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29 Dec 2008

Volume 93, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 93, 261101 (2008); http://dx.doi.org/10.1063/1.3053074 (3 pages)

Takashi Fujikura, Osamu Matsuda, Dieter M. Profunser, Oliver B. Wright, Jeremy Masson, and Sylvain Ballandras
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Spin-wave confinement in rolled-up ferromagnetic tubes

Stefan Mendach, Jan Podbielski, Jesco Topp, Wolfgang Hansen, and Detlef Heitmann

Appl. Phys. Lett. 93, 262501 (2008); http://dx.doi.org/10.1063/1.3058764 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2008

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We investigate the spin-wave dispersion in rolled-up Permalloy microtubes based on self-rolling strained semiconductor layers. Using microwave absorption spectroscopy we find that these structures exhibit a characteristic spin-wave mode spectrum. The magnetization and spin-wave resonance at zero external magnetic field is determined by curvature induced dynamic demagnetization fields. At high magnetic fields transverse to the tube axis, the three-dimensional shape anisotropy of the tube results in spin-wave confinement in well-defined regions along the tube perimeter.
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75.30.Ds Spin waves
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.70.Gq Microwave and radio-frequency interactions

Substrate orientation dependence of ferromagnetism in (Ga,Mn)As

M. J. Wilson, G. Xiang, B. L. Sheu, P. Schiffer, N. Samarth, S. J. May, and A. Bhattacharya

Appl. Phys. Lett. 93, 262502 (2008); http://dx.doi.org/10.1063/1.3058758 (3 pages) | Cited 2 times

Online Publication Date: 30 December 2008

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We describe a comprehensive study of the properties of both ordered and random alloy Ga1−xMnxAs grown on (001), (311), (201), and (110) GaAs substrates. Magnetization measurements show a systematic variation in the Curie temperature with epitaxial orientation in both types of samples, even for the same average Mn concentrations. Electrical characterization and thermal annealing of the random alloy Ga1−xMnxAs samples suggest that the density of As antisite defects depends on the growth surface, providing an extrinsic origin for the observed dependence of Curie temperature on substrate orientation.
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75.50.Pp Magnetic semiconductors
75.75.-c Magnetic properties of nanostructures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Fraunhofer regime of operation for superconducting quantum interference filters

A. V. Shadrin, K. Y. Constantinian, G. A. Ovsyannikov, S. V. Shitov, I. I. Soloviev, V. K. Kornev, and J. Mygind

Appl. Phys. Lett. 93, 262503 (2008); http://dx.doi.org/10.1063/1.3058759 (3 pages)

Online Publication Date: 30 December 2008

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Series arrays of superconducting quantum interference devices (SQUIDs) with incommensurate loop areas, so-called superconducting quantum interference filters (SQIFs), are investigated in the kilohertz and the gigahertz frequency range. In SQIFs made of high-Tc bicrystal junctions the flux-to-voltage response ∂V/∂Φ is dominated by the variation in the critical current in the individual junctions (Fraunhofer-type) rather than by the SQUIDs interference. For a SQIF with 20 SQUID loops we find ∂V/∂Φ = 40 mV/Φ0 and a dynamic range of more than 60 dB in the kilohertz range. In the 1–2 GHz range the estimated power gain is 20 dB and the magnetic flux noise level is as low as 10−4Φ0.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.30.Vn Filters
85.25.Cp Josephson devices

High domain wall velocities induced by current in ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy

T. A. Moore, I. M. Miron, G. Gaudin, G. Serret, S. Auffret, B. Rodmacq, A. Schuhl, S. Pizzini, J. Vogel, and M. Bonfim

Appl. Phys. Lett. 93, 262504 (2008); http://dx.doi.org/10.1063/1.3062855 (3 pages) | Cited 54 times

Online Publication Date: 31 December 2008

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Current-induced domain wall (DW) displacements in an array of ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy have been directly observed by wide field Kerr microscopy. DWs in all wires in the array were driven simultaneously and their displacement on the micrometer scale was controlled by the current pulse amplitude and duration. At the lower current densities where DW displacements were observed (j ≤ 1.5×1012 A/m2), the DW motion obeys a creep law. At higher current density (j = 1.8×1012 A/m2), zero-field average DW velocities up to 130±10 m/s were recorded.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects

Effects of donor doping on Ga1−xMnxAs

Y. J. Cho, K. M. Yu, X. Liu, W. Walukiewicz, and J. K. Furdyna

Appl. Phys. Lett. 93, 262505 (2008); http://dx.doi.org/10.1063/1.3063046 (3 pages) | Cited 6 times

Online Publication Date: 31 December 2008

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We investigate the effect compensating Mn acceptors in Ga1−xMnxAs films by doping with Si donors. For Ga1−xMnxAs with low Mn content (e.g., x<0.033), doping by Si decreases the Curie temperature TC compared to undoped Ga1−xMnxAs. At high values of x, however (e.g., x>0.10), Si doping is found to increase TC. We ascribe this to an increase in the hole mobility in high x samples due to changes in the relative occupancy of the hole impurity band associated with compensation by the Si donors.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
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