scholarly journals Vortex Dynamics and Instabilities in Tax Ge1-x/Ge Multilayers

2021 ◽  
Author(s):  
◽  
Benjamin John Ruck
Keyword(s):  
High Vacuum ◽  
Qualitative Difference ◽  
Activation Energies ◽  
Valuable Insight ◽  
Zero Field ◽  
Type Ii ◽  
Finite Sample ◽  
Critical Fields ◽  
Individual Layer ◽  
Fluctuation Conductivity

<p>In this thesis the magnetic response of a layered type-II superconducting system is explored across the entire range of fields, temperatures and currents where superconductivity exists, with the results providing valuable insight into the role of reduced dimensionality in determining the behaviour of type-II materials such as the new high temperature superconductors. The system in question consists of alternating layers of amorphous Ta or TaxGe1-x (x approximation 0.3) with amorphous Ge where the individual layer thicknesses vary between 17A [angstrom] and 210A [angstrom]. These multilayers were fabricated by vapour deposition in a high vacuum chamber which allowed the creation of samples with uniform layers of high purity. The resistive transport properties have been measured from Tc (approximation 1-3K) to temperatures as low as 50mK in some cases, and in fields of up to 15T. The upper critical fields have been determined from the fluctuation conductivity both with the field parallel and perpendicular to the layer plane of the samples. The results show clearly the dependence of the dimensionality on the superconducting layer thickness and the degree of coupling across the Ge layers. For the samples with the most two-dimensional properties the zero field resistive transition is governed by the unbinding of thermally created vortex-antivortex pairs as described by the Berezinskii-Kosterlitz-Thouless theory. A detailed investigation of the perpendicular field vortex states and dynamics has been performed, including measurement of the activation energies needed for thermally activated vortex motion. Qualitative difference are observed between the activation energies in two- and three-dimensional samples, with the barriers being generally higher in 3D. The non-linear current-voltage characteristics of the samples provide evidence for the existence of a vortex glass state which melts into a liquid below Hc2, although the divergence of the activation barriers in the glass can be restricted by the finite sample thickness. A brief investigation of the corresponding parallel field regime showed considerably less dissipation, due largely to the transparent nature of the Ge layers to the magnetic field. At the highest currents an instability is observed in the vortices which can drive the samples discontinuously back into the normal state. This instability is shown to be of the type predicted by Larkin and Ovchinnikov (LO), including quantitative agreement between the measured and predicted values of the critical vortex velocity. Several features of the instability are noted which are not specifically predicted by the LO theory, and comparisons are drawn between these and the prevailing vortex state at lower currents.</p>

scholarly journals Vortex Dynamics and Instabilities in Tax Ge1-x/Ge Multilayers

2021 ◽  
Author(s):  
◽  
Benjamin John Ruck
Keyword(s):  
High Vacuum ◽  
Qualitative Difference ◽  
Activation Energies ◽  
Valuable Insight ◽  
Zero Field ◽  
Type Ii ◽  
Finite Sample ◽  
Critical Fields ◽  
Individual Layer ◽  
Fluctuation Conductivity

<p>In this thesis the magnetic response of a layered type-II superconducting system is explored across the entire range of fields, temperatures and currents where superconductivity exists, with the results providing valuable insight into the role of reduced dimensionality in determining the behaviour of type-II materials such as the new high temperature superconductors. The system in question consists of alternating layers of amorphous Ta or TaxGe1-x (x approximation 0.3) with amorphous Ge where the individual layer thicknesses vary between 17A [angstrom] and 210A [angstrom]. These multilayers were fabricated by vapour deposition in a high vacuum chamber which allowed the creation of samples with uniform layers of high purity. The resistive transport properties have been measured from Tc (approximation 1-3K) to temperatures as low as 50mK in some cases, and in fields of up to 15T. The upper critical fields have been determined from the fluctuation conductivity both with the field parallel and perpendicular to the layer plane of the samples. The results show clearly the dependence of the dimensionality on the superconducting layer thickness and the degree of coupling across the Ge layers. For the samples with the most two-dimensional properties the zero field resistive transition is governed by the unbinding of thermally created vortex-antivortex pairs as described by the Berezinskii-Kosterlitz-Thouless theory. A detailed investigation of the perpendicular field vortex states and dynamics has been performed, including measurement of the activation energies needed for thermally activated vortex motion. Qualitative difference are observed between the activation energies in two- and three-dimensional samples, with the barriers being generally higher in 3D. The non-linear current-voltage characteristics of the samples provide evidence for the existence of a vortex glass state which melts into a liquid below Hc2, although the divergence of the activation barriers in the glass can be restricted by the finite sample thickness. A brief investigation of the corresponding parallel field regime showed considerably less dissipation, due largely to the transparent nature of the Ge layers to the magnetic field. At the highest currents an instability is observed in the vortices which can drive the samples discontinuously back into the normal state. This instability is shown to be of the type predicted by Larkin and Ovchinnikov (LO), including quantitative agreement between the measured and predicted values of the critical vortex velocity. Several features of the instability are noted which are not specifically predicted by the LO theory, and comparisons are drawn between these and the prevailing vortex state at lower currents.</p>

Estimation of P(X

2017 ◽  
Vol 34 (7) ◽  
pp. 1111-1122 ◽  
Author(s):  
Soumya Roy ◽  
Biswabrata Pradhan ◽  
E.V. Gijo
Keyword(s):  
Maximum Likelihood ◽  
Censored Data ◽  
Quality Characteristic ◽  
Logistic Distribution ◽  
Type Ii ◽  
Finite Sample ◽  
Data Set ◽  
Content Type ◽  
Type Ii Censored Data ◽  
Interval Estimators

Purpose The purpose of this paper is to compare various methods of estimation of P(X<Y) based on Type-II censored data, where X and Y represent a quality characteristic of interest for two groups. Design/methodology/approach This paper assumes that both X and Y are independently distributed generalized half logistic random variables. The maximum likelihood estimator and the uniformly minimum variance unbiased estimator of R are obtained based on Type-II censored data. An exact 95 percent maximum likelihood estimate-based confidence interval for R is also provided. Next, various Bayesian point and interval estimators are obtained using both the subjective and non-informative priors. A real life data set is analyzed for illustration. Findings The performance of various point and interval estimators is judged through a detailed simulation study. The finite sample properties of the estimators are found to be satisfactory. It is observed that the posterior mean marginally outperform other estimators with respect to the mean squared error even under the non-informative prior. Originality/value The proposed methodology can be used for comparing two groups with respect to a suitable quality characteristic of interest. It can also be applied for estimation of the stress-strength reliability, which is of particular interest to the reliability engineers.

Localizing the Source of Type II Emission Around a CME with the Sun Radio Interferometer Space Experiment (SunRISE) and MHD Simulations

2021 ◽  
Author(s):  
Alexander Hegedus ◽  
Ward Manchester ◽  
Justin Kasper ◽  
Joseph Lazio ◽  
Andrew Romero-Wolf
Keyword(s):  
Data Processing ◽  
Low Frequency ◽  
Solar Energetic Particle ◽  
Radio Interferometer ◽  
Valuable Insight ◽  
Type Ii ◽  
Plasma Parameters ◽  
Low Frequencies ◽  
The Earth ◽  
Type Ii Bursts

&lt;p&gt;The Earth&amp;#8217;s Ionosphere limits radio measurements on its surface, blocking out any radiation below 10 MHz. Valuable insight into many astrophysical processes could be gained by having a radio interferometer in space to image the low frequency window, which has never been achieved. One application for such a system is observing type II bursts that track solar energetic particle acceleration occurring at Coronal Mass Ejection (CME)-driven shocks. This is one of the primary science targets for SunRISE, a 6 CubeSat interferometer to circle the Earth in a GEO graveyard orbit. SunRISE is a NASA Heliophysics Mission of Opportunity that began Phase B (Formulation) in June 2020, and plans to launch for a 12-month mission in mid-2023. In this work we present an update to the data processing and science analysis pipeline for SunRISE and evaluate its performance in localizing type II bursts around a simulated CME.&lt;/p&gt;&lt;p&gt;To create realistic virtual type II input data, we employ a 2-temperature MHD simulation of the May 13th 2005 CME event, and superimpose realistic radio emission models on the CME-driven shock front, and propagate the signal through the simulated array. Data cuts based on different plasma parameter thresholds (e.g. de Hoffman-Teller velocity and angle between shock normal and the upstream magnetic field) are tested to get the best match to the true recorded emission. &amp;#160;This model type II emission is then fed to the SunRISE data processing pipeline to ensure that the array can localize the emission. We include realistic thermal noise dominated by the galactic background at these low frequencies, as well as new sources of phase noise from positional uncertainty of each spacecraft. We test simulated trajectories of SunRISE and image what the array recovers, comparing it to the virtual input, finding that SunRISE can resolve the source of type II emission to within its prescribed goal of 1/3 the CME width. This shows that SunRISE will significantly advance the scientific community&amp;#8217;s understanding of type II burst generation, and consequently, acceleration of solar energetic particles at CMEs.&amp;#160; This unique combination of SunRISE observations and MHD recreations of space weather events will allow an unprecedented look into the plasma parameters important for these processes.&amp;#160;&lt;/p&gt;

scholarly journals Phase Formation and High-Temperature Stability of Very Thin Co-Sputtered Ti-Al and Multilayered Ti/Al Films on Thermally Oxidized Si Substrates

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2039
Author(s):  
Marietta Seifert ◽  
Eric Lattner ◽  
Siegfried B. Menzel ◽  
Steffen Oswald ◽  
Thomas Gemming
Keyword(s):  
Phase Formation ◽  
Photoelectron Spectroscopy ◽  
High Vacuum ◽  
Ambient Atmosphere ◽  
High Temperature Stability ◽  
Individual Layer ◽  
Cover Layer ◽  
X Ray ◽  
Si Substrates ◽  
20 Nm

Ti-Al thin films with a thickness of 200 nm were prepared either by co-sputtering from elemental Ti and Al targets or as Ti/Al multilayers with 10 and 20 nm individual layer thickness on thermally oxidized Si substrates. Some of the films were covered with a 20-nm-thick SiO 2 layer, which was used as an oxidation protection against the ambient atmosphere. The films were annealed at up to 800 °C in high vacuum for 10 h, and the phase formation as well as the film architecture was analyzed by X-ray diffraction, cross section, and transmission electron microscopy, as well as Auger electron and X-ray photoelectron spectroscopy. The results reveal that the co-sputtered films remained amorphous after annealing at 600 °C independent on the presence of the SiO 2 cover layer. In contrast to this, the γ -TiAl phase was formed in the multilayer films at this temperature. After annealing at 800 °C, all films were degraded completely despite the presence of the cover layer. In addition, a strong chemical reaction between the Ti and SiO 2 of the cover layer and the substrate took place, resulting in the formation of Ti silicide. In the multilayer samples, this reaction already started at 600 °C.

Magnetic Relaxation in Bi2Sr2Ca1Cu2O8+x Single Crystal

1989 ◽  
Vol 169 ◽  
Author(s):  
E. Agostinelli ◽  
G. Balestrino ◽  
D. Fiorani ◽  
P. Paroli ◽  
J. Tejada ◽  
...  
Keyword(s):  
Single Crystal ◽  
Magnetic Relaxation ◽  
Remanent Magnetization ◽  
Effective Activation Energy ◽  
Critical Currents ◽  
Activation Energies ◽  
Zero Field ◽  
Time Decay ◽  
Effective Activation ◽  
Flux Motion

AbstractThe results of measurements of critical currents and magnetic relaxation on a Bi2 Sr2 Ca1 Cu2O8+x single crystal are reported. Activation energies for the flux motion have been determined from the temperature dependence of the critical current density and the time decay of the zero‐field‐cooled and the remanent magnetization. The effective activation energy increases with temperature, in agreement with the existence of a distribution of activation energies.

Thermionic Emission of Yttrium Dodecaboride Single Crystal

2019 ◽  
Vol 289 ◽  
pp. 47-52 ◽  
Author(s):  
Daniil Voronovych ◽  
Anatoliy Taran ◽  
Oksana Podshyvalova ◽  
Natalya Shitsevalova ◽  
Volodymyr Filipov ◽  
...  
Keyword(s):  
Single Crystal ◽  
Work Function ◽  
Current Density ◽  
Crystal Surface ◽  
High Vacuum ◽  
Electron Work Function ◽  
Linear Functions ◽  
Zero Field ◽  
Effective Electron ◽  
Temperature Dependences

Experimental data on thermionic current density and electron work function of YB12 (100) at T = 1218 – 1978 K in high vacuum (p < 10-4 Pa) are first introduced. Temperature dependences of the thermionic current density and effective electron work function are presented without extrapolation to the zero-field currents because of the anomalous Schottky effect. The temperature dependences of theYB12 electron work function can be described by linear functions at certain temperature intervals. Preferential boron evaporation and additional ion bombardment by the residual gases ions and evaporated boron ions results in appearance of new phases depleted of boron on the YB12 surface. As a result, an YB4 – YB6 double layer on the YB12 single crystal surface has formed. The appearance of the new boride phases, depleted of boron, on the emitting surface causes an increase of thermionic current density compared with individual YB12.

Size Dependent Magnetization and High-Vacuum Annealing Enhanced Ferromagnetism in Zn1−xCoxO Nanowires

2008 ◽  
Vol 8 (1) ◽  
pp. 202-211 ◽  
Author(s):  
Wen-Bin Jian ◽  
I-Jan Chen ◽  
Tai-Ching Liao ◽  
Yi-Ching Ou ◽  
Cheng-Hsun Nien ◽  
...  
Keyword(s):  
Room Temperature ◽  
Spontaneous Magnetization ◽  
Diluted Magnetic Semiconductor ◽  
High Vacuum ◽  
Magnetic Semiconductor ◽  
Hysteresis Loops ◽  
High Energy ◽  
Zero Field ◽  
Nanowire Diameter ◽  
Size Dependent

Diameter controllable ZnO nanowires have been fabricated by thermal evaporation (vapor transport) with various sizes of gold nanoparticles as catalysts. Diluted magnetic semiconductor (DMS) Zn1−xCoxO nanowires were then made by high energy Co ion implantation. The as-implanted and the argon-annealed Zn1−xCoxO nanowires displayed weak ferromagnetism while the high-vacuum annealed nanowires exhibited strong ferromagnetic ordering at room temperature. Size dependent behavior has been observed in the magnetic field and temperature dependences of magnetization. The shrinkage of the nanowire diameter reduced the spontaneous magnetization as well as the hysteresis loops. Field cooled and zero-field cooled magnetization and coercivity measurements were performed between 2 and 300 K to study the evolution of magnetism from the weak to the strong ferromagnetic states. In particular, superparamagnetic features were observed and shown to be intrinsic characteristics of the DMS Zn1−xCoxO nanowires. The room-temperature spontaneous magnetization of individual Zn1−xCoxO nanowires was also established by using magnetic force microscope measurements.

Antiferromagnetism and metamagnetism in 1,4-diazine and pyridine complexes of nickel(II)

1995 ◽  
Vol 73 (2) ◽  
pp. 275-283 ◽  
Author(s):  
Tom Otieno ◽  
Robert C. Thompson
Keyword(s):  
Magnetic Properties ◽  
Electronic Spectroscopy ◽  
Antiferromagnetic Coupling ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Critical Fields ◽  
Scanning Calorimetry ◽  
Magnetic Exchange ◽  
Nickel Ions ◽  
Pyridine Complexes

Several nickel(II) complexes containing pyridine (py), pyrazine (pyz) or methylpyrazine (mepyz) have been synthesized and characterized by vibrational and electronic spectroscopy, differential scanning calorimetry, and magnetic susceptibility studies to cryogenic temperatures. A comparison of the magnetic properties of the polymeric diazine-bridged complexes, Ni(pyz)2X2 (X = Cl or NO3), Ni(pyz)(p-CH3C6H4SO3)2, Ni(mepyz)(NO3)2, and Ni(pyz)3(CH3SO3)2•CH3OH with those of the related monometallic systems, Ni(py)4X2 (X = Cl, p-CH3C6H4SO3 or CH3SO3) and Ni(mepyz)4(NO3)2•H2O provides evidence for weak antiferromagnetic coupling between metal centers mediated by bridging diazine ligands in the former group of compounds. The magnetic properties were analyzed employing a model for S = 1 which takes into account zero-field splitting and employs a molecular field term to account for weak magnetic exchange. The compounds Ni(pyz)Cl2 and Ni(py)Cl2 show metamagnetic behaviour with critical fields of 13 and 2 kOe, respectively, at 2 K. In these compounds nickel ions, linked in chains by bridging chlorides, exhibit intrachain ferromagnetic and interchain antiferromagnetic exchange. In Ni(pyz)Cl2 bridging pyrazine ligands are considered to provide the pathway for the antiferromagnetic coupling resulting in a high critical field. Keywords: nickel(II), pyrazine, pyridine, complexes, metamagnetism, antiferromagnetism.

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