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21 Jun 2010

Volume 96, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 96, 251901 (2010); http://dx.doi.org/10.1063/1.3455157 (3 pages)

Yongsam Kim, Ankit S. Disa, Timur E. Babakol, and Joel D. Brock
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Gilbert magnetic damping constant of epitaxially grown Co-based Heusler alloy thin films

M. Oogane, T. Kubota, Y. Kota, S. Mizukami, H. Naganuma, A. Sakuma, and Y. Ando

Appl. Phys. Lett. 96, 252501 (2010); http://dx.doi.org/10.1063/1.3456378 (3 pages) | Cited 12 times

Online Publication Date: 21 June 2010

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The magnetic damping constant in a series of Co2MnAlxSi1−x and Co2FexMn1−xSi Heusler alloy epitaxial films were systematically investigated by using ferromagnetic resonance technique. The determined magnetic damping constant is roughly proportional to the density of states at the Fermi energy of the first principle calculation. The result is consistent with the theoretical prediction when taking spin-orbit interaction into account. The small Gilbert damping constant for the fabricated films other than the Co2FexMn1−xSi film with x>0.6 can be originated in the half-metallic electronic structure of Heusler alloys.
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71.15.-m Methods of electronic structure calculations
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.20.Gj Other metals and alloys
73.20.At Surface states, band structure, electron density of states
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
68.55.A- Nucleation and growth

Surface- and bulk-sensitive x-ray absorption study of the valence states of Mn and Co ions in Zn1−2xMnxCoxO nanoparticles

T. Kataoka, Y. Yamazaki, Y. Sakamoto, A. Fujimori, F.-H. Chang, H.-J. Lin, D. J. Huang, C. T. Chen, A. Tanaka, S. K. Mandal, T. K. Nath, D. Karmakar, and I. Dasgupta

Appl. Phys. Lett. 96, 252502 (2010); http://dx.doi.org/10.1063/1.3449556 (3 pages) | Cited 7 times

Online Publication Date: 22 June 2010

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We have performed x-ray absorption spectroscopy (XAS) measurements on Zn1−2xMnxCoxO nanoparticles. From the XAS results, it seems that the Mn and Co ions are in a mixed-valence (2+, 3+, and 4+) state and the relative concentrations of the high-valence (3+ and 4+) Mn and Co ions are higher in the surface region than in the deep core region. We suggest that this is a distinct trend of nanoparticle diluted magnetic semiconductor (DMS) unlike the case of DMS in film and bulk forms, where the transition-metal ions are expected to be 2+.
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75.50.Pp Magnetic semiconductors
78.70.Dm X-ray absorption spectra
75.50.Tt Fine-particle systems; nanocrystalline materials
73.22.-f Electronic structure of nanoscale materials and related systems

Magnetic susceptibility measurements as a probe of spin transfer driven magnetization dynamics

Weiwei Lin (林维维), J. Cucchiara, C. Berthelot, T. Hauet, Y. Henry, J. A. Katine, Eric E. Fullerton, and S. Mangin

Appl. Phys. Lett. 96, 252503 (2010); http://dx.doi.org/10.1063/1.3454782 (3 pages) | Cited 2 times

Online Publication Date: 23 June 2010

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An experimental technique has been developed to characterize spin-transfer driven magnetization dynamics. It was tested on a nanopillar spin valve with perpendicular anisotropy by measuring the nanopillar voltage under ac injected current (dV/dI), and ac magnetic field (dV/dH). Both the amplitude and the sign of the signals are different which reveals the different influences of the current and the field on the magnetization dynamics. Comparison between experiments and macrospin simulation shows that dV/dH measurements reveal the presence of a “canted state” demonstrating that dV/dH and dV/dI measurements are complementary techniques to probe magnetic states and their dynamics.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.75.-c Magnetic properties of nanostructures
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Observation of full shot noise in CoFeB/MgO/CoFeB-based magnetic tunneling junctions

K. Sekiguchi, T. Arakawa, Y. Yamauchi, K. Chida, M. Yamada, H. Takahashi, D. Chiba, K. Kobayashi, and T. Ono

Appl. Phys. Lett. 96, 252504 (2010); http://dx.doi.org/10.1063/1.3456548 (3 pages) | Cited 3 times

Online Publication Date: 23 June 2010

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The electron transport through the CoFeB/MgO/CoFeB-based magnetic tunneling junction (MTJ) was studied by the shot noise measurement. The obtained Fano factor to characterize the shot noise is very close to unity, indicating the full shot noise, namely, the shot noise in the Schottky limit, both in the parallel and antiparallel magnetization configurations. This means the Poissonian process of the electron tunneling and the absence of the electron–electron correlation in the low bias regime. The shot noise measurements will be a good guideline to make up tunneling criteria for designing MTJ-based spin devices.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.50.Td Noise processes and phenomena
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Magnetization reversal in an individual 25 nm iron-filled carbon nanotube

Palash Banerjee, F. Wolny, D. V. Pelekhov, M. R. Herman, K. C. Fong, U. Weissker, T. Mühl, Yu. Obukhov, A. Leonhardt, B. Büchner, and P. Chris Hammel

Appl. Phys. Lett. 96, 252505 (2010); http://dx.doi.org/10.1063/1.3440951 (3 pages) | Cited 6 times

Online Publication Date: 25 June 2010

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The magnetization reversal and switching behavior of an individual Fe-filled carbon nanotube has been measured using vibrating cantilever magnetometry. We report measurements of the magnetic field at which the 25 nanometer diameter iron core inside the nanotube reverses. The fields at which reversal occurs, characterized by an exceptionally narrow distribution (σH ≤ 1 G at 6.3 K), are determined by thermally activated excitation over a field dependent barrier. The high precision achievable by virtue of measuring individual nanowires allows detailed quantitative understanding of magnetization reversal.
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75.60.Jk Magnetization reversal mechanisms
61.46.Fg Nanotubes
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Magnetic metal cladding gives better attenuation in small waveguides operating at high microwave frequencies than nonmagnetic metals

K. L. Livesey and R. E. Camley

Appl. Phys. Lett. 96, 252506 (2010); http://dx.doi.org/10.1063/1.3457478 (3 pages)

Online Publication Date: 25 June 2010

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We calculate the attenuation in microwave waveguides comprising a thin film of dielectric SiO2 sandwiched by copper or iron films. We show that in a frequency range between roughly 63 and 73 GHz, using iron gives lower losses by up to 7.5 dB/cm compared with copper. This is in the region of so-called antiresonance where the effective skin depth of ferromagnetic iron diverges.
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84.40.Az Waveguides, transmission lines, striplines

Two modes behavior of vortex oscillations in spin-transfer nanocontacts subject to in-plane magnetic fields

Michaela Kuepferling, Claudio Serpico, Matthew Pufall, William Rippard, T. Mitchell Wallis, Atif Imtiaz, Pavol Krivosik, Massimo Pasquale, and Pavel Kabos

Appl. Phys. Lett. 96, 252507 (2010); http://dx.doi.org/10.1063/1.3455883 (3 pages) | Cited 3 times

Online Publication Date: 25 June 2010

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Vortex oscillations induced by dc currents (Idc) through a metallic nanocontact subject to in-plane magnetic fields (Hext) are studied by measuring voltage power spectra. Two oscillations modes exist: at large Idc the oscillation frequency (fosc) is substantially insensitive to Hext, whereas at low Idc, fosc decreases with Hext increasing. At intermediate Idc the two modes coexist. This behavior is ascribed to the magnetic states of the device ferromagnetic layers: in the first mode vortices are formed in both layers while in the second mode one layer is in a vortex state while the other is in a quasiuniform state.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Cc Other ferromagnetic metals and alloys
75.75.Lf Electronic structure of magnetic nanoparticles
75.47.De Giant magnetoresistance
75.75.Fk Domain structures in nanoparticles
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