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11 Sep 2006

Volume 89, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 89, 111104 (2006); http://dx.doi.org/10.1063/1.2353804 (3 pages)

Yi Yang and Guo Ping Wang
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Single crystal Fe films grown on Ge (001) substrates by magnetron sputtering

J. Lou, A. Daigle, L. Chen, Y. Q. Wu, V. G. Harris, C. Vittoria, and N. X. Sun

Appl. Phys. Lett. 89, 112501 (2006); http://dx.doi.org/10.1063/1.2339041 (3 pages) | Cited 2 times

Online Publication Date: 11 September 2006

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Single crystal Fe films were grown on Ge (001) substrates by using dc magnetron sputtering. It was found that the microstructures and magnetic properties of Fe films on Ge substrates were strongly dependent upon the substrate temperature during the deposition process. There existed a narrow substrate temperature window of 125±25 °C for achieving single crystal Fe film on Ge. Lower substrate temperature led to polycrystalline Fe films due to limited mobility of Fe atoms, while higher substrate temperatures resulted in amorphous Fe–Ge alloy due to severe interdiffusion.
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68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
66.30.Ny Chemical interdiffusion; diffusion barriers

Enhanced room temperature ferromagnetism in Co- and Mn-ion-implanted silicon

P. R. Bandaru, J. Park, J. S. Lee, Y. J. Tang, L.-H. Chen, S. Jin, S. A. Song, and J. R. O’Brien

Appl. Phys. Lett. 89, 112502 (2006); http://dx.doi.org/10.1063/1.2243802 (3 pages) | Cited 24 times

Online Publication Date: 11 September 2006

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The authors report on ferromagnetism at room temperature in cluster-free, cobalt- and manganese-ion-implanted crystalline silicon. Through magnetic and structural analysis it is shown that the ion-implanted Si consists of two layers of Co- and Mn-containing silicon: (1) an amorphous Si layer on the surface and (2) single crystalline Si beneath. The amorphous layer shows very little magnetism by itself but seems to be responsible for partially canceling out or masking the ferromagnetism in the crystalline Si. The authors also observe that etching of the amorphous Si layer dramatically enhances the measured magnetism by as much as 400%.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
61.72.uf Ge and Si
81.65.Cf Surface cleaning, etching, patterning

Interlayer exchange coupling in Fe/MgO/Fe magnetic tunnel junctions

T. Katayama, S. Yuasa, J. Velev, M. Ye. Zhuravlev, S. S. Jaswal, and E. Y. Tsymbal

Appl. Phys. Lett. 89, 112503 (2006); http://dx.doi.org/10.1063/1.2349321 (3 pages) | Cited 41 times

Online Publication Date: 12 September 2006

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Interlayer exchange coupling (IEC) in fully epitaxial Fe/MgO/Fe(001) tunnel junctions with wedge-shaped MgO layers is measured at room temperature from the unidirectional shift of the Kerr hysteresis loop. It is found that the IEC is antiferromagnetic for small MgO thickness but changes sign at 0.8 nm. Ab initio calculations of IEC show that this behavior can be explained by the presence of O vacancies in the MgO barrier which makes IEC antiferromagnetic for thin barriers. With increasing MgO thickness the resonance contribution to IEC from localized defect states is reduced resulting in the ferromagnetic coupling typical for perfect MgO barriers.
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75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
61.72.J- Point defects and defect clusters

Magnetic properties of epitaxial CrN films

A. Ney, R. Rajaram, S. S. P. Parkin, T. Kammermeier, and S. Dhar

Appl. Phys. Lett. 89, 112504 (2006); http://dx.doi.org/10.1063/1.2352795 (3 pages) | Cited 8 times

Online Publication Date: 12 September 2006

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The authors have investigated the structural and magnetic properties of CrN films grown on MgO(001) and sapphire(0001) by rf-plasma-assisted molecular beam epitaxy. CrN/MgO(001) exhibits a better epitaxial quality than CrN/sapphire(0001). The CrN/MgO film shows clear paramagnetic behavior at low temperatures, whereas CrN/sapphire exhibits a ferromagneticlike response with an order temperature above room temperature which resembles the magnetic behavior found in Cr-doped dilute magnetic semiconductors. Keeping in mind that bulk CrN exhibits antiferromagnetic behavior, the dramatically different magnetic behaviors found in epitaxial CrN films grown on MgO and sapphire demonstrate the importance of epitaxial constraints in determining their magnetic properties.
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75.70.Ak Magnetic properties of monolayers and thin films
75.20.Ck Nonmetals
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth

Observation of step-induced magnetic domain formation in La1−xSrxMnO3 thin films by photoelectron emission microscopy

T. Taniuchi, H. Kumigashira, M. Oshima, T. Wakita, T. Yokoya, M. Kubota, K. Ono, H. Akinaga, M. Lippmaa, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 89, 112505 (2006); http://dx.doi.org/10.1063/1.2347895 (3 pages) | Cited 14 times

Online Publication Date: 13 September 2006

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Magnetic domain formation in thin films of La1−xSrxMnO3 (LSMO) with x = 0.2 and 0.4 epitaxially grown on stepped SrTiO3 (001) substrates has been investigated by photoelectron emission microscopy. The magnetic domains show a stripe structure elongated along the step directions, indicating uniaxial magnetic anisotropy induced by step structures. We have also found that the magnetization of the magnetic domains is slightly meandering at domain boundaries. The existence of the additional structures suggests that the magnetic domains in LSMO films are also influenced by biaxial magnetocrystalline anisotropy. The direct observation of the magnetic domain structures suggests that the competition between the two magnetic anisotropies may play an important role in magnetic properties in LSMO films.
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75.60.Ch Domain walls and domain structure
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
79.60.Dp Adsorbed layers and thin films
78.20.Ls Magneto-optical effects

Perpendicular anisotropy in electrodeposited, Co-rich Co–Pt films by use of Ru underlayers

G. Pattanaik, G. Zangari, and J. Weston

Appl. Phys. Lett. 89, 112506 (2006); http://dx.doi.org/10.1063/1.2339070 (3 pages) | Cited 6 times

Online Publication Date: 13 September 2006

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Co-rich Co–Pt alloys were electrodeposited from an amino-citrate-based solution on a Si (011)/Cu(111)/Ru(0001) seed layer. Such a template provides an appropriate interface structure for the growth of a (0002)-oriented hexagonal phase, stabilized at larger thickness by the electrolyte chemistry, providing for a columnar structure with no detectable grain coarsening. This results in as-deposited Co–Pt films exhibiting perpendicular anisotropy (anisotropy constant up to 1.2 MJ/m3) and hard magnetic properties (coercivity up to 358.2 kA/m) in a wide thickness range, from 5 to 2000 nm. Crystalline, magnetoelastic, and interface effects are discussed as possible origins of the observed perpendicular anisotropy.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
68.55.-a Thin film structure and morphology
81.15.Pq Electrodeposition, electroplating
75.80.+q Magnetomechanical effects, magnetostriction

Paramagnetic anisotropy of Co-doped ZnO single crystal

Wei Li, Qingqing Kang, Zhang Lin, Wangsheng Chu, Dongliang Chen, Ziyu Wu, Yu Yan, Dagui Chen, and Feng Huang

Appl. Phys. Lett. 89, 112507 (2006); http://dx.doi.org/10.1063/1.2352726 (3 pages) | Cited 26 times

Online Publication Date: 13 September 2006

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Zn0.95Co0.05O single crystal was obtained through hydrothermal crystal growth method. Extended x-ray absorption fine structure and x-ray absorption near-edge structure spectra as well as UV absorption measurements reveal that Co2+ ions have substituted Zn2+ ions and incorporated into ZnO lattice. The single crystal shows typical paramagnetic property from 2 to 300 K. A paramagnetic anisotropy property in the crystal is found. The single ion anisotropy origin from tetrahedral coordination Co in the ZnO lattice was introduced to explain the phenomena. This work verified the paramagnetic anisotropy phenomena in ZnO–Co.
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81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
75.30.Gw Magnetic anisotropy
75.20.Ck Nonmetals
61.72.uj III-V and II-VI semiconductors
81.10.Dn Growth from solutions

Molecular enhancement of ferromagnetism in GaAs/GaMnAs heterostructures

Itai Carmeli, Francisco Bloom, E. G. Gwinn, T. C. Kreutz, Cheyne Scoby, A. C. Gossard, S. G. Ray, and Ron Naaman

Appl. Phys. Lett. 89, 112508 (2006); http://dx.doi.org/10.1063/1.2236935 (3 pages) | Cited 7 times

Online Publication Date: 14 September 2006

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The authors investigate effects of chemisorption of polar organic molecules onto ferromagnetic GaAs/GaMnAs heterostructures. The chemisorbed heterostructures exhibit striking anisotropic enhancement of the magnetization, while GaAs substrates that are physisorbed with the same molecules show no change in magnetic properties. Thus the enhanced magnetism of the chemisorbed heterostructures reflects changes in spin alignment that arise from surface bonding of the organic monolayer.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
68.43.Mn Adsorption kinetics
75.30.Gw Magnetic anisotropy
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetic gas sensing using a dilute magnetic semiconductor

A. Punnoose, K. M. Reddy, J. Hays, A. Thurber, and M. H. Engelhard

Appl. Phys. Lett. 89, 112509 (2006); http://dx.doi.org/10.1063/1.2349284 (3 pages) | Cited 12 times

Online Publication Date: 14 September 2006

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The authors report on a magnetic gas sensing methodology to detect hydrogen using the ferromagnetic properties of a nanoscale dilute magnetic semiconductor Sn0.95Fe0.05O2. This work demonstrates the systematic variation of saturation magnetization, coercivity, and remanence of Sn0.95Fe0.05O2 with the hydrogen gas flow rate, thus providing clear experimental evidence of the concept of magnetic gas sensing (using the magnetic property of a material as a gas sensing parameter). Based on the results of using hydrogen as an example for reducing gases, it is believed that any reducing gas capable of changing the oxygen stoichiometry of Sn0.95Fe0.05O2 can be detected using this method. Furthermore, this method presents an alternative gas sensing technology without the use of the electrical contacts.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Bi Elemental solids
61.66.Dk Alloys

Reading and writing of vortex circulation in pseudo-spin-valve ring devices

T. J. Hayward, J. Llandro, R. B. Balsod, J. A. C. Bland, F. J. Castaño, D. Morecroft, and C. A. Ross

Appl. Phys. Lett. 89, 112510 (2006); http://dx.doi.org/10.1063/1.2349305 (3 pages) | Cited 9 times

Online Publication Date: 14 September 2006

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The authors present a simple method of reading the circulation direction of vortex states in pseudo-spin-valve ferromagnetic ring devices via magnetoresistance measurements. It is shown that by placing the current contacts asymmetrically onto the structure, the circulation of a vortex state in the hard layer may be read directly from the total resistance of the device. Furthermore, they show that by choosing the direction in which the ring is initially saturated prior to obtaining the vortex state, the vortex circulation may be selectively written to the structure, creating the basis of a working memory element.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Spin injection from perpendicular magnetized ferromagnetic δ-MnGa into (Al,Ga)As heterostructures

C. Adelmann, J. L. Hilton, B. D. Schultz, S. McKernan, C. J. Palmstrøm, X. Lou, H.-S. Chiang, and P. A. Crowell

Appl. Phys. Lett. 89, 112511 (2006); http://dx.doi.org/10.1063/1.2349833 (3 pages) | Cited 15 times

Online Publication Date: 14 September 2006

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Electrical spin injection from ferromagnetic δ-MnGa into an (Al,Ga)As p-i-n light-emitting diode (LED) is demonstrated. The δ-MnGa layers show strong perpendicular magnetocrystalline anisotropy, enabling detection of spin injection at remanence, without an applied magnetic field. The bias and temperature dependence of the spin injection are found to be qualitatively similar to Fe-based spin LED devices. A Hanle effect is observed and demonstrates complete depolarization of spins in the semiconductor in a transverse magnetic field.
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72.25.Hg Electrical injection of spin polarized carriers
72.25.Mk Spin transport through interfaces
72.25.Ba Spin polarized transport in metals
72.25.Dc Spin polarized transport in semiconductors
75.50.Cc Other ferromagnetic metals and alloys
85.30.Kk Junction diodes

Rectification effects in superconducting triangles

M. Morelle, N. Schildermans, and V. V. Moshchalkov

Appl. Phys. Lett. 89, 112512 (2006); http://dx.doi.org/10.1063/1.2349834 (3 pages) | Cited 3 times

Online Publication Date: 14 September 2006

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A superconducting microtriangle is proposed to be used as a field-dependent diode. A dc voltage generated by the triangle induced by an applied ac drive is observed close to the superconducting/normal phase boundary. This effect is due to the superposition of the asymmetric screening currents in the triangle and the ac drive. The sign of the dc voltage is an alternating function of the applied magnetic field that reflects switching of the direction of the screening currents in the structure.
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85.25.Cp Josephson devices

Femtosecond laser source of nanolocalized directed photoelectrons

S. A. Aseyev, B. N. Mironov, S. V. Chekalin, and V. S. Letokhov

Appl. Phys. Lett. 89, 112513 (2006); http://dx.doi.org/10.1063/1.2353817 (2 pages) | Cited 3 times

Online Publication Date: 14 September 2006

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A nanolocalized electron beam has been formed by electrons passing through a quartz microcapillary. The authors have demonstrated that such electrons are capable of producing the image of a dielectric nanoaperture. Using the capillary and a metal tip illuminated by femtosecond laser pulses, the authors have developed a photoelectron source based on nanolocalized photoelectron bunches with low angular divergence. It allows the observation of femtosecond-laser-induced processes on a surface with high temporal and spatial resolutions.
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41.75.Fr Electron and positron beams
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Tunnel magnetoresistance for junctions with epitaxial full-Heusler Co2FeAl0.5Si0.5 electrodes with B2 and L21 structures

N. Tezuka, N. Ikeda, A. Miyazaki, S. Sugimoto, M. Kikuchi, and K. Inomata

Appl. Phys. Lett. 89, 112514 (2006); http://dx.doi.org/10.1063/1.2354026 (3 pages) | Cited 66 times

Online Publication Date: 14 September 2006

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The tunnel magnetoresistance (TMR) effect has been investigated for magnetic tunnel junctions with epitaxial Co2FeAl0.5Si0.5 Heusler electrodes with B2 and L21 structures on a Cr-bufferd MgO substrate. The epitaxially grown Co2FeAl0.5Si0.5 has B2 structure when annealed below 400 °C, and has L21 structure for annealing above 450 °C. The TMR ratio of 76% at room temperature and 106% at 5 K were obtained for a MgO(001)/Cr/B2-type Co2FeAl0.5Si0.5/Al oxide/Co75Fe25/IrMn/Ta. The TMR ratio is larger than that of magnetic tunnel junction with an L21-type electrode, which may be due to the smoother surface of the B2 structure and disordered L21 structure due to the Cr atom interdiffusion.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Np Metals and alloys
81.40.Gh Other heat and thermomechanical treatments
66.30.-h Diffusion in solids
68.55.A- Nucleation and growth

High Tc superconducting quantum interference devices made by ion irradiation

N. Bergeal, J. Lesueur, G. Faini, M. Aprili, and J. P. Contour

Appl. Phys. Lett. 89, 112515 (2006); http://dx.doi.org/10.1063/1.2348782 (3 pages) | Cited 12 times

Online Publication Date: 15 September 2006

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The authors describe a method to make superconducting quantum interference devices (SQUIDs) formed in a single layer of high Tc superconducting materials. The superconducting loop is patterned using ion beam irradiation through an in situ suitable gold mask. Josephson junctions are defined by a lower fluence irradiation through narrow slits opened in a polymethyl methacrylate resist. The critical current and the resistance of the SQUIDs at a given temperature can be adjusted precisely by choosing the fluence of irradiation to make the device operational at temperatures between 4.2 K and the Tc of the superconducting material.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.25.Cp Josephson devices
85.40.Hp Lithography, masks and pattern transfer

Spin reorientation transition in Fe-rich alloy films on W(110): The role of magnetoelastic anisotropy and structural transition

Hangil Lee, I.-G. Baek, and E. Vescovo

Appl. Phys. Lett. 89, 112516 (2006); http://dx.doi.org/10.1063/1.2354488 (3 pages) | Cited 4 times

Online Publication Date: 15 September 2006

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Epitaxial Fe-rich alloy films of formulas Fe1−xNix, Fe1−xCox, and Fe1−xVx were grown on a W(110) substrate with a bcc structure without any structural transition at x<0.3. Using chemical pressure (inserting small amounts of Ni, Co, or V into Fe), the authors controlled the lattice constant of these alloy films and then measured the variation of spin reorientation thickness (tr) according to the alloy composition. The authors focused on the roles of the lattice constant of the film and the spin reorientation thickness that is closely related to the strain associated with the lattice mismatch between the thin film and the substrate.
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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
68.55.-a Thin film structure and morphology
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
64.70.K- Solid-solid transitions

Magnetotransport properties of zinc-blende-structured MnAs films with half-metallic characteristics

Hee Chang Jeon, Tae Won Kang, Sh. U. Yuldashev, Tae Whan Kim, and Sungho Jin

Appl. Phys. Lett. 89, 112517 (2006); http://dx.doi.org/10.1063/1.2353823 (3 pages) | Cited 10 times

Online Publication Date: 15 September 2006

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Zinc-blende-structured MnAs epitaxial films were grown on GaAs (100) substrates with InAs buffer layer. The resistivity and the Hall resistance behavior at various temperatures indicate that the MnAs thin film is half-metallic in nature. A MnAs/GaAs/MnAs spin-valve structure, fabricated utilizing half-metallic MnAs thin films, exhibited giant magnetoresistance properties. The ability to fabricate epirelated half-metallic films on semiconductor surface can facilitate construction of many spin valves and related devices for potential spintronics and magnetic memory applications.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
75.47.De Giant magnetoresistance
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