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12 Jun 2006

Volume 88, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 88, 243101 (2006); http://dx.doi.org/10.1063/1.2211007 (3 pages)

G. H. Du, F. Xu, Z. Y. Yuan, and G. Van Tendeloo
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Excitation and spin-transport of hot holes in ballistic hole magnetic microscopy

E. Haq, T. Banerjee, M. H. Siekman, J. C. Lodder, and R. Jansen

Appl. Phys. Lett. 88, 242501 (2006); http://dx.doi.org/10.1063/1.2212066 (3 pages) | Cited 1 time

Online Publication Date: 12 June 2006

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A hybrid structure of a ferromagnetic Co/Au/Ni81Fe19 trilayer on p-type silicon is used to probe the excitation of electron-hole pairs in a ferromagnet during inelastic decay of hot electrons and the subsequent spin-dependent transport of the excited holes into the valence band of the p-type Si collector. The hole current is remarkably sensitive to magnetic fields, with a magnetocurrent of up to 250% and, unexpectedly, with a positive sign. We determine effective attenuation lengths and their magnetic field and bias voltage dependence.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.25.Mk Spin transport through interfaces

Room-temperature ferromagnetism in (Mn, N)-codoped ZnO thin films prepared by reactive magnetron cosputtering

H. Y. Xu, Y. C. Liu, C. S. Xu, Y. X. Liu, C. L. Shao, and R. Mu

Appl. Phys. Lett. 88, 242502 (2006); http://dx.doi.org/10.1063/1.2213929 (3 pages) | Cited 38 times

Online Publication Date: 12 June 2006

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(Mn, N)-codoped ZnO films were grown on fused silica substrates by reactive magnetron cosputtering. X-ray diffraction measurements reveal that the films have the single-phase wurtzite structure with c-axis preferred orientation. X-ray photoelectron spectroscopy studies indicate the incorporation of both divalent Mn2+ and trivalent N3− ions into ZnO lattice. Acceptor doping with nitrogen partly compensates the “native donors,” which results in a low electron concentration of 3.16×1016 cm−3 though p-type conductivity is not achieved. (Mn, N)-codoped ZnO films show significant ferromagnetism with Curie temperature above 300 K. The mechanism of ferromagnetic coupling in codoped ZnO is discussed based on a bound magnetic polaron model.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Cd Deposition by sputtering

Effect of oxygen annealing on Mn doped ZnO diluted magnetic semiconductors

S. Ramachandran, J. Narayan, and J. T. Prater

Appl. Phys. Lett. 88, 242503 (2006); http://dx.doi.org/10.1063/1.2213930 (3 pages) | Cited 35 times

Online Publication Date: 12 June 2006

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We have investigated the properties of Zn1−xMnxO (x = 0.01–0.1) thin films grown on c-plane sapphire single crystals by pulsed laser deposition. The electrical, magnetic, optical, and microstructural properties of these thin films have been characterized systematically, with a primary focus on establishing a correlation between magnetic properties and electrical conductivity. We have shown that this system exhibits ferromagnetism at room temperature when in the conducting as-deposited state. However, upon high temperature annealing in excess oxygen, the samples become insulating and exhibit nonferromagnetic behavior at room temperature. Thus, it is possible to tune ferromagnetism in Zn1−xMnxO diluted magnetic semiconductors by controlling the concentrations of oxygen vacancies and substitutional Mn dopants.
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75.70.Ak Magnetic properties of monolayers and thin films
61.72.Cc Kinetics of defect formation and annealing
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters

Low field driven latching-type Bi3Fe5O12/Gd3Ga5O12 magneto-optical display

A. M. Grishin, S. I. Khartsev, and S. Bonetti

Appl. Phys. Lett. 88, 242504 (2006); http://dx.doi.org/10.1063/1.2213973 (3 pages) | Cited 6 times

Online Publication Date: 12 June 2006

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Series of heteroepitaxial all-garnet magneto-optical (MO) Bi3Fe5O12n/Gd3Ga5O12m (BIGn/GGGm, n = 1, 2, 3, 4, 5 and m = 1 and 2 are the numbers of unit cells) nanostructured multilayers have been sintered by pulsed laser deposition technique. Processing parameters and structure of grown films have been optimized to obtain perpendicular magnetic anisotropy and square hysteresis loop with low coercive and saturation magnetic fields. Regular alternating of lattice mismatched BIG and GGG atomic layers inhibited nucleation of misfit dislocations; thus a long range coherent compressive strain was preserved through the whole thickness of BIGn/GGGm multilayer stack. 2.5 μm thick BIG3/GGG2 sample (1200 BIG and 800 GGG unit cells) at λ = 678 nm shows MO Faraday rotation ΘF = ±1.4°, transmittance of 82%, attenuation α = 3400 dB/cm, squareness of magnetization loop (remnant-to-saturation magnetizations ratio) as high as 92%, and saturation and coercive fields as low as 56 and 25 Oe, respectively. MO remanence (latching capability) enables application of nanostructured garnet as a magnetic relief replicator/visualizer and as a material for low power consuming displays.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Magnetic/nonmagnetic/magnetic tunnel junction based on hybrid organic Langmuir-Blodgett-films

T. X. Wang, H. X. Wei, Z. M. Zeng, X. F. Han, Z. M. Hong, and G. Q. Shi

Appl. Phys. Lett. 88, 242505 (2006); http://dx.doi.org/10.1063/1.2213177 (3 pages) | Cited 21 times

Online Publication Date: 14 June 2006

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The magnetic/organic/magnetic spin valve structure has been fabricated with π-conjugated molecular pyrrole derivative 3-hexadecyl pyrrole as the spacer layer by Langmuir-Blodgett (LB) technique. It shows giant magnetoresistance (MR) as large as 20% at room temperature, demonstrating that low-energy electrons can traverse the molecular barrier while remaining spin polarized. The spin transport across organic structures is diffusive from its current-voltage (I-V) curve under bias voltage up to 1 V. The MR value decreased when the LB-film layer increased. The telegraph noise and the layer dependent MR value suggest that the spin-polarized transport signals can be degraded by localized states in the molecular barriers and barrier quality.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
72.25.Mk Spin transport through interfaces

AlN thin film as waveguide for shear acoustic waves

F. Martin and P. Muralt

Appl. Phys. Lett. 88, 242506 (2006); http://dx.doi.org/10.1063/1.2213510 (3 pages) | Cited 1 time

Online Publication Date: 14 June 2006

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A set of shear acoustic waves in the 78–195 MHz range composed of a surface skimming bulk wave and highly resolved shear acoustic plate modes has been simultaneously excited in a thin ST-cut quartz plate by means of transducers with a 1 μm thick sputtered AlN thin film used as a waveguiding layer. The effect of coating the transducers face with AlN is shown to increase the propagation speed of the first 13 plate modes in the ST-cut quartz, but then to decreases the propagation speed of plate modes higher than the 14th.
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43.20.Mv
43.35.Pt
43.35.Ns
68.60.Bs Mechanical and acoustical properties
68.35.Iv Acoustical properties
62.65.+k Acoustical properties of solids
43.58.Kr

Evidence of oxygen vacancy enhanced room-temperature ferromagnetism in Co-doped ZnO

H. S. Hsu, J. C. A. Huang, Y. H. Huang, Y. F. Liao, M. Z. Lin, C. H. Lee, J. F. Lee, S. F. Chen, L. Y. Lai, and C. P. Liu

Appl. Phys. Lett. 88, 242507 (2006); http://dx.doi.org/10.1063/1.2212277 (3 pages) | Cited 66 times

Online Publication Date: 16 June 2006

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The annealing effects on structure and magnetism for Co-doped ZnO films under air, Ar, and Ar/H2 atmospheres at 250 °C have been systematically investigated. Room-temperature ferromagnetism has been observed for the as-deposited and annealed films. However, the saturation magnetization (Ms) varied drastically for different annealing processes with Ms ∼ 0.5, 0.2, 0.9, and 1.5 μB/Co for the as-deposited, air-annealed, Ar-annealed, and Ar/H2-annealed films, respectively. The x-ray absorption spectra indicate all these samples show good diluted magnetic semiconductor structures. By comparison of the x-ray near edge spectra with the simulation on Zn K edge, an additional preedge peak appears due likely to the formation of oxygen vacancies. The results show that enhancement (suppression) of ferromagnetism is strongly correlated with the increase (decrease) of oxygen vacancies in ZnO. The upper limit of the oxygen vacancy density of the Ar/H2-annealed film can be estimated by simulation to be about 1×1021 cm−3.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Thermal limits on field alignment of nanoparticle FePt media

James A. Bain and William F. Egelhoff

Appl. Phys. Lett. 88, 242508 (2006); http://dx.doi.org/10.1063/1.2213515 (3 pages) | Cited 3 times

Online Publication Date: 16 June 2006

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We derive a simple expression for the average angular orientation distribution of ferromagnetic FePt particles in an applied field in thermal equilibrium. This system is closely related to the Langevin expression for paramagnetic susceptibility, which computes the average orientation of particles in this configuration. We note that practical fields are unlikely to be able to provide well-aligned arrays of the smallest thermally stable FePt particles at room temperature and that this has significant consequences for self-organized nanoparticle magnetic media. It suggests that it may be difficult to obtain an acceptable degree of perfection in orientation for the smallest particles.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.20.En Metals and alloys
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
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