bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic Measurements on Stressed and Stress Relieved La0.66Ca0.33MnO3 Thin Films
Authors: Habermeier H.-U. , Praus R. B. , Gross G. M. , Razavi F. S. 
Published: April 2011

AbstractIn general, epitaxially grown thin films are biaxially stressed if the lattice mismatch of substrate and film is below 2%. We have used epitaxial strain as an extrinsic source of tensile stress exerted to La0.66Ca0.33 MnO3 thin films deposited on SrTiO3 single crystal substrates. The average stress in the film is a function of film thickness and post deposition annealing. Thickness variation and annealing procedures have been used to explore the stress dependence of the characterisics of magnetization curves of the stressed films. It could be shown that the inflection point of the magnetization curve which determines the transition from Blochwall movements to rotations of the magnetization vector and the Rayleigh constant of the virgin magnetization curve are correlated with the stress of the films in analogy to results obtained for plastically deformed single crystals of conventional ferromagnetic metals.
Conductivity and NMR Study of LaGa1−xMnxO3 Single Crystals
Authors: Noginova N. , Loutts G. , Mattix L. , Babalola K. , Arthur E. 
Published: April 2011

AbstractElectrical conductivity and magnetic relaxation has been studied in single crystals of Mn doped LaGaO3 with doping concentrations of 0%, 0.5%, 2%, 10% and 50%. The resistivity of the crystals strongly depends on temperature and can be described with the hopping model. Both activation energy and resistivity coefficient grow significantly with decrease in Mn ion concentrations. Dramatic changes are observed in 71Ga NMR spin-lattice relaxation times.
Spin/Orbital Modulation in Perovskite Manganite Superlattices
Authors: Izumi M. , Manako T. , Kawasaki M. , Tokura Y. 
Published: April 2011

AbstractA systematic study is presented for structural characterization and physical properties of two kinds of perovskite oxide superlattices composed of ferromagnetic (FM) and antiferromagnetic (AF) layers. Spin ordering structures is modulated in FM La0.6Sr0.4MnO3/G-type AF La0.6Sr0.4FeO3 superlattices, whereas, ordering structures both in spin and orbital are modulated in La0.6Sr0.4MnO3/A-type AF La0.45Sr0.55MnO3 along the growth directions. Large magnetoresistance subsists down to low temperature in La0.6Sr0.4MnO3/La0.6Sr0.4 Fe3 (F/G) superlattices as a result of recovery of ferromagnetism, which is once suppressed by spin frustration at the interface between FM and G-type AF layers. In contrast, the constituent layers in the La0.6Sr0.4MnO3/La0.45Sr0.55MnO3 (F/A) superlattices appear to keep their ground states due to the absence of spin frustration at the interface. Magnetoresistance is pronounced in this type of superlattices at low temperatures when the AF layer is very thin, indicating restoration of the electronic coupling between the neighboring FM layers which are otherwise decoupled by intervening A-type AF spin ordering and dx2−y2 orbital ordering in La0.45Sr0.55MnO3 layers.
Magnetotransport and Interface Magnetism in Manganite Heterostructures: Implications for Spin Polarized Tunneling
Authors: Jo Moon-Ho , Mathur N.D. , Evetts J.E. , Blamire M.G. 
Published: April 2011

AbstractThe electronic and magnetic structure at surfaces and interfaces in mixed valence manganites is an active area of research. To study localized properties of interface magnetism in heterostructures we have conducted both current in-plane and current perpendicular-plane measurements in multilayers and trilayer tunnel junctions, respectively. Initial study of the transport in multilayers, consisting of alternating La0.7Ca0.3MnO3 and SrTiO3 with different layer thickness provided information on vertical inhomogeniety in the manganite layers and disordered interfaces. Issues of lattice mismatched strain, structural inhomogeniety were addressed. Trilayer tunnel junctions have been fabricated with the aim of correlating tunneling magnetoresistance to the interface magnetism deduced from multilayer measurements. We describe devices incorporating a novel barrier material which have yielded single domain switchings and very high TMR values above 77 K.
Phase Equilibrium Diagrams of the Binary Systems LaMnO3-SrMnO3 and LaMnO3-CaMnO3
Authors: Majewski Peter , Epple Lars , Schluckwerder Heike , Aldinger Fritz 
Published: April 2011

AbstractThe quasi binary systems LaMnO3 – SrMnO3 and LaMnO3 – CaMnO3 have been studied. Both systems show a miscibility gap below about 1400°C in air. This phenomenon causes the decomposition of single phase (La,Sr)MnO3−x and (La,Ca)MnO3−x solid solution with intermediate La:Sr or La:Ca ratios into La rich SrMnO3−x or CaMnO3−x and Sr or Ca rich LaMnO3−x at lower temperatures. At 1400°C a structure transformation of (La,Sr)MnO3 from orthorhombic to rombohedral has not been observed and the structure of La0.7Sr0.3MnO3 has been determined to be orthorhombic with a = 0.54927 ± 0.0009 nm, b = 0.54582 ± 0.0009 nm, and c = 0.76772 ± 0.0034 nm.
Enhancement of the CMR Effect Near Room Temperature by Defects and Structural Transitions in La1−x−yCaxSryMnO3
Authors: Kolesnik S. , Dabrowski B. , Bukowski Z. , Mais J. 
Published: April 2011

AbstractWe have studied magnetoresistance of a series of La1−xSrxMnO3 and La1−x−yCaxSryMnO3 samples, for which structural and ferromagnetic transformation temperatures are in close proximity. On cooling in zero magnetic field, we observe a rapid increase of resistivity just above TC for La1−xSrxMnO3 samples with x < 0.1425 and x ≤ 0.1725 due to the O*-O' and R-O* - structural phase transformations, respectively. This increase is followed by a rapid decrease due to the ferromagnetic transition. The applied magnetic field significantly shifts the ferromagnetic transition to higher temperatures and suppresses the structure-related resistivity increase. We show that a combination of structural and ferromagnetic transitions gives rise to an enhancement of the negative magnetoresistance due to strong spin-lattice coupling. By choosing a proper composition, the enhancement can be optimized to appear in relatively low magnetic fields. A proper selection of Sr and Ca contents in La1−x−yCaxSryMnO3 and preparation conditions leads to an enhancement of the magnetoresistance effect at room temperature.
Epitaxial La0.7(Pb1−xSrx)0.3MnO3 Thin CMR Film Room Temperature Bolometer
Authors: Lisauskas A. , Khartsev S.I. , Grishin A.M. 
Published: April 2011

AbstractUsing pulsed laser deposition technique we fabricated films of a continuous series of solid solutions La0.7(Pb1−xSrx)0.3MnO3, which undergo metal-to-insulator phase transition close and above room temperature. The optimal composition for uncooled bolometer applications was found at x = 0.37 with maximum of TCR = 7.4 %K−1@ 295 K. Room temperature bolometer demonstrator has been built and tested. Relatively low excess noise (magnitude γ/n of 3·10−21 cm−3) and high TCR enabled achievement of high signal-to-noise ratio of 8·106 √-Hz/K. The observed frequency dispersion of bolometer response has been ascribed to three relaxation mechanisms of the heat transfer: from film thermistor to substrate, from substrate to thermostat, and heat transfer via leads. For fabricated bolometer heat transfer from substrate to thermostat was found to be the slowest one with a time constant of 0.5 s (correspondent substrate-to-thermostat thermal conductance is G = 3·10−3 W/K). Bolometer performance test yields the responsivity ℜ = 0.6 V/W, detectivity D = 9·106 cm√Hz/W and noise equivalent power NEP of 3·10−8 W/√Hz at 30 Hz frame frequency. Further improvement of bolometer thermal isolation using the micromachining technique is believed to achieve the responsivity about 4·103 V/W and detectivity higher than 109 cm√Hz/W@30 Hz.
Ferromagnetic Resonance in Single Crystal Bismuth Iron Garnet Films
Authors: Denysenkov V. , Jalali-Roudsar A. , Adachi N. , Khartsev S. , Grishin A. , Okuda T. 
Published: April 2011

AbstractAmong other magneto-optic materials bismuth substituted yttrium iron garnet (BixY1−x)3 Fe5O12 has the highest Faraday rotation effect in visible region. Completely substituted bismuth iron garnet Bi3Fe5O12 (BIG) films have been grown by pulsed laser deposition technique onto (111) (NdGd)3(ScGa)5O12 single crystal with lattice constant of 12.623 Å. X-ray diffraction proves epitaxial film quality. VSM measurements yield the saturation magnetization 4πMs, = 1100 G and coercive field is about 50 Oe. Ferromagnetic resonance (FMR) method reveals perpendicular magnetic anisotropy in fabricated films. Angular measurements of FMR give the constants of uniaxial and cubic anisotropy in BIG film: Ku = 5.9×104 erg/cm3 and K1= - 6.95×103 erg/cm3. The Faraday rotation has been found to reach - 7.8 deg/µm at 630 nm.
Bismuth Pyrochlore Films for Dielectric Applications
Authors: Ren Wei , Thayer Ryan , Randall Clive A. , Shrout Thomas R. , Trolier-McKinstry Susan 
Published: April 2011

AbstractBismuth pyrochlore ceramics have modest temperature coefficients of capacitance, good microwave properties, and can be prepared at relatively modest temperatures (∼900 – 1100 °C). This work focuses on the preparation and characterization of thin films in this family for the first time. A sol-gel procedure using bismuth acetate in acetic acid and pyridine, in combination with zinc acetate dihydrate and niobium ethoxide in 2-methoxyethanol was developed. The solution chemistry was adjusted to prepare (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 and Bi2(Zn1/3Nb2/3)2O7 films. Solutions were spin-coated onto platinized Si substrates and crystallized by rapid thermal annealing. In both cases, crystallization occurred by 550 °C into the cubic pyrochlore structure. (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 films remained in the cubic phase up to crystallization temperatures of 750 °C, while the structure of the Bi2(Zn1/3Nb2/3)2O7 thin films is dependent of the firing temperature: cubic below 650 °C and orthorhombic above 750 °C. A mixture of cubic and orthorhombic structures is found at 700 °C. The resulting BZN films are dense, uniform, and smooth (rms roughness of < 5 nm). Cubic bismuth zinc niobate films show dielectric constants up to 150, a negative temperature coefficient of capacitance, TCC, (∼ - 400 ppm/°C), tan δ < 0.01, and a field tunable dielectric constant. Orthorhombic films showed smaller dielectric constants (∼80), low tan δ (< 0.01), positive TCC, and field independent dielectric constants. TCC could be adjusted to new 0 ppm/°C using a mixture of orthorhombic and cubic material.
Microstructure of YBCO and YBCO/SrTiO3/YBCO PLD Thin Films on Sapphire for Microwave Applications
Authors: Lorenz M. , Hochmuth H. , Natusch D. , Thärigen T. , Svetchnikov V. L. , Zandbergen H. W. , Schäfer C. , Kästner G. , Hesse D. 
Published: April 2011

AbstractA large-area pulsed laser deposition process for high-quality YBa2Cu3O7−δ (YBCO) thin films on both sides of R-plane sapphire substrates with CeO2 buffer layer is used routinely to optimize planar microwave filters for satellite and mobile communication systems. With the experience of more than 700 double-sided 3-inch diam. YBCO:Ag films a high degree of reproducibility of jc values above 3.5 MA/cm2 and of state of the art R5 values is reached. TEM cross sections of the large-area and double-sided PLD-YBCO:Ag thin films on R-plane sapphire with CeO2 buffer layers show typical defects like stress modulation, stacking faults, a-axis oriented grains, precipitates and interdiffusion layers. YBCO films on SrTiO3 / YBCO* / CeO2 film systems on R-plane sapphire wafers have more growth defects compared to bare CeO2 buffers on sapphire but show as microwave resonators encouraging electrical tunability.
MOCVD Growth and Characterization of (BaxSr1−x)Ti1+yO3+z Thin Films for High Frequency Devices
Authors: Baumann P.K. , Kaufman D.Y. , Streiffer S.K. , IM J. , Auciello O. , Erck R.A. , Giumarra J. , Zebrowski J. , Baldo P. , McCormick A. 
Published: April 2011

AbstractWe have investigated the structural and electrical characteristics of (BaxSr1−x)Ti1+yO3+z (BST) thin films. The BST thin films were deposited at 650°C on platinized silicon with good thickness and composition uniformity using a large area, vertical liquid-delivery metalorganic chemical vapor deposition (MOCVD) system. The (Ba+Sr)/Ti ratio of the BST films was varied from 0.96 to 1.05 at a fixed Ba/Sr ratio of 70/30, as determined using x-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). Patterned Pt top electrodes were deposited onto the BST films at 350°C through a shadow mask using electron beam evaporation. Annealing the entire capacitor structure in air at 700°C after deposition of top electrodes resulted in a substantial reduction of the dielectric loss. Useful dielectric tunability as high as 2.3:1 was measured.
Microstructural Architecture of (Ba,Sr)TiO3 Thin Films for Tunable Microwave Applications
Authors: Chang Wontae , Horwitz James S. , Kim Won-Jeong , Gilmore Charles M. , Pond Jeffrey M. , Kirchoefer Steven W. , Chrisey Douglas B. 
Published: April 2011

AbstractBaxSr1−xTiO3 (BST, x=0.5 and 0.6) thin films have been deposited onto (100) MgO single crystal substrates by pulsed laser deposition (PLD). The room temperature capacitance and dielectric quality factor (Q=1/tanδ have been measured as a function of electric field (≤ 100 kV/cm) at microwave frequencies (1 to 20 GHz) using silver interdigitated electrodes deposited on top of the BST film. It has been observed that the dielectric constant of the film and its change with electric field are closely related to film phase (amorphous to crystalline phase) and film strain which affects the ionic polarization of the film. Amorphous BST films show high dielectric Q (> 100) with low dielectric constant (∼30–200) and low dielectric tuning (< 1%), presumably due to small ionic polarization. Crystalline films have a higher dielectric constant (∼1000–3000) and a higher dielectric tuning (∼ 65%) but a lower dielectric Q (∼20). As an optimal microstructure of the film for tunable microwave applications, strain-relieved large-grained (∼5000 Å) randomly oriented polycrystalline films were deposited using a thin amorphous buffer layer of BST (∼50 Å). Very large grains (size up to a few microns) were observed in BST films prepared using a thicker amorphous buffer layer (∼500 Å). We will present results on how careful control of microstructure can lead to films with optimal dielectric properties for the tunable microwave devices.
Role of SrRuO3 Buffer Layers in Enhancing Dielectric Properties of Ba0.5Sr0.5TiO3 Tunable Capacitors
Authors: Park S.J. , Sok J. , Lee E.H. , Lee J.S. 
Published: April 2011

AbstractBaM0.5Sr0.5TiO3 (BST) is a first candidate material for the development of voltage-tunable microwave devices, such as, filter, phase-shifter and VCO. In this work, crystal structures and dielectric properties of BST film are investigated with and without SrRuO3(SRO) buffer layers. BST and SRO thin films are sequentially prepared by pulsed laser deposition and Au/Ti metal electrodes are fabricated by a DC magnetron sputtering system. The capacitance of the capacitors has been measured as a function of bias voltages at room temperature using a low frequency LCR meter. For the high frequency characteristics (∼2GHz), a microstrip resonator with ∼2GHz resonance frequency and the center coupling design is fabricated. Using flip-chip BST capacitor attached at the position of the center coupling on the microstrip resonator, Its dielectric loss and tunability were obtained. The microwave loss was obviously enhanced in the film with SRO buffer layer..
Strain Tuned Magnetic Properties of Epitaxial Cobalt Ferrite Thin Films
Authors: Hu G. , Choi J.H. , Eom C.B. , Suzuki Y. 
Published: April 2011

AbstractEpitaxial cobalt ferrite thin films have been fabricated on bare MgO substrates and compared to those grown on CoCr2O4 buffered MgAl2O4. Various structural characterizations, including x-ray diffraction, Rutherford backscattering spectroscopy and transmission electron microscopy, demonstrate excellent crystallinity of the films. Films grown under tension exhibit magnetic properties dominated by the stress anisotropy. In (110) oriented films grown on CoCr2O4 buffered MgAl2O4, post deposition annealing switched the in-plane easy and hard directions completely while no such behavior is observed in cobalt ferrite films grown on MgO. The anomalous behaviors observed in as-grown films and films after annealing can be explained in terms of lattice distortion and cation redistribution.
Local Optical Probes of Microwave Dielectric Dispersion in Ferroelectric Thin Films
Authors: Hubert Charles , Levy Jeremy , Cukauskas E. J. , Kirchoefer Steven W. , Pond Jeffrey M. , DeSisto William J. 
Published: April 2011

AbstractThe soft-mode contribution to the dielectric response of Ba0.5Sr0.5TiO3 ferroelectric thin films is measured locally at microwave frequencies using time-resolved confocal scanning optical microscopy. Optical measurements performed on an ensemble of nanometer-scale regions show a well-defined phase shift between the paraelectric and ferroelectric response at 2-4 GHz. Application of a static electric field produces large local variations in the phase of the ferroelectric response. These variations are attributed to the growth of a-axis ferroelectric nanodomains whose size-dependent relaxation frequencies lead to strong dielectric dispersion at mesoscopic scales. The in-plane paraelectric response is believed to arise from the surrounding c-axis matrix and non-polar regions, and shows negligible dispersion. These results provide a direct view of the soft-mode mechanisms of microwave dielectric loss in ferroelectric thin films.
RF-Magnetron Sputtered Strontium Titanate: Structure, Processing and Property Relationships
Authors: Gibbons B.J. , Fan Y. , Findikoglu A.T. , Reagor D.W. , Jia Q.X. 
Published: April 2011

AbstractThe low frequency dielectric properties of epitaxial SrTiO3 thin films deposited on LaAlO3 are presented. The films were deposited using radio-frequency magnetron sputtering from stoichiometric targets in an Ar/O2 atmosphere. For the first time, the effects of in situ ozone annealing during the early stages of deposition were explored. X-ray diffraction results indicated that the ozone treatment resulted in more symmetric and sharper diffraction peaks (2 Θ- FWHM decreased from 0.17° to 0.10°). In addition, the peaks for the ozone treated samples were shifted in 2 Θ towards values approaching the bulk value. Rutherford backscattering measurements showed Sr/Ti ratios of 1:1 for these samples, indicating these peak shifts are not due to compositional variations. The dielectric constant of the ozone treated samples increased from 275 at room temperature to 1175 at 22 K (measured at 100 kHz). The effective loss tangent of the device remained between 1 × 10−4 and 1 × 10−3 down to 100 K, where it began to increase. The tunability was also measured. The ozone treated sample showed tunability of 46%, 43% and 38% at 22 K, 40 K and 60 K, respectively. Finally, similar measurements were completed at 1 MHz, indicating a minimal dependence of these properties on frequencies in this range.
Materials Issues in the Application of Ferromagnetic Films in Tunable High Q VHF/UHF Devices
Authors: Walser R.M. , Valanju A. P. , Win W. 
Published: April 2011

AbstractThin ferromagnetic films have narrow ferromagnetic resonance bandwidths, and large RF permeabilities that are attractive for tunable high Q device applications. They can also be processed at low temperatures and integrated with most RF and microwave materials. At VHF/UHF frequencies, where discrete devices can be realized, magnetic loss tangents (Q−1) less than 10−3 can be obtained, if the effects of spin resonance and eddy current losses are reduced. The material figure of merit requires a tradeoff of the permeability, and Q. The highest FOM is obtained by maximizing the magnetization, anisotropy, resistivity, and minimizing the magnetic loss. This paper discusses the interplay of these properties, and the fill factor and magnetic bias required for tunable inductors with Q>1000 in the ∼50-500 MHz range. The most promising candidates for these applications are shown to be reactively sputtered nanocrystalline films. The large resistivity, magnetization, and thickness of these films can be used to attain large film permeances, and increased shape anisotropy fields from patterned film objects. The latter eliminates the need for using a large bias magnet to achieve Q's ∼1000 at VHF/UHF operating frequencies.
Study of Vacancy and Impurity Complexes in Si Solid-Phase Epitaxial Crystallization with Positron Annihilation Spectroscopy
Authors: Chen Claudine M. , Rassiga Stefano , Weber Marc H. , Petkov Mihail P. , Lynn Kelvin G. , Atwater Harry A. 
Published: April 2011

AbstractWe investigate the residual vacancy defect species after crystallization of amorphous Si (a-Si) by solid phase epitaxy (SPE). To this end, we correlate the total and electronically-active doping concentrations measured by secondary mass spectrometry and spreading resistance analysis, and data from positron annihilation spectroscopy (PAS), which is sensitive to openvolume defects. Float-zone silicon substrates were implanted with boron, phosphorus and both phosphorus and boron ions to create nonuniform doping profiles at degenerate doping levels, after an amorphization step by 29Si+ ions. Samples were vacuum annealed at 600°C to induce SPE, and the SPE rate was measured by time-resolved reflectivity. PAS was used for identification of the impurity-defect complexes. Momentum-resolved PAS measurements enable the detection of phosphorus-vacancy (P-V) and oxygen-vacancy (O-V) complexes.
Atomistic Modeling of Complex Silicon Processing Scenarios
Authors: Jaraiz Martin , Castrillo Pedro , Pinacho Ruth , Pelaz Lourdes , Barbolla Juan , Gilmer George H. , Rafferty Conor S. 
Published: April 2011

AbstractThe level of sophistication reached by today's Si device fabrication technologies has called for new modeling and simulation schemes, capable of handling the wide variety of interaction mechanisms that govern the complex phenomena that can occur at the atomic level. The kinetic Monte Carlo (KMC) technique seems particularly apt for this task. It takes as input basic materials parameters, derived from ab-initio calculations or from experiments, and is capable of carrying out a detailed simulation up to the dimensions and time scales of current ULSI Si device manufacture. In addition, it can accommodate and efficiently simulate complex interactions between multiple dopant and defect types. We explain the approach and show examples of application in both materials processing and device fabrication. Finally, we present the use of some artificial intelligence techniques (namely, genetic algorithms) that look most promising as methodologies that can easy and efficiently be employed to build the extensive KMC parameter database.
Monte Carlo Analysis of the Evolution from Point to Extended Interstitial Type Defects in Crystalline Silicon
Authors: Magna Antonino La , Coffa Salvatore , Libertino Sebania 
Published: April 2011

AbstractWe present a Lattice Kinetic Monte Carlo study of the atomic evolution leading to {311} defects formation upon annealing of a damaged Si-crystal. Self-interstitial (I) agglomeration is modeled by using local interaction and considering the energetic cost to under/over coordinate the Si atoms belonging to an I-complex. The static properties of the I aggregates as derived by molecular dynamics calculations, in the two extreme regimes of very small and very large clusters, have been mapped in the model. The typical evolution of an excess of Si ions is characterized by three distinct stages: (1) the formation of clusters consisting of few interstitials in a over-coordination state, (2) their redistribution in larger agglomerates containing a few of these small I clusters all preserving their original structure, (3) a transition leading to Is rearrangement along the ≪110> chains, which are the structural units of {311} defects. The duration of the preliminary stages critically depends on temperature and density of the added atoms.