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18 Mar 2002

Volume 80, Issue 11, pp. 1859-2034

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Microstructure and magnetic properties of uncoupled Sm2Co17–Cu nanocomposites

J. X. Zhang, L. Bessais, C. Djéga-Mariadassou, E. Leroy, A. Percheron-Guégan, and Y. Champion

Appl. Phys. Lett. 80, 1960 (2002); http://dx.doi.org/10.1063/1.1461070 (3 pages) | Cited 6 times

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Nanocomposite Sm2Co17–Cu particles have been fabricated by low energy comilling of mechanically alloyed Sm2Co17 particles with Cu nanoparticles. The x-ray diffraction analyses show that the diffraction crystallite size (DCS) of Sm2Co17 decreases with increasing comilling time. Scanning and transmission electron microscopy observation demonstrates that the particle size is in the range of the DCS and the Sm2Co17 particles are separated by Cu particles. The coercivity as well as the remanence ratio decreases with increasing milling time due to the grain size reduction and grain separation. The nanocomposite Sm2Co17–Cu exhibits suitable magnetic and microstructure properties for high-density recording. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Epitaxial titanium diboride films grown by pulsed-laser deposition

H. Y. Zhai, H. M. Christen, C. Cantoni, A. Goyal, and D. H. Lowndes

Appl. Phys. Lett. 80, 1963 (2002); http://dx.doi.org/10.1063/1.1461869 (3 pages) | Cited 4 times

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Epitaxial, smooth, and low-resistivity titanium diboride (TiB2) films have been grown on SiC substrates using pulsed-laser deposition. Combined studies from ex situ x-ray diffraction and in situ reflection high-energy electron diffraction indicate the crystallographic alignment between TiB2 and SiC both parallel and normal to the substrate. Atomic force microscopy and scanning electron microscopy studies show that these epitaxial films have a smooth surface, and the resistivity of these films is comparable to that of single-crystal TiB2. Growth of these films is motivated by this material’s structural and chemical similarity and lattice match to the newly discovered superconductor MgB2, both to gain further insight into the physical mechanisms of diborides in general and, more specifically, as a component of MgB2-based thin-film heterostructures.© 2002 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.At Metal and metallic alloys

Study of interface structure of α-Fe/Nd2Fe14B nanocomposite magnets

X. Y. Zhang, Y. Guan, and J. W. Zhang

Appl. Phys. Lett. 80, 1966 (2002); http://dx.doi.org/10.1063/1.1456950 (3 pages) | Cited 16 times

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In this study, the interface structure of α-Fe/Nd2Fe14B nanocomposite magnets has been investigated by employing both the positron lifetime spectroscopy and the two-detector Doppler broadening measurements of the positron–electron annihilation γ quanta. Positron lifetime studies show that there are two kinds of interface structures in the magnets. One characterized by a positron lifetime of 155 ps is determined to be the interfacial amorphous layer. The other has a slack atomic structure in which structural free volumes, which were detected to be predominantly surrounded by nonmagnetic atoms Nd and B by the Doppler broadening measurements, have a larger size than that of one to two lattice vacancies of Fe. This is believed to weaken the magnetic exchange coupling between α-Fe and Nd2Fe14B grains in the nanocomposites. © 2002 American Institute of Physics.
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68.35.Ct Interface structure and roughness
75.50.Bb Fe and its alloys
78.70.Bj Positron annihilation
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Et Exchange and superexchange interactions

Tunneling magnetoresistance in fully epitaxial MnAs/AlAs/MnAs ferromagnetic tunnel junctions grown on vicinal GaAs(111)B substrates

Satoshi Sugahara and Masaaki Tanaka

Appl. Phys. Lett. 80, 1969 (2002); http://dx.doi.org/10.1063/1.1461425 (3 pages) | Cited 30 times

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We have fabricated fully epitaxial single-crystal MnAs/AlAs/MnAs magnetic tunnel junctions (MTJs) grown by molecular-beam epitaxy on vicinal GaAs(111)B substrates. After the bottom MnAs layer was grown at 250 °C, the successive AlAs tunnel barrier and the top MnAs layer were grown at a lower temperature of 200 °C in order to suppress the surface segregation of Mn atoms. High-resolution transmission electron microscopy revealed that a monocrystalline MnAs/AlAs/MnAs trilayer heterostructure with atomically flat and chemically abrupt interfaces was realized. Tunneling magnetoresistance (TMR) was clearly observed in fully epitaxal MTJs made up of this trilayer heterostructure. The TMR ratio was 1.4% at 10 K and it decreased with increasing the bias voltage and with increasing temperature, but the TMR effect still remained at room temperature. © 2002 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
75.50.Cc Other ferromagnetic metals and alloys
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)

Accurate measurements of quantum voltage steps on arrays of bicrystal Josephson junctions

A. M. Klushin, R. Behr, K. Numssen, M. Siegel, and J. Niemeyer

Appl. Phys. Lett. 80, 1972 (2002); http://dx.doi.org/10.1063/1.1458072 (3 pages) | Cited 15 times

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Quantum voltages of an array of YBa2Cu3O7 bicrystal junctions were calibrated against a programmable Josephson array voltage standard. We demonstrated that steps of the current–voltage characteristic of an array of bicrystal junctions at voltages of about 9 mV were flat over the current range of about 80 μA to within six parts in 108. The coincidence of quantum voltages on the array of high-temperature superconductor junctions at 64 K and the reference voltage on the array of niobium junctions at 4.2 K was measured with an uncertainty of two parts in 108. With the same uncertainty, we revealed the coincidence of the Josephson constant KJ ≡ h/2e in YBa2Cu3O7 and in metallic superconductors. © 2002 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.72.-h Cuprate superconductors
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
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