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Current-voltage (I–V) characteristics of GaAs-based resonant tunneling diodes have been investigated in the presence of a perpendicular magnetic field. Electron resonant tunneling is strongly suppressed by the applied magnetic field, leading to peak current decreasing with increasing magnetic field. The observed plateau-like structures appear in negative differential resistance region on the I–V curves and are magnetic-field dependent. The plateau-like structures are due to the coupling between the energy levels in the emitter well and in the main quantum well. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It has been found by electron diffraction and high-resolution transmission electron microscopy that each commercial CrO[sub 2] particle is enclosed by an epitaxial Cr[sub 2]O[sub 3] layer ∼2.5 nm thick. The epitaxial relationships of Cr[sub 2]O[sub 3] layers on CrO[sub 2] particles have been identified. Magnetic hysteresis loops measured at different temperatures (5–300 K), after the sample was cooled from 350 K with a 50 kOe field, were found to be perfectly symmetrical, i.e., no exchange bias was observed, which is unexpected for ferromagnetic/antiferromagnetic core/shell structured particles. To gain a deeper understanding of the phenomenon, the “as-received” commercial CrO[sub 2] particles were annealed at 600 °C in air for 1 h to thicken the Cr[sub 2]O[sub 3] shells. Exchange bias was clearly observed in the annealed particles with thicker Cr[sub 2]O[sub 3] shells. At 5 K, the exchange bias field reached 220 Oe. These experimental observations can be explained well within the framework of the random field model. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate a class of sonic shield materials based on the principle of locally resonant (LR) microstructures. Each local resonator is found to vibrate almost like an independent unit, and two layers of such resonators can even be regarded as a sonic crystal. By combining several LR layers of different resonant frequencies, a broadband (200–500 Hz) sound shield, with an average transmission intensity 11 dB lower than that dictated by mass density law, has been achieved. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polycrystalline Fe[sub 3]O[sub 4] films have been prepared by reactive sputtering at room temperature. Transmission electron microscopy images show that the films consist of quite uniform Fe[sub 3]O[sub 4] grains well separated by grain boundaries. It was found that the tunneling of spin-polarized electrons across the antiferromagnetic coupled grain boundaries dominates the transport properties of the films. Magnetoresistance (MR) {=[ρ(H)-ρ(0)]/ρ(0)} shows linear and quadratic magnetic-field dependence in the low-field range when the field is applied parallel and perpendicular to film plane, which is similar to the behaviors observed in the epitaxial Fe[sub 3]O[sub 4] films consisting of a large fraction of antiferromagnetic antiphase domain boundaries. At 300 K, the size of the MR reaches -7.4% under a 50-kOe magnetic field, which is a very large MR for polycrystalline Fe[sub 3]O[sub 4] films. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report molecular-beam epitaxy growth of single crystalline ZnSe nanowires with uniform diameters (∼10 nm) on GaP(111) substrates. The growth process was based on the Au-catalyzed vapor-liquid-solid deposition. As determined by electron microdiffraction and high-resolution transmission electron microscopy, ZnSe nanowires grew generally along the <110> and <112> directions with the orientation relationship of (111)[sub ZnSe wire]//(111)[sub GaP] and <110>[sub ZnSe wire]//<110>[sub GaP]. The dominant defects were found to be twins at the interface between the substrate and the nanowires along the (111) plane. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the magnetic and transport properties of a perovskite-type crystal sample with a nominal composition La[sub 0.67]Ca[sub o.33]MnO[sub x]. Temperature range and magnetic field limitation; Exhibition of magnetization data obtained in the zero-field-cooled process; Appearance of an interesting feature in the temperature dependence of magnetoresistance.

Demonstrates the laser performance of niobium-doped strontium fluorapatite (S-FAP) crystal at 1.059 and 1.328 micrometer. Comparison with the laser performance and properties of Nd:YVO[sub 4] crystals; Implication of S-FAP crystals for diode pumped laser applications; Details on the absorption peak and coefficient of S-FAP crystals.

Describes the Czochralski growth of laser-quality Nd[sup 3+]-doped calcium fluorapatite single crystals. Perforamnce of single crystal lasing; Effect of concentration quenching on laser performance; Impact of diode laser use as pump source on laser crystal size.

Examines energy transfer from holmium to ytterbium. Demonstration of energy transfer in fluoride crystals; Relationship of energy transfer and efficiency with temperature; Presentation of the mechanism governing back energy transfer.

Characterizes the laser action of Nd doped gadolinium lithium fluoride (Nd:GLF) in pulsed and crystal whisker laser pumped operation. Spectroscopic and laser properties of Nd:GLF; Comparison of the laser performance with that of the Nd doped lithium yttrium fluoride; Doping of GLF with higher Nd concentration.

Investigates the Cr[sup 4+]-doped Y[sub 2]SiO[sub 5] and Ca[sub 2]Al[sub 2]SiO[sub 7] crystals as broadband, solid state saturable absorbers. Saturation properties in the near infrared; Generation of tunable light with pulse duration of a few tens of nanoseconds; Applications of solid state lasers systems.

Remarkably oxidation-resistant nanoparticles of iron prepared at Tianjin University have been studied by electron diffraction and high-resolution transmission electron microscopy (HRTEM). HRTEM images clearly show the polyhedral epitaxy of γ-Fe[sub 2]O[sub 3] layers on equivalent {100} facets of the {100} truncated {110} rhombic dodecahedral nanoparticles of iron. Oxide layers on {110} facets are formed by the lateral extension of the epitaxial {100} γ-Fe[sub 2]O[sub 3] layers over adjacent {110} facets. The {110} oxide layers are bent and concave inward. The compressive γ-Fe[sub 2]O[sub 3] layers which are about 4 nm thick give effective protection, according to the theory of Caberra-Mott, to the iron core from further oxidation. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A large magnetic entropy change has been observed in an intermetallic compound LaFe[sub 10.6]Si[sub 2.4]. The maximum -ΔS[sub M]approx. 3.2 J/kg K was found at its Curie temperature, ∼242 K, upon a 2 T magnetic field change. Although the entropy change is slightly smaller than that of pure Gd metal, such Fe-rich compounds still appear to be very attractive candidates since (a) the raw materials are much cheaper than pure Gd metal; (b) the Curie temperature can be easily shifted by tuning the composition; (c) the materials are much more chemically stable than pure Gd metal. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]