovskii, W. Drube, C. M. Schneider, and M. Müller

J. Appl. Phys. 113, 17C505 (2013); http://dx.doi.org/10.1063/1.4795010 (3 pages)

Online Publication Date: 13 March 2013

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We present the chemical and structural optimization of ultrathin magnetic oxide EuO films on silicon. By applying a controlled in situ passivation of the Si(001) surface with SiOx in the monolayer regime, metallic silicide contaminations at the interface can be effectively reduced down to a sub-monolayer coverage, as was carefully quantified by interface-sensitive hard x-ray photoemission spectroscopy. Heteroepitaxial growth of EuO on Si(001) is sustained for this ultrathin SiOx-passivation, and bulk-near magnetic properties are observed for the 4 nm-thin EuO films. Our successful combination of chemically and structurally optimized EuO/Si(001) heterostructures by ultrathin in situ SiOx passivation makes this system promising for an application as alternative spin functional tunnel contacts in spin-FETs.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Rv Passivation
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.aj Insulators

Spin interference in Rashba metal ring in a time-dependent magnetic field

Ji Chen, Mansoor Bin Abdul Jalil, and Seng Ghee Tan

J. Appl. Phys. 113, 17C506 (2013); http://dx.doi.org/10.1063/1.4799619 (3 pages)

Online Publication Date: 8 April 2013

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We investigate spin transport in a metal square ring with a strong Rashba spin orbit coupling (RSOC) effect, in the presence of a time-dependent magnetic field. We show that RSOC can be regarded as a spin-dependent gauge field which imparts a spin-dependent geometric phase (Aharonov-Casher phase) to conduction electrons in the ring. Combining the Aharonov-Bohm phase due to the time-dependent magnetic field with the able Aharonov-Casher phase due to RSOC, we are able to construct a spin interference condition, which modulates spin transport in the ring. The spin transport in the system is calculated via the tight-binding non-equilibrium Green's function formalism. Based on our transport calculations, we proposed a potential application of the Rashba square ring system as an alternating spin current generator.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.23.-b Electronic transport in mesoscopic systems

Detection of inverse spin Hall effect in epitaxial ferromagnetic Fe3Si films with normal metals Au and Pt

H. Y. Hung, G. Y. Luo, Y. C. Chiu, P. Chang, W. C. Lee, J. G. Lin, S. F. Lee, M. Hong, and J. Kwo

J. Appl. Phys. 113, 17C507 (2013); http://dx.doi.org/10.1063/1.4799147 (3 pages)

Online Publication Date: 9 April 2013

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Spin pumping transfers the spin momentum of the magnetization precession to the conduction electrons and forms pure spin currents, and was investigated in the ferromagnetic epitaxial Fe3Si films and polycrystalline Py films covered with normal metal (Pt, Au) overlayers, respectively. With the applied microwave applied from a cavity and an in-plane magnetic field, an electric voltage due to inverse spin-Hall effect is detected under the ferromagnetic resonance condition. A linear relationship between the measured voltage and microwave power has been obtained, consistent with a theoretical model. The spin Hall angles of Pt and Au as deduced from the present Py and Fe3Si data are in agreement with the published values. A very large voltage signal is observed for Fe3Si/Au film with in-situ capping of Au, suggesting the possibility of the future applications for the spintronic devices.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films
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