The hysteretic behavior of magnetoresistance
R
(
H
) of the granular high-temperature superconductor (HTS) HoBa
2
Cu
3
O
7 – δ
has been investigated. The YBCO superconductors with a rare-earth ...element (Nd, Ho, Er, Sm, Yb, or Dy) with the magnetic moment in the yttrium site are characterized by a significant paramagnetic contribution to the total magnetization. The main goal of this study has been to establish the possible effect of this paramagnetic contribution on the magnetotransport properties, which are determined by tunneling of superconducting current carriers through the grain boundaries. An analysis of the results obtained basing on the concept of an effective field in the intergrain medium showed that the distribution of the magnetic induction lines from the paramagnetic moments is fundamentally different from that of the Meissner currents and Abrikosov vortices. The magnetic induction lines from the paramagnetic moments are not concentrated in the region of grain boundaries and therefore insignificantly affect the magnetotransport properties of a granular HTS. At the same time, the magnetic induction lines are strongly concentrated in the grain boundaries, which is caused by the Meissner currents and Abrikosov vortices, due to the features of their properties. Specifically, the magnetic flux compression determines the magnetotransport (in particular, the
R
(
H
) hysteresis) properties of granular HTSs, including 1–2–3 ones, with a rare-earth ion with the magnetic moment.
Energy dispersive X-ray spectroscopy and scanning electron microscopy are used to study La
2
CuO
4
–La
1.56
Sr
0.44
CuO
4
composites with different annealing times. Maps of the strontium distribution ...for such systems are calculated and compared to experimental data obtained for the area of contact between two dissimilar granules. The coefficient of lattice diffusion of strontium is found. At the areas of contact between La
2
CuO
4
and La
1.56
Sr
0.44
CuO
4
granules, the strontium concentration corresponds to superconducting phase La
2−
x
Sr
x
CuO
4
with
x
= 0.05–0.25. The technological parameters of synthesis affect the size and number of superconducting and normal regions. Prolonged annealing lowers the gradient of the strontium concentration, which halts the increase in the size of the superconducting regions. This saturation confirms the diffusion front model.
An alternative technique for synthesizing high-temperature superconductor samples is proposed, in which superconducting layers should form on the surface of hard-melting Ho
2
BaCuO
5
green phase ...grains immersed in the liquid phase BaCuO
2
+ CuO.
The superconducting La
1.85
Sr
0.15
CuO
4
ceramics has been studied by small angle neutron scattering, magnetization measurements, and scanning electron microscopy. Experiments have shown that the ...intensity of the magnetic scattering is 2–3 times higher in the field cooled regime than in the zero-field cooled regime. Additional magnetic heterogeneities due to closure of the trapped magnetic flux cause the excess scattering in the field cooled regime. The isotropic nature of the scattering is associated with the absence of a preferred direction of the Abrikosov vortices, which is caused by the random orientation of the ab planes of the anisotropic superconductor granules.
We report on the magnetostriction of hexagonal HoMnO
3
and YMnO
3
single crystals in a wide range of applied magnetic fields (up to
H
= 14 T) at all possible combinations of the mutual orientations ...of magnetic field
H
and magnetostriction Δ
L/L
. The measured Δ
L/L
(
H, T
) data agree well with the magnetic phase diagram of the HoMnO
3
single crystal reported previously by other authors. It is shown that the nonmonotonic behavior of magnetostriction of the HoMnO
3
crystal is caused by the Ho
3+
ion; the magnetic moment of the Mn
3+
ion parallel to the hexagonal crystal axis. The anomalies established from the magnetostriction measurements of HoMnO
3
are consistent with the phase diagram of these compounds. For the isostructural YMnO
3
single crystal with a nonmagnetic rare-earth ion, the Δ
L/L
(
H, T
) dependences are described well by a conventional quadratic law in a wide temperature range (4–100 K). In addition, the magnetostriction effect is qualitatively estimated with regard to the effect of the crystal electric field on the holmium ion.
Composite materials fabricated by annealing of nonsuperconducting ceramics La
2
CuO
4
and La
1.56
Sr
0.44
CuO
4
at 910 °C during various time are investigated. Areas of superconducting La
1.85
Sr
...0.15
CuO
4
phase arises at boundaries of contacting nonsuperconducting granules. The volume fraction of the superconducting phase increases with increasing annealing time. A model describing the magnetic and transport properties of the samples at low magnetic fields is constructed. The magnetotransport characteristics of obtained samples at low magnetic fields (∼ 100 Oe) are defined by weak links network formed by superconducting areas. At high fields, behavior of the system is defined by a magnetization of the disconnected superconducting islands. The average size of the superconducting areas has been estimated from an extended critical state model.
In this report, we prepared for the first time the orthorhombic Dy
1−
x
Ho
x
MnO
3
single crystals with
x
= 0, 0.1, 0.2, 0.3, and 0.4 using the flux technique. The post-growth processing and ...chemical and structural characterization of the synthesized samples were performed. Also, we examined the samples obtained by their magnetic properties and the magnetic anisotropy in wide ranges of temperatures and magnetic fields.
The magnetostriction of HoMnO3 hexagonal single crystals was investigated for a wide range of applied magnetic fields with strengths up to H=14T for all possible combinations of magnetic field ...orientation H and magnetostriction ΔL/L. The anomalies found in the magnetostriction measurements of HoMnO3 correlate well with the phase diagram of these compounds. For the first time the measurements of magnetostriction of HoMnO3 single crystal were made in all five possible configurations.
The hysteretic behavior of magnetoresistance R(H) of the granular high-temperature superconductor (HTS) HoBa.sub.2Cu.sub.3O.sub.7 - delta has been investigated. The YBCO superconductors with a ...rare-earth element (Nd, Ho, Er, Sm, Yb, or Dy) with the magnetic moment in the yttrium site are characterized by a significant paramagnetic contribution to the total magnetization. The main goal of this study has been to establish the possible effect of this paramagnetic contribution on the magnetotransport properties, which are determined by tunneling of superconducting current carriers through the grain boundaries. An analysis of the results obtained basing on the concept of an effective field in the intergrain medium showed that the distribution of the magnetic induction lines from the paramagnetic moments is fundamentally different from that of the Meissner currents and Abrikosov vortices. The magnetic induction lines from the paramagnetic moments are not concentrated in the region of grain boundaries and therefore insignificantly affect the magnetotransport properties of a granular HTS. At the same time, the magnetic induction lines are strongly concentrated in the grain boundaries, which is caused by the Meissner currents and Abrikosov vortices, due to the features of their properties. Specifically, the magnetic flux compression determines the magnetotransport (in particular, the R(H) hysteresis) properties of granular HTSs, including 1-2-3 ones, with a rare-earth ion with the magnetic moment.
The paper deals with the examples of the use of microsegregation of chemical elements in powder particles of the Inconel 718 heat-resistant alloy for synthesizing on it's basis the “core-shell” type ...composite metal-ceramic particles in the inductively coupled plasma. A laboratory plasma treatment plant having a quartz plasmatron with a power of 40 kW and a frequency of 5.2 MHz was used. The spheroidization and degassing of the starting material were performed. It was established that, as the powder moved in the plasma flow, the explosive degassing of its particles, with the internal gas pores, took place first, and then the powder melted and spheroidized. It was shown that during the plasma treatment of the Inconel 718 powder in the presence of oxygen, microsegregation of the chemical elements contained in this alloy took place, with the formation of “core-shell” type composite metal-ceramic particles. The metal core consists predominantly of nickel, while the composition of the ceramic shell includes chromium and iron oxides, as well as spinels of the NiCr2O4 and NiFe2O4 types. By varying the oxygen concentration in the plasma, the shell thickness and the core diameter of the composite particle can be changed. The method makes it possible to synthesize metal-ceramic composite powders of the “core-shell” type for additive manufacturing.
Display omitted
•Explosive degassing and spheroidization occurs during powder plasma treatment.•Incorporating oxygen during Inconel plasma treatment forms ‘core-shell’ particles.•Oxygen concentration in plasma allows to control sizes of the core and shell.•Metal cores of the particles are based on nickel.•Ceramic shell is based on Fe and Cr oxides and spinels of the NiCr2O4 and NiFe2O4.
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