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20 Aug 2012

Volume 101, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 101, 081102 (2012); http://dx.doi.org/10.1063/1.4745791 (3 pages)

M. K. Wu, M. Feng, and N. Holonyak, Jr.
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The origin of high surface spin-flip rate in metallic nonlocal spin valves

Han Zou and Yi Ji

Appl. Phys. Lett. 101, 082401 (2012); http://dx.doi.org/10.1063/1.4747215 (4 pages) | Cited 1 time

Online Publication Date: 20 August 2012

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The origin of high surface spin-flip rate in metallic nonlocal spin valves has been explored by tracking the evolution of the spin signals during the natural oxidation of the devices in air. The temperature dependence of spin signals evolves from a non-monotonic dependence with a maximum at ∼60 K for as-fabricated devices to a monotonic increase with decreasing temperatures for fully oxidized devices. The experimental results suggest that the high surface spin-flip rate originates from magnetic impurities near the side surfaces of the nonmagnetic channel and can be reduced by oxidation.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.65.Mq Oxidation
75.30.Hx Magnetic impurity interactions

Depinning of vortex domain walls from an asymmetric notch in a permalloy nanowire

Weiwei Zhu, Jialin Liao, Zongzhi Zhang, B. Ma, Q.Y Jin, Yaowen Liu, Zhaocong Huang, Xuefeng Hu, An Ding, Jing Wu, and Yongbing Xu

Appl. Phys. Lett. 101, 082402 (2012); http://dx.doi.org/10.1063/1.4745788 (4 pages)

Online Publication Date: 20 August 2012

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The mechanism of depinning process of vortex domain wall (DW) in a planar magnetic nanowire with an asymmetric notch is investigated by using focused magneto-optical Kerr effect (MOKE) magnetometer and micromagnetic modeling. Two distinct depinning fields are directly observed by the single-shot MOKE measurements. Micromagnetic modeling provides physical insight into the details of how the depinning process develops at the asymmetric notch and reveals that the different depinning fields originate from the different chiralities of the vortex DWs.
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75.75.-c Magnetic properties of nanostructures
75.78.Cd Micromagnetic simulations
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
78.20.Ls Magneto-optical effects

Efficient inducement of bistable spin Hall effect using in-plane-magnetized V-shaped ferromagnetic wire

T. Nomura, S. Nonoguchi, and T. Kimura

Appl. Phys. Lett. 101, 082403 (2012); http://dx.doi.org/10.1063/1.4747219 (4 pages) | Cited 1 time

Online Publication Date: 21 August 2012

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An advantageous device structure for the efficient electrical detection of spin Hall effect has been demonstrated by using a V-shaped ferromagnetic wire. The spin Hall voltages were evaluated by the combination between the spin absorption into the Platinum strip and the desired spin structure in the V-shaped Permalloy wire. Rectangular-shape field dependence of the spin Hall signal with bistability in the zero magnetic field reveals the validity of the developed device structure. We also showed that the domain wall chirality trapped at the corner of the V-shape wire can be determined from the sign of the spin Hall voltage.
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07.55.-w Magnetic instruments and components
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.25.Mk Spin transport through interfaces
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure

Spin transport and spin dephasing in zinc oxide

Matthias Althammer, Eva-Maria Karrer-Müller, Sebastian T. B. Goennenwein, Matthias Opel, and Rudolf Gross

Appl. Phys. Lett. 101, 082404 (2012); http://dx.doi.org/10.1063/1.4747321 (4 pages) | Cited 4 times

Online Publication Date: 21 August 2012

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The wide bandgap semiconductor ZnO is interesting for spintronic applications because of its small spin-orbit coupling implying a large spin coherence length. Utilizing vertical spin valve devices with ferromagnetic electrodes (TiN/Co/ZnO/Ni/Au), we study the spin-polarized transport across ZnO in all-electrical experiments. The measured magnetoresistance agrees well with the prediction of a two spin channel model with spin-dependent interface resistance. Fitting the data yields spin diffusion lengths of 10.8 nm (2 K), 10.7 nm (10 K), and 6.2 nm (200 K) in ZnO, corresponding to spin lifetimes of 2.6 ns (2 K), 2.0 ns (10 K), and 31 ps (200 K).
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72.25.Dc Spin polarized transport in semiconductors
72.25.Mk Spin transport through interfaces
72.80.Ey III-V and II-VI semiconductors
75.47.Pq Other materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.My Galvanomagnetic and other magnetotransport effects

Growth and ferromagnetic resonance of yttrium iron garnet thin films on metals

Yiyan Sun, Young-Yeal Song, and Mingzhong Wu

Appl. Phys. Lett. 101, 082405 (2012); http://dx.doi.org/10.1063/1.4747465 (3 pages)

Online Publication Date: 21 August 2012

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High-quality yttrium iron garnet (YIG) thin films were grown on a sandwich structure that consisted of a thick Cu layer and two thin cladding layers. The cladding layers were high entropy alloy nitrides (HEAN) and served as barriers to prevent Cu diffusion and oxidation during the YIG deposition. The Cu and HEAN layers were deposited by sputtering. The YIG films were grown by pulsed laser deposition. The YIG films had a thickness of several hundreds of nanometers, a surface roughness of several nanometers, and (111) orientation. The films showed a peak-to-peak ferromagnetic resonance linewidth of 1.1 Oe at 9.45 GHz.
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81.15.Fg Pulsed laser ablation deposition
75.50.Gg Ferrimagnetics
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Piezoelectric strain induced variation of the magnetic anisotropy in a high Curie temperature (Ga,Mn)As sample

A. Casiraghi, A. W. Rushforth, J. Zemen, J. A. Haigh, M. Wang, K. W. Edmonds, R. P. Campion, and B. L. Gallagher

Appl. Phys. Lett. 101, 082406 (2012); http://dx.doi.org/10.1063/1.4746250 (3 pages)

Online Publication Date: 21 August 2012

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We show that effective electrical control of the magnetic properties in the ferromagnetic semiconductor (Ga,Mn)As is possible using the strain induced by a piezoelectric actuator even in the limit of high doping levels and high Curie temperatures, where direct electric gating is not possible. We demonstrate very large and reversible rotations of the magnetic easy axis. We compare the results obtained from magneto-transport and superconducting quantum interference device magnetometry measurements, extracting the dependence of the piezo-induced uniaxial magnetic anisotropy constant upon strain in both cases and detailing the limitations encountered in the latter approach.
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75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order

Nonmagnetic spin-field-effect transistor

Jun-Feng Liu, K. S. Chan, and Jun Wang

Appl. Phys. Lett. 101, 082407 (2012); http://dx.doi.org/10.1063/1.4747494 (5 pages) | Cited 1 time

Online Publication Date: 22 August 2012

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We propose a spin-field-effect transistor based on a semiconductor quantum wire with spin-orbit coupling and normal electrical contacts, instead of the ferromagnetic contacts required in the Datta and Das spin-field-effect transistor. The spin of electrons can be completely polarized and detected by manipulating and detecting the orbital wave-function using the spin-orbit coupling. The central spin-orbit coupled region consists of two segments with different strengths of Rashba spin-orbit coupling α1 and α2, respectively. The conductance is nearly 1 for the case of α2 = α1 and 0 for α2 = −α1 in a wide energy range. The device can work as a nonmagnetic spin transistor, which can have important applications in spintronics.
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85.75.Hh Spin polarized field effect transistors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
85.30.Tv Field effect devices

Observation of magnetism, low resistivity, and magnetoresistance in the near-surface region of Gd implanted ZnO

P. P. Murmu, J. Kennedy, G. V. M. Williams, B. J. Ruck, S. Granville, and S. V. Chong

Appl. Phys. Lett. 101, 082408 (2012); http://dx.doi.org/10.1063/1.4747525 (4 pages)

Online Publication Date: 22 August 2012

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Ferromagnetic order is observed in Gd ion implanted ZnO crystals after annealing at 650 °C in a vacuum and we find that it is intrinsic and extends to depths of up to 40 nm. The ferromagnetic order is not affected by Gd for concentrations as high as 5% and possibly arises from defect clusters. Magnetoresistance is observed at low temperatures that may be due to spin-tunnelling between the defect clusters or spin-dependent scattering at the defect cluster interfaces. Gd implantation has an advantageous effect where it results in mΩ cm resistivities as well as significant electron doping.
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75.50.Pp Magnetic semiconductors
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials

Spin dependent recombination based magnetic resonance spectroscopy of bismuth donor spins in silicon at low magnetic fields

P. A. Mortemousque, T. Sekiguchi, C. Culan, M. P. Vlasenko, R. G. Elliman, L. S. Vlasenko, and K. M. Itoh

Appl. Phys. Lett. 101, 082409 (2012); http://dx.doi.org/10.1063/1.4747723 (4 pages) | Cited 1 time

Online Publication Date: 22 August 2012

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Low-field (6–110 mT) magnetic resonance of bismuth (Bi) donors in silicon has been observed by monitoring the change in photoconductivity induced by spin dependent recombination. The spectra at various resonance frequencies show signal intensity distributions drastically different from that observed in conventional electron paramagnetic resonance, attributed to different recombination rates for the forty possible combinations of spin states of a pair of a Bi donor and a paramagnetic recombination center. An excellent tunability of Bi excitation energy for the future coupling with superconducting flux qubits at low fields has been demonstrated.
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76.30.Lh Other ions and impurities
72.40.+w Photoconduction and photovoltaic effects
61.72.uf Ge and Si
71.35.-y Excitons and related phenomena

Electron spin resonance shift and linewidth broadening of nitrogen-vacancy centers in diamond as a function of electron irradiation dose

Edwin Kim, Victor M. Acosta, Erik Bauch, Dmitry Budker, and Philip R. Hemmer

Appl. Phys. Lett. 101, 082410 (2012); http://dx.doi.org/10.1063/1.4747211 (5 pages) | Cited 1 time

Online Publication Date: 23 August 2012

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A high-nitrogen-concentration diamond sample was subjected to 200-keV electron irradiation using a transmission electron microscope. The optical and spin-resonance properties of the nitrogen-vacancy (NV) color centers were investigated as a function of the irradiation dose up to 6.4 × 1021 e−/cm2. The microwave transition frequency of the NV− center was found to shift by up to 0.6% (17.1 MHz) and the linewidth broadened with increasing electron-irradiation dose. Unexpectedly, the measured magnetic sensitivity is best at the lowest irradiation dose, even though the NV concentration increases monotonically with increasing dose. This is in large part due to a sharp reduction in optically detected spin contrast at higher doses.
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76.30.Mi Color centers and other defects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.jd Vacancies
61.72.jn Color centers
61.80.Fe Electron and positron radiation effects
61.82.Ms Insulators

Electronic structure of room-temperature ferromagnetic Mg1−xFexOy thin films

Mukes Kapilashrami, Hui Zhang, Mei Fang, Xin Li, Xuhui Sun, K. V. Rao, Lyubov Belova, Yi Luo, and Jinghua Guo

Appl. Phys. Lett. 101, 082411 (2012); http://dx.doi.org/10.1063/1.4747445 (5 pages) | Cited 1 time

Online Publication Date: 23 August 2012

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We present herein a soft x-ray spectroscopy study on the electronic and magnetic properties of Mg1−xFexOy thin films. A distinct shoulder feature on the absorption edge reflecting the unoccupied oxygen 2p states is evident in the intrinsic thin films, which diminishes upon Fe doping, while a pre-edge absorption feature (reflecting the O 2p-Fe 3d acceptor state) evolves with the same. Our findings demonstrate the reduction in the intrinsic holes as a result of charge-transfer hole doping. All the thin films display room-temperature ferromagnetism, and the saturation magnetization is found to increase from ca. 0.70 → 4.34 emu/cm3 on 7 at. % Fe doping.
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71.20.Ps Other inorganic compounds
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
78.40.Ha Other nonmetallic inorganics
78.66.Nk Insulators

Depth-dependent magnetization reversal and spin structure of Fe/NiO exchange-coupled epitaxial bilayers

P. Luches, L. Pasquini, S. Benedetti, S. Valeri, R. Rüffer, and F. Boscherini

Appl. Phys. Lett. 101, 082412 (2012); http://dx.doi.org/10.1063/1.4747722 (4 pages)

Online Publication Date: 23 August 2012

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We investigate the depth-dependent magnetization reversal and spin structure of Fe/NiO epitaxial bilayers before and after field cooling. Using nuclear resonant scattering of synchrotron radiation we selectively probe the spin structure of the interfacial layers in contact with NiO. We provide a direct evidence that magnetization reversal involves a rotation in the film plane perpendicular to the applied field, except for the interfacial Fe layers. Moreover, we show that the spin structure of the ferromagnetic layer is not modified by field cooling and that the exchange bias in the Fe layer is independent of the distance from the antiferromagnetic phase.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.30.Sg Magnetocaloric effect, magnetic cooling

Engineering shallow spins in diamond with nitrogen delta-doping

Kenichi Ohno, F. Joseph Heremans, Lee C. Bassett, Bryan A. Myers, David M. Toyli, Ania C. Bleszynski Jayich, Christopher J. Palmstrøm, and David D. Awschalom

Appl. Phys. Lett. 101, 082413 (2012); http://dx.doi.org/10.1063/1.4748280 (5 pages) | Cited 14 times

Online Publication Date: 24 August 2012

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We demonstrate nanometer-precision depth control of nitrogen-vacancy (NV) center creation near the surface of synthetic diamond using an in situ nitrogen delta-doping technique during plasma-enhanced chemical vapor deposition. Despite their proximity to the surface, doped NV centers with depths (d) ranging from 5 to 100 nm display long spin coherence times, T2 > 100 μs at d = 5 nm and T2 > 600 μs at d ≥ 50 nm. The consistently long spin coherence observed in such shallow NV centers enables applications such as atomic-scale external spin sensing and hybrid quantum architectures.
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61.72.jd Vacancies
61.72.up Other materials
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Exchange-bias like hysteretic magnetoelectric-coupling of as-grown synthetic antiferromagnetic structures

Syed Rizwan, S. Zhang, Y. G. Zhao, and X. F. Han

Appl. Phys. Lett. 101, 082414 (2012); http://dx.doi.org/10.1063/1.4748304 (3 pages) | Cited 5 times

Online Publication Date: 24 August 2012

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Show Abstract
The magnetoelectric (ME) coupling of CoFeB/Ru/CoFeB synthetic antiferromagnetic (SAF) structure is studied at room-temperature when the SAF structure was deposited on the (011)-Pb(Mg1/3Nb2/3)O3-PbTiO3 piezoelectric substrate. It was found that the magnetoelectric coupling showed butterfly like curve when measured in the absence of magnetic field but it showed hysteresis loop-like behavior as well as the exchange-bias like shift of the ME hysteresis under fixed magnetic fields of +250 Oe and +500 Oe. This exchange-bias like hysteretic ME coupling is attributed to the direct coupling of CoFeB layer with the substrate ferroelectric domain, the absence of magnetocrystalline anisotropy and the switching of 109° ferroelastic domains of the substrate. We have also measured the magnetoelectric coupling of CoFe/Ru/CoFe SAF structure but observed no exchange-bias like hysteresis behavior. Our results establish another way of obtaining the non-volatile memory devices based on magnetoelectric systems.
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75.85.+t Magnetoelectric effects, multiferroics
75.50.Ee Antiferromagnetics
77.80.Dj Domain structure; hysteresis
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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