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17 Jan 2005

Volume 86, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 033101 (2005); http://dx.doi.org/10.1063/1.1851002 (3 pages)

Kun Chen, Allen Taflove, Young L. Kim, and Vadim Backman
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Josephson junctions with nonlinear damping for rapid single-flux-quantum - qubit circuits

A. B. Zorin, M. I. Khabipov, D. V. Balashov, R. Dolata, F.-I. Buchholz, and J. Niemeyer

Appl. Phys. Lett. 86, 032501 (2005); http://dx.doi.org/10.1063/1.1852076 (3 pages) | Cited 10 times

Online Publication Date: 7 January 2005

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We demonstrate that shunting of superconductor-insulator-superconductor (S-I-S) Josephson junctions by superconductor-insulator-normal metal (S-I-N) structures having pronounced nonlinear I–V characteristics can remarkably modify the Josephson dynamics. In the regime of Josephson generation the phase behaves as an overdamped coordinate, while in the superconducting state the damping and current noise are strikingly small, that is vitally important for application of such junctions for readout and control of Josephson qubits. Superconducting Nb/AlOx/Nb junction shunted by Nb/AlOx/AuPd junction of S-I-N type was fabricated and, in agreement with our model, exhibited nonhysteretic I–V characteristics at temperatures down to at least 1.4 K.
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85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
85.25.Cp Josephson devices

High sensitivity of positive magnetoresistance in low magnetic field in perovskite oxide p–n junctions

H. B. Lu, S. Y. Dai, Z. H. Chen, Y. L. Zhou, B. L. Cheng, K. J. Jin, L. F. Liu, G. Z. Yang, and X. L. Ma

Appl. Phys. Lett. 86, 032502 (2005); http://dx.doi.org/10.1063/1.1850192 (3 pages) | Cited 57 times

Online Publication Date: 7 January 2005

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Large positive magnetoresistance (MR) and high MR sensitivity in low magnetic fields have been discovered in the Sr-doped LaMnO3 and Nb-doped SrTiO3 p–n junctions fabricated by laser molecular-beam epitaxy. The MR ratios, defined as ΔR/R0, ΔR = RH−R0, are observed as large as 11% in 5 Oe, 23% in 100 Oe, and 26% in 1000 Oe at 290 K; 53% in 5 Oe, 80% in 100 Oe, and 94% in 1000 Oe at 255 K. The MR sensitivities are 85 Ω/Oe at 290 K, 246 Ω/Oe at 255 K, and 136 Ω/Oe at 190 K, respectively, with the applied magnetic field changed from 0 to 5 Oe. The positive MR ratios and high MR sensitivities of the p–n junctions are very different from that of the LaMnO3 compound family.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.50.Dd Nonmetallic ferromagnetic materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
73.43.Qt Magnetoresistance
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ng Insulators
75.47.Lx Magnetic oxides
68.55.-a Thin film structure and morphology
42.62.-b Laser applications

In situ detection method for obtaining permeability of Fe-based amorphous alloys: ac resistance measurement for Fe84Nb7B9

Tetsu Ichitsubo, Eiichiro Matsubara, Satoshi Tanaka, Nobuyuki Nishiyama, and Kenji Amiya

Appl. Phys. Lett. 86, 032503 (2005); http://dx.doi.org/10.1063/1.1852713 (3 pages) | Cited 1 time

Online Publication Date: 7 January 2005

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In this letter, we propose an in situ detection method for obtaining permeability of soft magnetic Fe-based amorphous alloys. The temperature dependence of ac resistance was measured at different frequencies during heat treatment of Fe84Nb7B9 amorphous alloys. A significant increase in the ac ( ∼ 1000 kHz) resistance appears at around 920 K during the heating process, which arises from the skin effect caused by a marked increase in sample permeability. This skin effect diminishes when the sample is heated to approximately 1100 K, which corresponds to the decrease in its permeability. Consequently, we note that the ac resistance measurement is useful for quick in situ assessment to achieve the soft magnetic property of an Fe-based amorphous alloy.
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75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.05.Bx Metals, semimetals, and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys
81.40.Gh Other heat and thermomechanical treatments
72.30.+q High-frequency effects; plasma effects

Domain wall coupling and collective switching in interacting mesoscopic ring magnet arrays

M. Kläui, C. A. F. Vaz, J. A. C. Bland, and L. J. Heyderman

Appl. Phys. Lett. 86, 032504 (2005); http://dx.doi.org/10.1063/1.1846954 (3 pages) | Cited 20 times

Online Publication Date: 7 January 2005

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The effects of magnetostatic domain wall coupling on the magnetic switching are investigated for micrometer-sized cobalt ring arrays with edge-to-edge spacings varying between 80 nm and 8 μm. The various transitions between the different equilibrium states in rings are affected differently with increasing magnetostatic interaction (leading to an increased or reduced switching field) depending on the details of the particular switching mechanism. The switching field distribution width is strongly reduced for narrowly spaced ring arrays due to collective switching between adjacent rings where the domain walls couple magnetostatically. The interaction is found to increase with increasing film thickness due to the increased stray field.
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75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
75.30.Et Exchange and superexchange interactions
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.-a Thin film structure and morphology

Rare earth ion size effects and enhanced critical current densities in Y2/3Sm1/3Ba2Cu3O7−x coated conductors

J. L. MacManus-Driscoll, S. R. Foltyn, B. Maiorov, Q. X. Jia, H. Wang, A. Serquis, L. Civale, Y. Lin, M. E. Hawley, M. P. Maley, and D. E. Peterson

Appl. Phys. Lett. 86, 032505 (2005); http://dx.doi.org/10.1063/1.1851006 (3 pages) | Cited 26 times

Online Publication Date: 10 January 2005

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The influence of rare earth (RE) ion size on critical current density (Jc) in epitaxial films of superconducting REBa2Cu3O7−x was studied, where RE is the mixture of two or three rare earth ions. No systematic dependence of Jc on RE ion size was found. However, strongly enhanced critical current densities (Jc’s) were found for the composition Y2/3Sm1/3Ba2Cu3O7−x (YSmBCO). In ∼ 1‐μm-thick films, Jc’s as high as 4.7×106 A cm−2 (75.5 K, 0 T) and 11×104 A cm−2 (75.5 K, 5 T) were obtained on single crystals and 6×104 A cm−2 (75.5 K, 5 T) on buffered metal. The values are up to a factor of 3 higher than for comparative YBCO samples.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents

Ferromagnetic Mn-doped GaN nanowires

Doo Suk Han, Jeunghee Park, Kung Won Rhie, Soonkyu Kim, and Joonyeon Chang

Appl. Phys. Lett. 86, 032506 (2005); http://dx.doi.org/10.1063/1.1852725 (3 pages) | Cited 43 times

Online Publication Date: 10 January 2005

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We report Mn-doped GaN nanowires exhibiting ferromagnetism even at room temperature. The growth of single-crystalline wurtzite-structured GaN nanowires doped homogeneously with about 5 at. % Mn was achieved by chemical vapor deposition using the reaction of Ga∕GaN∕MnCl2 with NH3. The ferromagnetic hysteresis at 5 and 300 K and the temperature-dependent magnetization curves suggest the Curie temperature around 300 K. Negative magnetoresistance of individual nanowires was observed at the temperatures below 150 K.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Pq Other materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.20.Uv Electron energy loss spectroscopy

Electron paramagnetic resonance studies of the high-spin molecule Cr10(OMe)20(O2CCMe3)10

Sonia Sharmin, Arzhang Ardavan, Stephen J. Blundell, Amalia I. Coldea, Eric J. L. McInnes, and David Low

Appl. Phys. Lett. 86, 032507 (2005); http://dx.doi.org/10.1063/1.1851613 (3 pages) | Cited 3 times

Online Publication Date: 12 January 2005

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We report millimeter-wave magneto-optical measurements on the high-spin molecule, Cr10(OMe)20(O2CCMe3)10. The dependence of the electron paramagnetic resonance as a function of orientation and temperature demonstrates that this compound behaves as a single molecule magnet, and exhibits one of the smallest zero-field splittings (D = −0.045±0.004 K) yet reported for such a system.
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75.50.Xx Molecular magnets
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
78.70.Gq Microwave and radio-frequency interactions
78.20.Ls Magneto-optical effects
75.10.Dg Crystal-field theory and spin Hamiltonians

Magnetoelectric resonance-bandwidth broadening of Terfenol-D/epoxy-Pb(Zr,Ti)O3 bilayers in parallel and series connections

H. Yu, M. Zeng, Y. Wang, J. G. Wan, and J.-M. Liu

Appl. Phys. Lett. 86, 032508 (2005); http://dx.doi.org/10.1063/1.1854736 (3 pages) | Cited 15 times

Online Publication Date: 12 January 2005

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The bandwidth of magnetoelectric (ME) resonance for a combined structure where several Terfenol-D/epoxy-Pb(Zr,Ti)O3 bilayers are connected in parallel and series was measured. A relationship between the bilayer length and resonance frequency was used to design the combined structure, in which the bilayered components of different lengths were connected in the parallel and series forms, respectively. The measured giant ME effect of the combined structure showed a much wider frequency response to external field than a single bilayered structure, and the ME effect far from the resonance ranges was enhanced significantly too. A qualitative analysis based on the equivalent circuit concept was presented to explain these effects.
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75.80.+q Magnetomechanical effects, magnetostriction
77.55.-g Dielectric thin films
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
77.65.Fs Electromechanical resonance; quartz resonators
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Growth of ferromagnetic nanoparticles in Ge:Fe thin films

R. Goswami, G. Kioseoglou, A. T. Hanbicki, O. M. J. van ’t Erve, B. T. Jonker, and G. Spanos

Appl. Phys. Lett. 86, 032509 (2005); http://dx.doi.org/10.1063/1.1854743 (3 pages) | Cited 15 times

Online Publication Date: 12 January 2005

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The microstructure and magnetic properties of Ge:Fe thin films grown by molecular-beam epitaxy have been studied by transmission electron microscopy and superconducting quantum interference device magnetometry. Films were deposited on GaAs(001) at substrate temperatures (TS) ranging from 70 to 400 °C. Nanoparticles of ferromagnetic Fe3Ge2 form in a single-crystalline Ge matrix for TS ≥ 150 °C. The evolution of magnetic order has been evaluated as the particle size increases from 2 nm at TS = 150 °C to 15 nm at 400 °C. The ferromagnetic order of Ge:Fe nanocomposite thin films originates solely from ferromagnetic second-phase particles.
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75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.50.Bb Fe and its alloys
81.16.-c Methods of micro- and nanofabrication and processing
81.05.Cy Elemental semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.-w Structure of nanoscale materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.S- Impurities in crystals
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.Nq Composition and phase identification
68.37.Lp Transmission electron microscopy (TEM)

Capping layer effects in the structure and composition of Co nanoparticle ultrathin films

J. Arbiol, F. Peiró, A. Cornet, C. Clavero, A. Cebollada, G. Armelles, and Y. Huttel

Appl. Phys. Lett. 86, 032510 (2005); http://dx.doi.org/10.1063/1.1854746 (3 pages) | Cited 8 times

Online Publication Date: 12 January 2005

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In this work, we present the correlation of the magnetic and structural properties of Co nanoparticles deposited by sputtering on Si3N4 substrates at different temperatures, and covered with different capping layers, two insulators, AlN and MgO, and a metal, Pt. High-resolution transmission electron microscopy shows the formation of CoPt3 and Co2N, for the Pt and AlN capping layers, respectively, giving to a significant change of the magnetic behavior. When using a cap of MgO, energy-filtered transmission electron microscopy shows an oxidized shell covering the Co nanoparticles with thickness decreasing as the deposition temperature increases, explaining the changes in the magnetic response induced by the MgO capping layer.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
75.75.-c Magnetic properties of nanostructures
68.37.Lp Transmission electron microscopy (TEM)

Destruction of spin cycloid in (111)c-oriented BiFeO3 thin films by epitiaxial constraint: Enhanced polarization and release of latent magnetization

Feiming Bai, Junling Wang, M. Wuttig, JieFang Li, Naigang Wang, A. P. Pyatakov, A. K. Zvezdin, L. E. Cross, and D. Viehland

Appl. Phys. Lett. 86, 032511 (2005); http://dx.doi.org/10.1063/1.1851612 (3 pages) | Cited 126 times

Online Publication Date: 14 January 2005

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In BiFeO3 films, it has been found that epitaxial constraint results in the destruction of a space modulated spin structure. For (111)c films, relative to corresponding bulk crystals, it is shown (i) that the induced magnetization is enhanced at low applied fields; (ii) that the polarization is dramatically enhanced; whereas, (iii) the lattice structure for (111)c films and crystals is nearly identical. Our results evidence that eptiaxial constraint induces a transition between cycloidal and homogeneous antiferromagnetic spin states, releasing a latent antiferromagnetic component locked within the cycloid.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Two- and three-dimensional connectivity and current distribution in YBa2Cu3Ox-coated conductors

D. C. van der Laan, M. Dhallé, H. J. N. van Eck, A. Metz, B. ten Haken, H. H. J. ten Kate, L. M. Naveira, M. W. Davidson, and J. Schwartz

Appl. Phys. Lett. 86, 032512 (2005); http://dx.doi.org/10.1063/1.1855414 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2005

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The microstructure of YBa2Cu3Ox (YBCO)-coated conductors depends strongly on the deposition method and thickness of the YBCO layer. This letter shows how the clear qualitative difference in grain connectivity between vacuum-deposited and solution-grown layers has direct consequences for the spatial distribution of the critical current density (Jc). Pulsed-laser-deposited YBCO conductors usually have a columnar grain structure that results in a two-dimensional current network, as demonstrated with magneto-optical imaging. Consequently, their transport Jc varies considerably on length scales from 50 μm up to 5 mm, with current suppression occurring even at defects that run parallel to the macroscopic current. In contrast, the thicker YBCO coatings in metalorganic-deposited samples have a layered structure, leading to a three-dimensional current path. Magneto-optically, this is deduced from sample-wide shielding currents, while transport experiments reveal much smaller spatial variations in Jc. These results are encouraging for the further development of nonvacuum produced YBCO-coated conductors, since such three-dimensional systems are inherently more “forgiving” of local defects.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Sv Critical currents
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries

Pseudo-half-metallicity in the double perovskite Sr2CrReO6 from density-functional calculations

G. Vaitheeswaran, V. Kanchana, and A. Delin

Appl. Phys. Lett. 86, 032513 (2005); http://dx.doi.org/10.1063/1.1855418 (3 pages) | Cited 36 times

Online Publication Date: 14 January 2005

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The electronic structure of the spintronic material Sr2CrReO6 is studied by means of full-potential linear muffin-tin orbital method. Scalar relativistic calculations predict Sr2CrReO6 to be half-metallic with a magnetic moment of 1 μB. When spin–orbit coupling is included, the half-metallic gap closes into a pseudo-gap, and an unquenched rhenium orbital moment appears, resulting in a significant increase of the total magnetic moment to 1.28 μB. This moment is significantly larger than the experimental moment of 0.9 μB. A possible explanation of this discrepancy is that the anti-site disorder in Sr2CrReO6 is significantly larger than hitherto assumed.
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75.50.Dd Nonmetallic ferromagnetic materials
71.20.Ps Other inorganic compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.30.Cr Saturation moments and magnetic susceptibilities
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.15.Rf Relativistic effects
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