The magnetic characteristics of iron oxide nanopowder (Fe
3
O
4
base phase) produced by electroerosion dispersion and consolidated at high pressures (2 GPa) and high temperatures (900, 1000, 1100, ...1200, and 1300°C) for 0.07 h in contact with hexagonal boron nitride were studied. The nanopowder was produced by dispersing iron granules or shavings in plasma induced at contact points between the granules when electric pulses of high current and voltage were passed through them. The metal granules being dispersed are in a constantly circulating liquid (water) atmosphere, creating a pseudo-boiling layer from the granules. The liquid (water in this case) cools the granules to prevent them from being welded and oxidizes the metal vapors that emerge in plasma, forming nanosized iron oxide grains carried by the liquid flow into sedimentation tanks (powders with different grain sizes sediment in different tanks). Room-temperature studies of the magnetic characteristics of samples consolidated from iron oxide powders showed that the materials sintered at 1200 and 1300°C were soft magnetics with virtually zero hysteresis. Their specific magnetic moments at 5000 Oe were 128.4 and 126.4 emu/g and the coercive force was negligibly small: 5.1 and 4.5 Oe. The materials sintered at 1100°C were characterized by a specific magnetic moment of 90.4 emu/g and a relatively low coercive force of 9.1 Oe. The specific magnetic moments of the samples sintered at 900 and 1000°C were significantly lower and the coercive force higher: 40.2 and 42.1 emu/g and 37.9 and 32.4 Oe, respectively. X-ray diffraction with Rietveld refinement revealed that the materials consolidated at 900 and 1000°C contained 75–80 wt.% FeO and 25–20 wt.% Fe, while the materials sintered at 1100°C contained, along with 32 wt.% FeO and 2 wt.% Fe, a significant amount of Fe
3
N (66 wt.%). The materials consolidated at 1200–1300°C contained 100% Fe
3
N phase. Hence, under high pressures and increasing sintering temperatures, iron oxides are reduced and then iron is nitrided with nitrogen released from boron nitride, which improves the soft magnetic characteristics of the sintered materials.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The oxygen concentration and distribution in the microstructure of MgB 2 - and YBa 2 Cu 3 O 7-δ -based materials affect the formation of nanostructural defects and thus influence the critical current ...density, upper critical magnetic field and irreversibility field. For MgB 2 oxygen containing additions (Dy-O, Ti-O) in the form of nanograins occurred not to be very effective for an increase of critical current density, j c . Sn-O additions to MgB 2 can provoke even a significant decrease of j c due to a chemical interaction of Sn with MgB 2 . The processing pressure and temperature influence the defect density of the relevant pinning centers and the regularity of their distribution in doped and undoped MgB 2 as well as in MT-YBCO.
Abstract
Measurements of the microwave surface impedance for high-temperature superconductor YBa
2
Cu
3
O
7−
x
(YBCO) films irradiated by 3 MeV Au
2+
ions at three irradiation doses (10
10
cm
−2
, 10
...11
cm
−2
, and 10
12
cm
−2
) were carried out at different temperatures (below the critical temperature of
T
с
≈ 90 К) and various rf current amplitudes by the use of the microstrip resonator technique. A noticeable decrease in the surface resistance and an enhancement of the linear response range at low temperatures were observed for moderately irradiated film exposed to an irradiation dose of 10
11
cm
−2
, while at higher irradiation doses (10
12
cm
−2
) an increase in the surface resistance and a decrease in the linear response range were observed for all temperatures below
T
c
. These results are discussed in the framework of phenomenological theory for the microwave response of superconductors with nano-sized structural defects.
The Josephson effect in the array of superconducting nano-bridges (short circuits) connected in parallel within the intermediate semiconductor layer with metallic (M) nanoclusters (Sm(M)), separating ...two superconducting plates (S) in the presence of applied parallel dc magnetic field is considered basing on the generalized Ferrell–Prange model. This model seems to be relevant for understanding of the unusual Josephson critical current dependence, Ic(H), on applied parallel magnetic field in a S-Sm(M)-S type planar Josephson junction (MoRe–Si(W)–MoRe). Lack of the typical Fraunhofer type Ic(H) dependence for this type Josephson junctions is related with a discrete Josephson current flow through the set of parallel metallic nanobridges (or resonant-percolation trajectories) formed by M-nanoclusters within the semiconductor (Sm)-intermediate layer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The critical current density at 4.2 and 20 K up to 15 T and the temperature dependence of the irreversible field have been studied in magnesium diboride wires and bulks prepared from boron without ...and with carbon addition. Structural investigations using X-ray microprobe analysis have been performed. A monofilamentary wire with a round-shaped core manufactured from boron containing 2 mol.% carbon (approximate composition of its matrix MgB 1.8-2.4 O 0.04-0.71 C 0.12-0.16 ) demonstrated J c (20 K, 2 T) = 10 5 A/cm 2 , J c (4.2 K, 15 T) = 2 × 10 3 A/cm 2 and B irr (20 K) = 8 T, B irr (12.5 K) = 15 T. Bulk material synthesized at 2 GPa, 600 °C, 1 h from carbon doped boron demonstrated J c (10 K, 10 T) = 4 × 10 3 A/cm 2 and J c (20 K, 6 T) = 4 × 10 3 A/cm 2 .
Preparation and Properties of MgB2 Thin Films Prikhna, Tatiana A.; Eisterer, Michael; Shaternik, Anton V. ...
IEEE transactions on applied superconductivity,
10/2018, Volume:
28, Issue:
7
Journal Article
Peer reviewed
The superconducting transition temperature of 140 nm ± 10 nm thin films on sapphire substrates, which were deposited by magnetron sputtering, was around 36 K. Using a magnetization technique, the ...film's critical current density was estimated as J C = 1.8 × 10 7 A/cm 2 at 10 K, J C = 8 × 10 6 A/m 2 at 20 K in a zero magnetic field B, and J C = 3 × 10 6 A/m 2 at 10 K and B = 5 T. The values of the upper critical magnetic field B c2 and the irreversibility field B irr estimated using the four-probe technique were B C2 (22 K) = 15 T when H||film surface, 11 T when H⊥film surface, and B irr (22 K) = 11 T when H||film surface. The X-ray study showed that the microstructure of the film contains only MgB 2 and MgO (in minority). The SEM and EPXMA study and quantitative Auger spectroscopy analysis revealed periodical variations of the film composition on the nanolevel and the presence of (mainly) two intercalated Mg-B-O-C phases of slightly different, especially in oxygen content, and thus with different conductivity and, possibly, with different T C . The characteristics of superconducting magnesium diboride films make them promising for application in electronic devices, e.g., as high-pass filters.
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