Temperature, field and frequency dependence of intergranular AC loss in high-temperature superconductors

Savvides, N.; Katsaros, A.; Andrikidis, C.; Müller, K.‐H.

doi:10.1016/0921-4534(92)90009-2

Cited by 25 publications

(13 citation statements)

References 21 publications

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“…Bonsignore et. al noticed a strong field dependence even at low fields (~0.007 Oe); it is worth to remark that in high T c cuprates T p nearly saturates for H ac <0.1 Oe [34,35]. It is also noted that values of maximum M"(T p ) is increasing monotonically with increasing field.…”

Section: Resultsmentioning

confidence: 91%

Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50 K superconductor

et al. 2010

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We report an easy single step synthesis route of title compound Although by now nearly two years are over after the discovery of superconductivity in C. Finally the sample was allowed to cool down to room temperature. All the heating schedules were given in one single step. The resultant compound was hard enough for transport measurements and was black in color. Typically, 1 gram of raw pellet was sealed in 2.5 cm diameter and 10 cm length high quality "thick walled" quartz tube. The X-ray diffraction pattern of the compound was taken on a Rigaku diffractometer using CuK α radiation and the Rietveld analysis was carried out to know the lattice parameters and impurities etc., if present at all. Magneto-resistivity measurement R(T)H up to 14 T Field and DC magnetic susceptibility in both zero-field-cooled (zfc) and field-cooled (fc) situations along with the isothermal magnetization (MH) measurements were carried out on a physical property measurement system (PPMS) from Quantum Design (QD). The AC susceptibility at different frequencies (33 to 9999 Hz) & different amplitudes (1 to 15 Oe) of AC drive field with 4 temperatures down to 5 K, the specific heat with temperature down to 2.2 K and thermo-electric power (TEP) were also measured on the same physical property measurement system (PPMS). Figure The upper critical field is determined using different criterion of H c2 =H at which =90% N or 50% N or 10% N , where  N is the normal resistivity or resistance at about 51 K. RESULTS AND DISCUSSIONThe H c2 variation with temperature is shown in Figure 2(c). To determine H c2 (0) value, we applied Ginzburg Landau (GL) theory. The GL equation is:Where, t=T/T c is the reduced temperature [18]. DC magnetic susceptibility versus temperature plot in both zero-field-cooled (zfc) and field-cooled (fc) situations is given in Figure 3. The applied magnetic field is 50 Oe.Superconductivity sets in below 49 K, as evidenced from clear diamagnetic signal at this temperature. Although the transition seems slightly broad the same is still sharper than previous reports on polycrystalline NdFeAsO/F [14,15]. Both zfc and fc are nearly saturated below 30 K.As far as the determination of superconducting volume fraction is concerned the same cannot be ascertained without ambiguity primarily due to positive paramagnetic contribution to magnetic susceptibility from Nd/Fe moments and secondly the pinning defects and impurities hamper the real outcome. Still one can say with confidence that the studied compound is a bulk superconductor with shielding fraction above 25% and superconducting volume fraction of > 8%. 7Measurement of the AC susceptibility can be conveniently used to investigate both intergrain and intragrain vortex dynamics in superconductors [31][32][33]. Figure sample is a granular superconductor like other reported oxy-pnictides.The temperature variation of the AC susceptibility measured at different AC field amplitudes 1, 2, 4, 6, 8, 10, 12, 13 & 15 Oe is shown in Figure 5. The diamagnetic onset temperature is ~ 47.7 K...

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Section: Resultsmentioning

confidence: 91%

Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50 K superconductor

et al. 2010

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“…4. One can note a strong field dependence even at low H ac values; it is worth to remark that in high-T c cuprates T p nearly saturates for H ac 0.1 Oe [19,24].…”

Section: Resultsmentioning

confidence: 99%

Intergrain Effects in the AC Susceptibility of Polycrystalline LaFeAsO0.94F0.06

et al. 2010

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The AC susceptibility, χ, at zero DC magnetic field of a polycrystalline sample of LaFeAsO 0.94 F 0.06 (T c ≈ 24 K) has been investigated as a function of the temperature, the amplitude of the AC magnetic field (in the range H ac = 0.003 Oe ÷ 4 Oe) and the frequency (in the range f = 10 kHz ÷ 100 kHz). The χ(T ) curve exhibits the typical two-step transition arising from the combined response of superconducting grains and intergranular weak-coupled medium. The intergranular part of χ strongly depends on both the amplitude and the frequency of the AC driving field, from few Kelvin below T c down to T = 4.2 K. Our results show that, in the investigated sample, the intergrain critical current is not determined by pinning of Josephson vortices but by Josephson critical current across neighboring grains.

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“…The characteristic peak position T P moves toward right and its height increases monotonically with increasing frequency. The frequency variation from 208 to 999 Hz leads to a T P shift of about 12 K. The frequency dependence of χ is much higher than that reported for YBCO and high‐ T C cuprates . The onset temperature of χ′ was not modified by frequency; however, the double step nature of transition in χ′ was suppressed above 533 Hz.…”

Section: Resultsmentioning

confidence: 77%

SmFeAsO Superconductor with Preferred Crystallographic Orientation and Enhanced Critical Current Density

et al. 2014

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The effect of combined substitution of Sm 3+ and O 2− with Ca 2+ and F − , respectively, on the structural and superconducting properties of SmFeAsO system is investigated. It is observed that the binary doping using CaF 2 causes considerable structural as well as microstructural changes wherein the preferred orientation of (00 l) planes and enhancement of grain size are quite interesting. Moreover, a maximum T C of 53.8 K and a transport J C of 880 A/cm 2 (12 K) are achieved in the codoped samples. The achievement of preferred orientation, enhanced T C , and the subsequent increase in J C of the modified SmFe-AsO system are particularly significant for high current conductor development.

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Temperature, field and frequency dependence of intergranular AC loss in high-temperature superconductors

Cited by 25 publications

References 21 publications

Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50 K superconductor

Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50 K superconductor

Intergrain Effects in the AC Susceptibility of Polycrystalline LaFeAsO0.94F0.06

SmFeAsO Superconductor with Preferred Crystallographic Orientation and Enhanced Critical Current Density

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