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26 Dec 2011

Volume 99, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 99, 261101 (2011); http://dx.doi.org/10.1063/1.3660243 (3 pages)

T. Schwarzbäck, H. Kahle, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler
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Tuning the surface magnetism of γ-Fe2O3 nanoparticles with a Cu shell

R. D. Desautels, E. Skoropata, Y.-Y. Chen, H. Ouyang, J. W. Freeland, and J. van Lierop

Appl. Phys. Lett. 99, 262501 (2011); http://dx.doi.org/10.1063/1.3671989 (4 pages) | Cited 3 times

Online Publication Date: 27 December 2011

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An interfacial monolayer of CuO in Cu-coated γ-Fe2O3 nanoparticles enables significantly decreased intrinsic surface spin disorder compared to bare γ-Fe2O3 nanoparticles. Element specific x-ray absorption spectroscopy at the L-edges for Cu and Fe indicates that the magnetic moment of the CuO in the shell interacts with the γ-Fe2O3 nanoparticle’s surface magnetic moments. This exchange interaction cants the moments of the CuO resulting in a non-zero Cu moment, altering the γ-Fe2O3 nanomagnetism.
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75.70.Rf Surface magnetism
75.50.Tt Fine-particle systems; nanocrystalline materials
78.70.Dm X-ray absorption spectra
75.30.Cr Saturation moments and magnetic susceptibilities

Coherence in a transmon qubit with epitaxial tunnel junctions

Martin P. Weides, Jeffrey S. Kline, Michael R. Vissers, Martin O. Sandberg, David S. Wisbey, Blake R. Johnson, Thomas A. Ohki, and David P. Pappas

Appl. Phys. Lett. 99, 262502 (2011); http://dx.doi.org/10.1063/1.3672000 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2011

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We developed transmon qubits based on epitaxial tunnel junctions and interdigitated capacitors. This multileveled qubit, patterned by use of all-optical lithography, is a step towards scalable qubits with a high integration density. The relaxation time T1 is 0.72−0.86 μs and the ensemble dephasing time T2* is slightly larger than T1. The dephasing time T2 (1.36 μs) is nearly energy-relaxation-limited. Qubit spectroscopy yields weaker level splitting than observed in qubits with amorphous barriers in equivalent-size junctions. The qubit’s inferred microwave loss closely matches the weighted losses of the individual elements (junction, wiring dielectric, and interdigitated capacitor), determined by independent resonator measurements.
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84.32.Tt Capacitors

Fast switching of magnetization in the ferromagnetic semiconductor (Ga,Mn)(As,P) using nonequilibrium phonon pulses

A. Casiraghi, P. Walker, A. V. Akimov, K. W. Edmonds, A. W. Rushforth, E. De Ranieri, R. P. Campion, B. L. Gallagher, and A. J. Kent

Appl. Phys. Lett. 99, 262503 (2011); http://dx.doi.org/10.1063/1.3672029 (3 pages) | Cited 1 time

Online Publication Date: 28 December 2011

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We use short acoustic pulses to induce a fast irreversible switching of the magnetization orientation in a layer of (Ga,Mn)(As,P). The pulses are generated by femtosecond optical excitation of a metal transducer film and travel ballistically through the sample. We show that the switching is triggered by incoherent acoustic phonons, occurs through domain-related processes, and is concluded in ∼35 ns. We suggest that the mechanism behind the switching involves the holes in the material being heated due to their coupling to the phonons.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Gw Magnetic anisotropy

Magnon magnetoresistance of NiFe nanowires: Size dependence and domain wall detection

V. D. Nguyen, C. Naylor, L. Vila, A. Marty, P. Laczkowski, C. Beigné, L. Notin, Z. Ishaque, and J. P. Attané

Appl. Phys. Lett. 99, 262504 (2011); http://dx.doi.org/10.1063/1.3672828 (3 pages) | Cited 3 times

Online Publication Date: 28 December 2011

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The magnetoresistance of permalloy (Ni84Fe16) nanowires of various widths (down to 50 nm) has been measured for fields applied along the wires. The enhancement of the shape anisotropy in the narrowest widths leads to the disappearance of the anisotropic magnetoresistance signal, the remaining contribution to the magnetoresistance being that of the magnons. Using constrictions to pin a domain wall, we show that the magnon magnetoresistance signal can give access to the position of the domain wall along the wire.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Ds Spin waves
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.75.-c Magnetic properties of nanostructures

All-electrical operation of magnetic vortex core memory cell

K. Nakano, D. Chiba, N. Ohshima, S. Kasai, T. Sato, Y. Nakatani, K. Sekiguchi, K. Kobayashi, and T. Ono

Appl. Phys. Lett. 99, 262505 (2011); http://dx.doi.org/10.1063/1.3673303 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2011

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A single vortex-core switching in a ferromagnetic disk is detected in real time by using a three-terminal device with the tunneling magnetoresistance junction. We show that the device works as a vortex core memory cell, where reading and writing can be done in an all-electrical way: binary data corresponding to the core direction can be read out electrically as the amplitude of the output, while the data can be written electrically by applying a pulsed current.
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85.70.-w Magnetic devices

Spin-transfer mechanism for magnon-drag thermopower

M. E. Lucassen, C. H. Wong, R. A. Duine, and Y. Tserkovnyak

Appl. Phys. Lett. 99, 262506 (2011); http://dx.doi.org/10.1063/1.3672207 (3 pages) | Cited 1 time

Online Publication Date: 30 December 2011

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We point out a relation between the dissipative spin-transfer-torque parameter β and the contribution of magnon drag to the thermoelectric power in conducting ferromagnets. Using this result, we estimate β in iron at low temperatures, where magnon drag is believed to be the dominant contribution to the thermopower. Our results may be used to determine β from magnon-drag-thermopower experiments, or, conversely, to infer the strength of magnon drag via experiments on spin transfer.
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72.25.-b Spin polarized transport
75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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