Magnetic Behavior in Nanocrystalline Fe-Cu-Nb-Si-B Alloys at Elevated Temperatures

1995 ◽  
pp. 309-316 ◽  
Author(s):  
I. Škorvánek ◽  
C. K. Kim ◽  
R. C. O’Handley
Keyword(s):  
Elevated Temperatures ◽  
Magnetic Behavior

scholarly journals Synthesis of NiFe2O4 nanofibers by joint sol-gel and electrospinning technique

10.30544/387 ◽  
2018 ◽  
Vol 24 (3) ◽  
pp. 173-180
Author(s):  
Aleksandar Grujić ◽  
Vladan Ćosović ◽  
Jasna Stajić-Trošić ◽  
Aleksandar Ćosović ◽  
Mirko Stijepović ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Sol Gel ◽  
Morphological Characteristics ◽  
Magnetic Behavior ◽  
Composition Analysis ◽  
X Ray Diffraction ◽  
Electrospinning Technique ◽  
Web Structure ◽  
Crystallite Sizes ◽  
Ft Ir

In this study, electrospinning combined with sol-gel technique is applied in order to produce magnetic nickel ferrite (Ni-ferrite) nanofibers. The prepared Ni-ferrite gel was mixed with poly(vinylpyrrolidone) (PVP) solution which was used as a spinning aid to enable spinnability of the mixture. Structural and morphological characteristics of the as-spun ferrite gel/PVP composite web structure and calcinated Ni-ferrite nanofibers were analyzed using scanning electron microscopy (SEM). Phase composition analysis was carried out by Fourier-transform infrared (FT-IR) spectroscopy, X-Ray diffraction analysis (XRD) and 57Fe Mössbauer spectroscopy (MS). The obtained results suggest that the pure nanocrystalline NiFe2O4 dense mat to the almost coral-like structure of fibers with diameters ranging from hundreds of nanometers to few micrometers was obtained. The results of MS analysis revealed the existence of a crystallite size distribution within the material as well as the existence of a superparamagnetic fraction with very small crystallite sizes (<13nm). Magnetic behavior of the obtained material at elevated temperatures was also scrutinized using thermomagnetic measurements (TM) up to 800 °C.

Magnetic Behavior of Nanocomposites Prepared in a Vitreous Alumina Gel

1990 ◽  
Vol 206 ◽  
Author(s):  
R. D. Shull ◽  
J. J. Ritter ◽  
A. J. Shapiro ◽  
L. J. Swartzendruber ◽  
L. H. Bennett
Keyword(s):  
Magnetic Susceptibility ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Bulk Material ◽  
Magnetic Behavior ◽  
Subsequent Treatment ◽  
Ferric Nitrate ◽  
Fe Content ◽  
Alumina Gel ◽  
Aqueous Aluminum

ABSTRACTHomogeneous gelled composites of iron and vitreous alumina containing 10-40% Fe have been prepared by room temperature polymerization of aqueous aluminum alkoxide solutions containing ferric nitrate and nitric acid at low pH. Scanning electron microscopy, x-ray diffraction, and Mossbauer spectroscopy demonstrated that this bulk material is comprised of nanometer-sized regions of iron compounds embedded in a vitreous alumina gel matrix. Magnetization data showed that in the as-cured condition these nanocomposites are paramagnetic at room temperature and become either superparamagnetic or ferromagnetic on cooling to 10 K. The magnetic susceptibility increased with the Fe content and with decreasing temperature. Analysis of the temperature dependence of the magnetic susceptibility indicated the magnetic moment per Fe atom was 1.87 µB for the 10% Fe nanocomposite and that it increased linearly with composition to 1.96 µB for the 40% Fe material. Mössbauer effect data showed that subsequent treatment of these materials in a gaseous environment of hydrogen at elevated temperatures (T<400 C) changed the form of the iron in the magnetic regions. These results are compared to that observed for similar nanocomposites prepared using a silica gel matrix.

scholarly journals Peculiar Magnetic Features and Superconductivity in Sulfur Doped Amorphous Carbon

2016 ◽  
Author(s):  
Israel Felner
Keyword(s):  
Amorphous Carbon ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Magnetic Behavior ◽  
Protective Atmosphere ◽  
Zero Field ◽  
Magnetic Studies ◽  
High Tc ◽  
Two Phases ◽  
Magnetic States

We report on magnetic studies of inhomogeneous commercial and synthesized amorphous carbon (a-C) and a-C doped with sulfur (a-CS) powders which exhibit (i) peculiar magnetic behavior and (ii) traces of two superconducting (SC) phase ~ Tc=33 and at 65 K. (i) The temperature dependence of zero-field-cooled (ZFC) curves measured up to room temperature show a well distinguish elusive peaks around 50-80 K, their origin is not yet known. These peaks are totally washed-out in the second ZFC sweeps and in the FC branches as well. As a result, in the vicinity of the peaks, the FC curves lie below the ZFC peaks (FC&lt;ZFC), a phenomenon which is rarely observed. These magnetic anomalies are intrinsic properties of a-C and a-CS materials (ii) SC was observed in three different a-C sources: (a) The commercial a-C powder contains 0.21% of sulfur and it is suggested that two different a-CS phases (at 33 and 65 K) are the origin of the two SC states observed. The compositions of these two phases are not yet unknown. The small SC volume fractions of the 33 K phase can be enhanced by a solid reaction with additional sulfur at 250 &ordm;C. (b) The synthesized a-C powder (obtained from decomposition of sucrose) is not SC. However, when mixed with sulfur and heated at 400 &ordm;C under a protective atmosphere, the a-CS powder obtained also show traces of a SC phase at TC= 42 K. (c)The same occurs in a-C thin films. The as-grown films are not SC but a SC phase at Tc = 34 K emerges after the films were reacted with sulfur at elevated temperatures. It is concluded therefore, that all SC phases observed are due to different unknown a-CS phases. Since the a-C and a-CS powders possess SC and magnetic states, we believe that these powders resemble the high TC curates and Fe-As based systems in which the SC and the magnetic states are closed related to each other.

Epitaxial Growth of Dilute Magnetic Semiconductors: GaMnN and GaMnP

2001 ◽  
Vol 674 ◽  
Author(s):  
Mark E. Overberg ◽  
Cammy R. Abernathy ◽  
Stephen J. Pearton ◽  
Fred Sharifi ◽  
Arthur F. Hebard ◽  
...  
Keyword(s):  
Epitaxial Growth ◽  
Elevated Temperatures ◽  
Magnetic Semiconductors ◽  
Dilute Magnetic Semiconductors ◽  
Chemical Vapor ◽  
Magnetic Behavior ◽  
Organic Chemical ◽  
Preferential Formation ◽  
Metal Organic ◽  
Second Phases

ABSTRACTEpitaxial growth of the dilute magnetic semiconductors GaMnP and GaMnN has been investigated by Gas Source Molecular Beam Epitaxy (GSMBE). GaMnP films grown with < 4.5% Mn show the preferential formation of the second phases MnP and Mn5.64P3, resulting in only a slight deviation from purely diamagnetic behavior. GaMnN films grown on both Al2O3 and Metal-Organic Chemical Vapor Deposition (MOCVD) derived GaN surfaces show strong ferromagnetism when grown with either C codoping or at elevated temperatures to raise the concentration of n-type carriers. Comparable GaMnN films grown under conditions which produce highly resistive material show only paramagnetism, indicating the importance of carrier concentration on the resulting magnetic behavior. The formation of second phases was not observed in the GaMnN material for Mn concentrations less than 9%.

Interfacial Exchange Coupling and the magnetization of Iron Oxide/Nickel Oxide Superlattices

1993 ◽  
Vol 313 ◽  
Author(s):  
S. D. Berry ◽  
D. M. Lind ◽  
E. Lochner ◽  
K. A. Shaw ◽  
D. Hilton ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Exchange Coupling ◽  
Elevated Temperatures ◽  
Magnetic Behavior ◽  
Neel Temperature ◽  
Néel Temperature ◽  
High Crystalline Quality ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

ABSTRACTThe role of interfacial exchange coupling in the magnetic behavior of metal oxide materials has been investigated through the study of Fe3O4/NiO superlattices. We report results on a series of superlattices grown where one bilayer constituent was held to a fixed thickness while varying the other from single unit cell dimensions upward. High crystalline quality was confirmed by XRD, RHEED and neutron diffraction. Magnetization profiles show substantial deviations from bulklike iron oxide results, with an increase in domain rotation energies observed in the superlattices over that of bulk iron oxide (increasing with NiO layer thickness) indicating the strong nature of Fe3O4/NiO interfacial linkage. Neutron scattering at elevated temperatures shows that the NiO remains ordered above the 523 K bulk Néel temperature. This suggests that at least a portion of the NiO within a layer remains ordered well above the Néel temperature, with an increase in effective Néel transition temperature that approaches the Fe3O4 Curie temperature in the limit of very thin NiO layers. Although the exchange coupling dominates these effects, strain also plays an important role.

Characterization of Rare-Earth Fluoride Anti-Stokes Phosphors by Scanning arid Transmission Electron Microscopy

1971 ◽  
Vol 29 ◽  
pp. 142-143
Author(s):  
N. M. P. Low ◽  
L. E. Brosselard
Keyword(s):  
Electron Microscopy ◽  
Rare Earth ◽  
Elevated Temperatures ◽  
Stoichiometric Composition ◽  
Rare Earth Ions ◽  
Crystalline Solid ◽  
Precipitation Process ◽  
Rare Earth Fluoride ◽  
Earth Fluoride ◽  
Rare Earth Fluorides

There has been considerable interest over the past several years in materials capable of converting infrared radiation to visible light by means of sequential excitation in two or more steps. Several rare-earth trifluorides (LaF3, YF3, GdF3, and LuF3) containing a small amount of other trivalent rare-earth ions (Yb3+ and Er3+, or Ho3+, or Tm3+) have been found to exhibit such phenomenon. The methods of preparation of these rare-earth fluorides in the crystalline solid form generally involve a co-precipitation process and a subsequent solid state reaction at elevated temperatures. This investigation was undertaken to examine the morphological features of both the precipitated and the thermally treated fluoride powders by both transmission and scanning electron microscopy.Rare-earth oxides of stoichiometric composition were dissolved in nitric acid and the mixed rare-earth fluoride was then coprecipitated out as fine granules by the addition of excess hydrofluoric acid. The precipitated rare-earth fluorides were washed with water, separated from the aqueous solution, and oven-dried.

Observations oh Nucleation and Growth of Voids in Nickel

1970 ◽  
Vol 28 ◽  
pp. 414-415
Author(s):  
J. L. Brimhall ◽  
H. E. Kissinger ◽  
B. Mastel
Keyword(s):  
High Purity ◽  
Growth Stage ◽  
Elevated Temperatures ◽  
Early Growth ◽  
Nucleation And Growth ◽  
Pure Nickel ◽  
Different Temperatures ◽  
Total Fluence ◽  
Neutron Exposure ◽  
Growth Of Voids

Some information on the size and density of voids that develop in several high purity metals and alloys during irradiation with neutrons at elevated temperatures has been reported as a function of irradiation parameters. An area of particular interest is the nucleation and early growth stage of voids. It is the purpose of this paper to describe the microstructure in high purity nickel after irradiation to a very low but constant neutron exposure at three different temperatures.Annealed specimens of 99-997% pure nickel in the form of foils 75μ thick were irradiated in a capsule to a total fluence of 2.2 × 1019 n/cm2 (E > 1.0 MeV). The capsule consisted of three temperature zones maintained by heaters and monitored by thermocouples at 350, 400, and 450°C, respectively. The temperature was automatically dropped to 60°C while the reactor was down.

Voids in Irradiated Tungsten and Molybdenum

1969 ◽  
Vol 27 ◽  
pp. 190-191
Author(s):  
Robert C. Rau ◽  
Robert L. Ladd
Keyword(s):  
Melting Point ◽  
Fast Neutron ◽  
Neutron Irradiation ◽  
Elevated Temperatures ◽  
Irradiation Temperature ◽  
The Body ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
Face Centered

Recent studies have shown the presence of voids in several face-centered cubic metals after neutron irradiation at elevated temperatures. These voids were found when the irradiation temperature was above 0.3 Tm where Tm is the absolute melting point, and were ascribed to the agglomeration of lattice vacancies resulting from fast neutron generated displacement cascades. The present paper reports the existence of similar voids in the body-centered cubic metals tungsten and molybdenum.

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