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27 Mar 2000

Volume 76, Issue 13, pp. 1641-1784

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Crystallographic and magneto-optical studies of nanoscaled MnSb dots grown on GaAs

M. Mizuguchi, H. Akinaga, K. Ono, and M. Oshima

Appl. Phys. Lett. 76, 1743 (2000); http://dx.doi.org/10.1063/1.126153 (3 pages) | Cited 14 times

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MnSb ultrathin films with the nominal thickness of 0–1.40 nm were grown on sulfur passivated GaAs substrates by molecular beam epitaxy. Atomic force microscopy analysis showed that MnSb formed nanosize clusters on the substrate, and the coalescence of the clusters occurred at the nominal thickness between 0.70 and 1.05 nm. The intensity of the polar magnetic circular dichroism of MnSb clusters suddenly increased when the nominal thickness reached the critical value of 1.05 nm. The coalescence among the dots can be correlated with the sharp increase of the magnetic circular dichroism intensity. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Li Other semiconductors
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd Other semiconductors

Nanocomposite Nd-rich Nd–Fe–B alloys: Approaching ideal Stoner–Wohlfarth type behavior

Er. Girt, Kannan M. Krishnan, G. Thomas, and Z. Altounian

Appl. Phys. Lett. 76, 1746 (2000); http://dx.doi.org/10.1063/1.126154 (3 pages) | Cited 20 times

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Starting from rapidly quenched NdδFe13.1B(2.05 ⩽ δ ⩽ 147.6) alloys and by appropriate annealing, the microstructure was tailored from strongly interacting Nd2Fe14B grains to magnetically isolated single domain Nd2Fe14B grains embedded in a nonmagnetic Nd-rich matrix (α-Nd and γ-Nd). This change in microstructure was found to have a large effect on coercivity, i.e., coercivity, μ0Hc, increases with an increase of the Nd concentration from 1.25 T in Nd2.05Fe13.1B to 2.75 T in Nd147.6Fe13.1B at 290 K. Using transmission electron microscopy, the Nd2Fe14B grains in Nd147.6Fe13.1B were confirmed to be randomly oriented platelets with the c axis normal to the plate and an average size of 100×40×25 nm. For these randomly oriented, noninteracting, single domain Nd2Fe14B grains, the coercivity was calculated using a Stoner–Wohlfarth model which included the shape anisotropy of the grains. The observed coercivity of Nd2Fe14B in such nanocomposite Nd147.6Fe13.1B alloys is ∼83% of its theoretical value. © 2000 American Institute of Physics.
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75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.50.Bb Fe and its alloys

Phonon spectrometry with a bolometer based on spin-lattice relaxation

A. M. Witowski, H.-P. Moll, M. L. Sadowski, P. Wyder, G. Karczewski, J. Kossut, and T. Wojtowicz

Appl. Phys. Lett. 76, 1749 (2000); http://dx.doi.org/10.1063/1.126155 (3 pages)

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We discuss the possibility of a bolometer based on the effect of spin-lattice relaxation detected by a pickup coil. The system is composed of an epitaxial layer of CdMnTe on a GaAs substrate, grown by molecular beam epitaxy (MBE). The “phonon wave,” generated by a light pulse on the back surface of the substrate, changes the spin alignment in the MBE layer, thus also changing its magnetization. This change is detected by a pickup coil. The possible use of such a system as a bolometer and “phonon spectrometer” is discussed. © 2000 American Institute of Physics.
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63.20.-e Phonons in crystal lattices
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Linewidth of a resistively shunted high-temperature-superconductor Josephson heterodyne oscillator

J. C. Macfarlane, L. Hao, D. A. Peden, and J. C. Gallop

Appl. Phys. Lett. 76, 1752 (2000); http://dx.doi.org/10.1063/1.126156 (3 pages) | Cited 11 times

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High-temperature-superconducting (HTS) resistively shunted superconducting quantum interference devices, consisting of two yttrium–barium–copper–oxide (YBCO) grain boundary junctions shunted by gold-film resistors of ∼20 μΩ, have been prepared and characterized at temperatures from 17 to 74 K. The small value and stability of the resistor allows narrow-band heterodyne oscillations to be generated between the Josephson oscillations in the individual junctions. The frequency can be precisely controlled in accordance with the ac Josephson effect by adjustment of an external current applied to the YBCO–Au–YBCO shunt resistor, and the linewidth is determined in principle only by Johnson noise in the resistor. Off-chip detection and spectral analysis of the heterodyne signal generated in this way has not been previously reported. Measurements of the signal power (∼nW), the tunability of the center frequency from 5 to 50 MHz, the frequency stability and the linewidth of the heterodyne Josephson oscillation are described. Although linewidth broadening due to nonthermal fluctuations is observed, the linewidth of ∼30 kHz at T = 17 K, at a center frequency of 24 MHz, is believed to be the narrowest reported for Josephson oscillations in an HTS device of this type. © 2000 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.72.-h Cuprate superconductors
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures
74.40.-n Fluctuation phenomena

Low angle grain boundary transport in YBa2Cu3O7−δ coated conductors

D. T. Verebelyi, D. K. Christen, R. Feenstra, C. Cantoni, A. Goyal, D. F. Lee, M. Paranthaman, P. N. Arendt, R. F. DePaula, J. R. Groves, and C. Prouteau

Appl. Phys. Lett. 76, 1755 (2000); http://dx.doi.org/10.1063/1.126157 (3 pages) | Cited 99 times

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Second generation, high-temperature superconducting wires are based on buffered, metallic tape substrates of near single crystal texture. Strong alignment of adjacent grains was found to be necessary from previous work that suggested large angle, YBa2Cu3O7−δ [001]-tilt boundaries reduce Jc exponentially with increasing misorientation angle (θ). We pursue the low-θ regime by evaluating single grain boundaries (GB) and biaxially aligned polycrystalline films utilizing both the rolling-assisted biaxially textured substrates and ion-beam assisted deposition coated conductor architectures. Analysis concludes that an exponential dependence on Jc is applicable for θ≳4°, where the spacing between the periodic disordered regions along the GB become smaller than a coherence length. © 2000 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
74.25.Sv Critical currents
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