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30 Jun 2003

Volume 82, Issue 26, pp. 4633-4843

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4797 (2003); http://dx.doi.org/10.1063/1.1587262 (3 pages)

Ongi Englander, Dane Christensen, and Liwei Lin
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Self-assembly and magnetic properties of cobalt nanoparticles

H. T. Yang, C. M. Shen, Y. K. Su, T. Z. Yang, H. J. Gao, and Y. G. Wang

Appl. Phys. Lett. 82, 4729 (2003); http://dx.doi.org/10.1063/1.1586481 (3 pages) | Cited 35 times

Online Publication Date: 24 June 2003

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Two- and three-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. The size and stabilization of the cobalt nanoparticles are controlled by using the combination of oleic acid and triphenylphosphine. The cobalt nanoparticles are stable for at least 90 days without oxidation at room temperature under ambient conditions. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
81.16.Be Chemical synthesis methods
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Current-induced effect on the resistivity of epitaxial thin films of La0.7Ca0.3MnO3 and La0.85Ba0.15MnO3

J. Gao, S. Q. Shen, T. K. Li, and J. R. Sun

Appl. Phys. Lett. 82, 4732 (2003); http://dx.doi.org/10.1063/1.1587001 (3 pages) | Cited 67 times

Online Publication Date: 24 June 2003

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Electric-current-dependent resistance has been studied in epitaxial thin films of La0.7Ca0.3MnO3 and La0.85Ba0.15MnO3. Attention was focused at the influence of the applied dc current on the resistance of these epitaxial thin films in the absence of a magnetic field. A significant change in the ratio of the peak resistance at different currents or current resistance was found to be ∼23%–26% with a current density up to 8×104 Acm−2. For both La0.7Ca0.3MnO3 and La0.85Ba0.15MnO3 compounds, the dependence of the measured resistance on the current revealed a good linear relationship. Although the nature behind such an effect has not been well understood yet, the feature that the resistance in doped manganese oxides could be easily controlled by the electric current should be of interest for various applications such as field effect devices. © 2003 American Institute of Physics.
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73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films

Electron transport properties in magnetic tunnel junctions with epitaxial NiFe (111) ferromagnetic bottom electrodes

Ji Hyung Yu, Hyuck Mo Lee, Yasuo Ando, and Terunobu Miyazaki

Appl. Phys. Lett. 82, 4735 (2003); http://dx.doi.org/10.1063/1.1587271 (3 pages) | Cited 9 times

Online Publication Date: 24 June 2003

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By employing epitaxial NiFe (111) films as ferromagnetic bottom electrodes, magnetic tunnel junctions with layer sequence of Si (111)/epitaxial Ag/epitaxial Cu/epitaxial NiFe/Al-oxide/CoFe/IrMn/NiFe/Ta were prepared. High tunneling magnetoresistance (TMR) ratios were obtained and the bias dependence of TMR was remarkably reduced. The reason for the small bias dependence of TMR was explained by inelastic electron tunneling spectroscopy. It was clearly elucidated that a well-defined sharp interface formed between the tunnel barrier and the ferromagnetic electrode that is nearly free of crystalline defects. This magnetic tunnel junction has a large capability in engineering aspects if we can reduce the barrier thickness further by decreasing the interface roughness. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys

Investigation of superparamagnetism in Co–Zn ferrite thin films produced by pulsed-laser deposition

D. Ravinder and P. Shalini

Appl. Phys. Lett. 82, 4738 (2003); http://dx.doi.org/10.1063/1.1581980 (2 pages) | Cited 2 times

Online Publication Date: 24 June 2003

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Modern communication systems use increasingly higher frequencies and smaller and lighter possible devices. This requires magnetic devices using thin-film inductors or transformers and microwave integrated nonreciprocal circuits with incorporated thin ferrite films. Due to their better high-frequency characteristics, the polycrystalline materials are preferred to the monocrystalline ones in such thin-film applications. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Tt Fine-particle systems; nanocrystalline materials
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
81.15.Fg Pulsed laser ablation deposition

Theory of semiconductor magnetic bipolar transistors

M. E. Flatté, Z. G. Yu, E. Johnston-Halperin, and D. D. Awschalom

Appl. Phys. Lett. 82, 4740 (2003); http://dx.doi.org/10.1063/1.1586996 (3 pages) | Cited 49 times

Online Publication Date: 24 June 2003

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Bipolar transistors with a ferromagnetic base are shown theoretically to have the potential to generate almost 100% spin-polarized current injection into nonmagnetic semiconductors. Optical control of ferromagnetism and spin splitting in the base can lead to either long-lived or ultrafast switching behavior. Fringe field control of the base magnetization could be used for information transfer between metallic magnetoelectronics and conventional semiconducting electronics. © 2003 American Institute of Physics.
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85.30.Pq Bipolar transistors
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Decoupling between rare-earth moment and transition metal moment in NdCo12−xVx compounds

W. F. Liu, G. H. Rao, Z. W. Ouyang, H. F. Yang, G. Y. Liu, X. M. Feng, H. Chang, and J. K. Liang

Appl. Phys. Lett. 82, 4743 (2003); http://dx.doi.org/10.1063/1.1587884 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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Single-phase compounds NdCo12−xVx (x = 2.2–2.6) crystallizing in the tetragonal ThMn12 structure with space group I4/mmm are synthesized. The lattice parameters a and c increase linearly with increasing V content. The Curie temperature of the compounds shows a linear decrease from 309 K for x = 2.2 to 147 K for x = 2.6. A domain-wall pinning phenomenon is observed in all of the compounds. It is intriguing that the Nd ions seem to make no contribution to the total moment of the compounds in an applied magnetic field up to 50 kOe. A further increase of the applied field induces a moment of a Nd sublattice that ferromagnetically couples with the moment of a Co sublattice. The instability of the Nd moment in NdCo12−xVx compounds can be well understood by the local environment effect. © 2003 American Institute of Physics.
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75.30.Cr Saturation moments and magnetic susceptibilities
61.66.Dk Alloys
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
75.60.Ch Domain walls and domain structure

Magnetization steps in a noncharge-ordered manganite, Pr0.5Ba0.5MnO3

C. Autret, A. Maignan, C. Martin, M. Hervieu, V. Hardy, S. Hébert, and B. Raveau

Appl. Phys. Lett. 82, 4746 (2003); http://dx.doi.org/10.1063/1.1588756 (3 pages) | Cited 8 times

Online Publication Date: 24 June 2003

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Magnetization and resisitivity steps under application of a magnetic field are evidenced in absence of charge ordering at low temperature (T = 2.5 K), in the manganite Pr0.5Ba0.5MnO3. Electron microscopy observations emphasize the important role of phase separation, suggesting that the observed antiferromagnetic to ferromagnetic metamagnetic transition originates from cation-ordered PrBaMn2O6 nanoregions. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.50.Dd Nonmetallic ferromagnetic materials
64.75.-g Phase equilibria
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Observation of sphere resonance peak in ferromagnetic GaN:Mn

S. S. A. Seo, M. W. Kim, Y. S. Lee, T. W. Noh, Y. D. Park, G. T. Thaler, M. E. Overberg, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 82, 4749 (2003); http://dx.doi.org/10.1063/1.1588741 (3 pages) | Cited 28 times

Online Publication Date: 24 June 2003

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We report temperature-dependent optical spectra of ferromagnetic Mn-doped GaN in a wide photon energy region of 5 meV–4 eV. Below the GaN gap, an absorption peak around 1.25 eV whose intensity increases at lower temperatures was observed. A composite medium theory, called the Maxwell–Garnett theory, shows that the absorption peak can be assigned to a sphere resonance from metallic particles embedded in a Mn-doped GaN matrix. We also report that the far-infrared absorption of Mn-doped GaN sample was very small. This result suggests that itinerant carrier-mediated ferromagnetism does not fully explain the observed magnetic properties. © 2003 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials

Josephson effect in high-Tc La2−xSrxCuO4/La2−xSrxCuO4 ramp-edge junctions

H. Haibara and I. Iguchi

Appl. Phys. Lett. 82, 4752 (2003); http://dx.doi.org/10.1063/1.1589183 (3 pages) | Cited 1 time

Online Publication Date: 24 June 2003

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The observation of Josephson effect in high-Tc La2−xSrxCuO4/La2−xSrxCuO4 (LSCO/LSCO) ramp-edge junctions is reported. The LSCO/LSCO ramp-edge junctions are fabricated by pulsed laser deposition, Ar ion milling, and photolithography techniques adopting an interface-engineered process. The fabricated junctions have the maximum Josephson current Ic of a few hundred microamperes and clear Shapiro steps are observable under microwave irradiation. The modulation of Ic under an external magnetic field is also recognized. © 2003 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
81.15.Fg Pulsed laser ablation deposition

Enhanced carrier-mediated ferromagnetism in GaMnN by codoping of Mg

K. H. Kim, K. J. Lee, D. J. Kim, H. J. Kim, Y. E. Ihm, C. G. Kim, S. H. Yoo, and C. S. Kim

Appl. Phys. Lett. 82, 4755 (2003); http://dx.doi.org/10.1063/1.1586484 (3 pages) | Cited 23 times

Online Publication Date: 24 June 2003

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The effects of Mg codoping on the structural, electronic transport, and magnetic properties of GaMnN films are investigated. Mg was shown to compete with Mn for incorporation into the growing films at impingement, and to replace Mn. The partial replacement of Mn by Mg in GaMnN has resulted in an increase of conductivity of the region. The enhanced transport property due to the highly efficient dopant Mg resulted in a remarkable increase of the saturation magnetization, indicating an interaction between Mn and Mg for the carrier-mediated ferromagnetism. The increased carrier population by Mg codoping enabled a full mediation among the Mn atoms, and consequently, suppressed the paramagnetic rise in the temperature-dependent magnetization measurement. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
73.61.Ey III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.50.Dn Low-field transport and mobility; piezoresistance
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