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7 May 2007

Volume 90, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 90, 193501 (2007); http://dx.doi.org/10.1063/1.2737344 (3 pages)

Peter Modregger, Daniel Lübbert, Peter Schäfer, and Rolf Köhler
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Ordered Ni nanohole arrays with engineered geometrical aspects and magnetic anisotropy

D. Navas, M. Hernández-Vélez, M. Vázquez, W. Lee, and K. Nielsch

Appl. Phys. Lett. 90, 192501 (2007); http://dx.doi.org/10.1063/1.2737373 (3 pages) | Cited 23 times

Online Publication Date: 7 May 2007

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Ni nanohole arrays are prepared by a replication process involving sputtering, polymer molding pressing, and electroplating techniques, using anodic alumina membranes as templates. Nanohole diameter to interhole distance ratio is engineered by suitable template processing. From the analysis of the magnetization curves for increasing nanohole diameter, it is concluded that coercivity increases due to the pinning of domain walls to nanoholes, while in-plane anisotropy decreases owing to local shape anisotropy effects.
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81.07.Bc Nanocrystalline materials
75.30.Gw Magnetic anisotropy
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Pq Electrodeposition, electroplating
75.60.Ch Domain walls and domain structure

Charge redistribution at YBa2Cu3O7-metal interfaces

U. Schwingenschlögl and C. Schuster

Appl. Phys. Lett. 90, 192502 (2007); http://dx.doi.org/10.1063/1.2737397 (3 pages) | Cited 20 times

Online Publication Date: 7 May 2007

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Charge redistribution at interfaces is crucial for electronic applications of high-Tc superconductors, since the band structure is modified on a local scale. The authors address the normal-state electronic structure of YBa2Cu3O7 (YBCO) at an YBCO-metal contact by first principles calculations for prototypical interface configurations. They derive quantitative results for the intrinsic doping of the superconducting CuO2 planes due to the metal contact. Their findings can be explained in terms of a band-bending mechanism, complemented by local screening effects. The authors determine a net charge transfer of 0.09–0.13 electrons in favor of the intraplane Cu sites, depending on the interface orientation.
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74.72.-h Cuprate superconductors
74.25.Jb Electronic structure (photoemission, etc.)
74.25.F- Transport properties

Probing momentum distributions in magnetic tunnel junctions via hot-electron decay

R. Jansen, T. Banerjee, B. G. Park, and J. C. Lodder

Appl. Phys. Lett. 90, 192503 (2007); http://dx.doi.org/10.1063/1.2737128 (3 pages)

Online Publication Date: 8 May 2007

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The tunnel momentum distribution in a (magnetic) tunnel junction is probed by analyzing the decay of the hot electrons in the Co metal anode after tunneling, using a three-terminal transistor structure in which the hot-electron attenuation is sensitive to the tunnel momentum distribution. Solid state amorphous Al2O3 barriers and the vacuum barrier of a scanning tunneling microscope are compared. For the former the attenuation length in nominally the same Co is strikingly larger (factor of 2), implying a more isotropic tunnel momentum distribution for Al2O3 barriers.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Tv Field effect devices

Absence of magnetic domain wall motion during magnetic field induced twin boundary motion in bulk magnetic shape memory alloys

Y. W. Lai, N. Scheerbaum, D. Hinz, O. Gutfleisch, R. Schäfer, L. Schultz, and J. McCord

Appl. Phys. Lett. 90, 192504 (2007); http://dx.doi.org/10.1063/1.2737934 (3 pages) | Cited 19 times

Online Publication Date: 8 May 2007

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A detailed study of twin boundary motion in NiMnGa single crystals together with in situ magnetic domain observation is presented. Optical polarization microscopy in connection with a magneto-optical indicator film technique was used to investigate the reorganization of the magnetic domains during twin boundary motion over a wide magnetic field range. Images at different field strengths demonstrate that no magnetic domain wall motion within the twins takes place, even during the structural reorientation by twin boundary movement. This absence of interaction of magnetic and structural domains is different from currently proposed models, which assume domain wall movement under an external field.
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75.60.Ch Domain walls and domain structure
61.72.Mm Grain and twin boundaries
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.20.Ls Magneto-optical effects

High-temperature ferromagnetism in amorphous semiconductor Ge3Mn thin films

Sung-Kyu Kim, Yong Chan Cho, Se-Young Jeong, Chae-Ryong Cho, Sang Eon Park, J. H. Lee, Jong-Pil Kim, Y. C. Kim, and H. W. Choi

Appl. Phys. Lett. 90, 192505 (2007); http://dx.doi.org/10.1063/1.2734174 (3 pages) | Cited 8 times

Online Publication Date: 10 May 2007

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The Ge1−xMnx thin films were fabricated at x = 0.25, of which the composition is close to Ge3Mn. They showed ferromagnetism up to above 350 K, even though their structure is amorphous. Ge3Mn amorphous samples grown at 200 °C have n-type characteristics, while those grown at 500 °C have p-type characteristics. The former has a different state from the latter, energetically. It is suggested that the different short range orders of Ge3Mn5 and/or Ge8Mn11 have already formed in the amorphous phase according to the growth temperature. The authors have also discussed the relationship between ferromagnetism and cluster formations after annealing at 800 °C.
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75.50.Pp Magnetic semiconductors
81.05.Gc Amorphous semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.Cc Kinetics of defect formation and annealing

Magnetic properties of postoxidized Pt/Co/Al layers with perpendicular anisotropy

D. Lacour, M. Hehn, M. Alnot, F. Montaigne, F. Greullet, G. Lengaigne, O. Lenoble, S. Robert, and A. Schuhl

Appl. Phys. Lett. 90, 192506 (2007); http://dx.doi.org/10.1063/1.2734378 (3 pages) | Cited 6 times

Online Publication Date: 10 May 2007

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The magnetic properties of ultrathin Co layers sandwiched between Pt and Al layers are studied as a function of the Al layer oxidation time. The association of three batches of complementary experiments (extraordinary Hall effect, x-ray photoelectron spectroscopy, and tunneling magnetoresistance) allows the authors to finely characterize their samples both magnetically and chemically. The authors show that their oxidation process reduces the coercive field of ultrathin Co layers with perpendicular anisotropy (case of short oxidation time) and can even induce transition from a ferromagnetic to a superparamagnetic state (lengthy oxidation time).
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Np Metals and alloys
81.65.Mq Oxidation

Analyses on the dispersion spectra of permeability and permittivity for NiZn spinel ferrites doped with SiO2

Mangui Han, Difei Liang, and Longjiang Deng

Appl. Phys. Lett. 90, 192507 (2007); http://dx.doi.org/10.1063/1.2722703 (3 pages) | Cited 13 times

Online Publication Date: 11 May 2007

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The permeability spectra of NiZn spinel ferrites with different amounts of SiO2 (0,0.3,0.5 wt %) aggregated at the grain boundaries have been resolved into two contribution components: domain wall resonance and spin rotation relaxation. The fitting results of permeability dispersion show that the spin rotation relaxation mechanism makes major contributions to the dispersion. With increasing the contents of SiO2, the fitting results of permittivity dispersion spectra show a wider distribution of relaxation time and a longer relaxation time.
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75.50.Gg Ferrimagnetics
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries
75.60.Ch Domain walls and domain structure

Electrical study of ferromagnet-oxide-semiconductor diode for a magnetic memory device integrated on silicon

M. Kanoun, R. Benabderrahmane, C. Duluard, C. Baraduc, N. Bruyant, A. Bsiesy, and H. Achard

Appl. Phys. Lett. 90, 192508 (2007); http://dx.doi.org/10.1063/1.2737823 (3 pages) | Cited 4 times

Online Publication Date: 11 May 2007

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This work focuses on electrical characterization of NiFe/SiO2/Si tunnel diodes that can be used for spin injection into silicon in future spintronic devices. Capacitance-voltage characteristics show a large increase of the Si/SiO2 interfacial state density compared to similar Al/SiO2/Si diodes. This result suggests that nickel and/or iron may have diffused across the SiO2 layer. Consistently the current-voltage experimental characteristics have been modeled by using trap assisted electron transport mechanism. These traps may be attributed to ferromagnet atoms in the oxide bulk.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
84.30.Sk Pulse and digital circuits
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
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