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24 May 2004

Volume 84, Issue 21, pp. 4141-4340

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Appl. Phys. Lett. 84, 4316 (2004); http://dx.doi.org/10.1063/1.1756684 (3 pages)

Seok Pil Jang and Stephen U. S. Choi
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First-principles study of magnetism in (11math0) Zn1−xMnxO thin film

Q. Wang and P. Jena

Appl. Phys. Lett. 84, 4170 (2004); http://dx.doi.org/10.1063/1.1755834 (3 pages) | Cited 24 times

Online Publication Date: 6 May 2004

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First-principles calculations of total energies and magnetism of Zn1−xMnxO thin film are performed by simulating it with a slab consisting of seven layers along (11math0). It is shown that a single Mn atom shows very little preference for the site it occupies. This is consistent with the experimental finding that Mn atoms are homogeneously distributed in ZnO films. As the concentration of Mn atoms increases, antiferromagnetic coupling between Mn atoms becomes more favorable, and there is a tendency for Mn atoms to form clusters around oxygen, in agreement with recent experiments. © 2004 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors

Observation of photoluminescence emission in ferromagnetic semiconductor GaCrN

M. Hashimoto, H. Tanaka, R. Asano, S. Hasegawa, and H. Asahi

Appl. Phys. Lett. 84, 4191 (2004); http://dx.doi.org/10.1063/1.1756678 (3 pages) | Cited 11 times

Online Publication Date: 6 May 2004

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Optical properties of GaN-based diluted magnetic semiconductor GaCrN were studied. The GaCrN layers were grown by electron-cyclotron-resonance plasma-assisted molecular-beam epitaxy. They exhibited ferromagnetic behavior at room temperature and strong photoluminescence (PL) emission at 3.29 eV (10 K). The PL emission peak energy of the GaCrN decreases with increasing temperature in accordance with the Varshini formula similar to the GaN excitonic transition peak. The 3.29 eV PL emission was assigned to be a band-to-band transition in GaCrN from the temperature- and the excitation-power-density dependences of the PL. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
78.55.Cr III-V semiconductors
75.50.Cc Other ferromagnetic metals and alloys

Doping effects on the valence band of Tl2Mn2O7 pyrochlores: Relation to magnetoresistance

J. Sánchez-Benítez, A. de Andrés, C. Prieto, J. Ávila, L. Martín-Carrón, J. L. Martínez, J. A. Alonso, M. J. Martínez-Lope, and M. T. Casais

Appl. Phys. Lett. 84, 4209 (2004); http://dx.doi.org/10.1063/1.1755413 (3 pages) | Cited 2 times

Online Publication Date: 7 May 2004

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Photoemission and x-ray absorption near edge spectroscopy measurements have been performed in Tl2Mn2O7 oxides doped with 10% different ions, Bi, Cd, or Sb, which produce colossal changes in the magnetoresistance values. The contributions to the valence band related to Mn, O, and the doping ions have been obtained. We found that the paramagnetic phase of doped Tl pyrochlores is charge-transfer insulator type with oxygen character of the upper edge of the valence band. Bi 6s and Cd 4d orbitals lie also at the upper edge of the valence band. Mn valence is identical for all samples while oxygen content varies to compensate for the charge introduced by doping. The density of carriers, which is correlated to the magnetoresistance values, is determined by the density of states near the Fermi level provided by Tl and O content. © 2004 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
71.20.Ps Other inorganic compounds
61.72.up Other materials

Coercivity enhancements by high-magnetic-field annealing in sintered Nd–Fe–B magnets

Hiroaki Kato, Terunobu Miyazaki, Masato Sagawa, and Keiichi Koyama

Appl. Phys. Lett. 84, 4230 (2004); http://dx.doi.org/10.1063/1.1756193 (3 pages) | Cited 12 times

Online Publication Date: 7 May 2004

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An influence of a high-field annealing on the magnetic properties was investigated in sintered Nd–Fe–B magnets. When the sample B, containing 0.32 at. % Al, was annealed at Ta = 550 °C under a magnetic field of Ha = 140 kOe and then cooled without field, the coercivity Hc increased by 25% with respect to the control sample annealed at zero field. As for the sample C, containing both Cu 0.13 at. % and Al 0.32 at. %, higher Hc values were obtained when it was annealed at Ta = 550 °C and the field of Ha = 140 kOe was kept applied down to the room temperature. These results were discussed in terms of a field-induced change in interface matching between Nd2Fe14B and intergranular phases. © 2004 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys

Anomalous magnetic properties and Hall effect in ferromagnetic Co2MnAl epilayers

Y. J. Chen, D. Basiaga, J. R. O’Brien, and D. Heiman

Appl. Phys. Lett. 84, 4301 (2004); http://dx.doi.org/10.1063/1.1755842 (3 pages) | Cited 9 times

Online Publication Date: 7 May 2004

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Epitaxial films of the full Heusler alloy Co2MnAl were grown on GaAs substrates by molecular-beam epitaxy. The close lattice matching and similar structure to GaAs make this material a good candidate for a spin injector. Magnetization measurements reveal complex ferromagnetic transitions near the Curie point at TC ≃ 800 K. At room temperature, magnetotransport studies show metallic behavior and a giant Hall effect driven by the extraordinary Hall effect. © 2004 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Np Metals and alloys

Comparison of Fe/Schottky and Fe/Al2O3 tunnel barrier contacts for electrical spin injection into GaAs

O. M. J. van ’t Erve, G. Kioseoglou, A. T. Hanbicki, C. H. Li, B. T. Jonker, R. Mallory, M. Yasar, and A. Petrou

Appl. Phys. Lett. 84, 4334 (2004); http://dx.doi.org/10.1063/1.1758305 (3 pages) | Cited 67 times

Online Publication Date: 7 May 2004

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We compare electrical spin injection from Fe films into identical GaAs-based light-emitting diodes (LEDs) using different tunnel barriers—a reverse-biased Fe/AlGaAs Schottky contact and an Fe/Al2O3 barrier. Both types of structures are formed in situ using a multichamber molecular-beam epitaxy system. A detailed analysis of the transport data confirms that tunneling occurs in each case. We find that the spin polarization achieved in the GaAs using the Al2O3 barrier is 40% (best case; 30% typical), but the electrical efficiency is significantly lower than that of the Fe Schottky contact. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
72.25.Dc Spin polarized transport in semiconductors
72.25.Hg Electrical injection of spin polarized carriers
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