J. Maňka

Simplified fast method for magnetic characteristics measurement of the HTc superconducting materials

Abstract A simple measuring method and system for fast measurement of HT c superconductors characteristics are described. The measured sample is inserted into a low-frequency magnetic field in the center of two oppositely oriented coplanar coils with different diameters. The coils together with the sample are placed in the vessel with LN 2 which is outside the LHe cryostat. The currents in the coils are set up in such a way that before inserting the sample the compensated state (zero signal on the system output) is reached in the space of the pickup coil of the SQUID 2nd order gradiometer. After inserting the sample the compensation is disturbed and the arising signal is proportional to the equivalent dipole magnetic moment which characterizes the investigated superconducting material. The experimental measuring system reaching a sensitivity of order 10 -7 A m 2 at a frequency of the magnetizing field ⩽1 Hz is described. Measured magnetization hysteretic characteristics of the short-period melted HT c Bi superconductor are given.

Approaching the pT range with a 2DEG InGaAs/InP Hall sensor at 77 K

Abstract The noise of two-dimensional electron gas InGaAs/InP Hall sensors of various dimensions was studied. In the first part of the work we show that for large-scale sensors (>0.2 mm linear dimension) at 77 K and at 1 kHz, a sensitivity better then 1 nT can be achieved. The second part of present work deals with the noise measurements of 2 and 10 μm sensors dependent on bias current, frequency, applied magnetic field and temperature. It was found that the low-frequency noise of the 10 μm sensor rapidly increased for applied magnetic field, but the noise of the 2 μm sensor is a complicated function of temperature and magnetic field: for low temperatures and fields 1–3 T is the low-frequency noise of the sensor suppressed.

Synthesis and Transport Properties of Nanostructured VO2 by Mechanochemical Processing

Synthesis and Transport Properties of Nanostructured VO2 by Mechanochemical Processing The high-energy milling of the V2O5-Na2SO3 mixture in the range of 5 - 100 min leads to a synthesis of monoclinic VO2. The starting and minimum (at 220 °C) values of electric resistance R of the 100 min milled and pressed VO2-Na2SO4 mixture were 13.9 MΩ and 91.5 kΩ, respectively. The subsequent washing of the as-milled powder partially leads to the development of VO2 nanostructures with tube-like, sheet-like and rod-like morphology, besides VO2 (B) belt-like morphology, depending on the milling times.

SWITCHING MAGNETIZATION MAGNETIC FORCE MICROSCOPY --- AN ALTERNATIVE TO CONVENTIONAL LIFT-MODE MFM

Switching Magnetization Magnetic Force Microscopy — An Alternative to Conventional Lift-Mode MFM In the paper we present an overview of the latest progress in the conventional lift-mode magnetic force microscopy (MFM) technique, achieved by advanced MFM tips and by lowering the lift height. Although smaller lift height offers improved spatial resolution, we show that lowered tip-sample distance mixes magnetic, atomic and electric forces. We describe an alternative to the lift-mode procedure - Switching Magnetization Magnetic Force Microscopy [SM-MFM], which is based on two-pass scanning in tapping mode AFM with reversed tip magnetization between the scans. We propose design and calculate the magnetic properties of such SM-MFM tips. For best performance the tips must exhibit low magnetic moment, low switching field, and single-domain state at remanence. The switching field of such tips is calculated for Permalloy hexagons.

Gadolinium Scandate: Next Candidate for Alternative Gate Dielectric in CMOS Technology?

Gadolinium Scandate: Next Candidate for Alternative Gate Dielectric in CMOS Technology? The films of GdScO3 were prepared by liquid injection metal-organic chemical vapor deposition, MOCVD at 600 °C on (100) Si substrate. The as-deposited films were amorphous with a smooth surface and sharp GdScO3/Si interface. X-ray diffraction showed that the amorphous phase is well preserved upon rapid thermal annealing up to 1000 °C. It is shown, that exact stoichiometry of GdScO3 is not necessary to achieve dielectric constant above 20.

The effect of rare earth oxide substitution on the magnetic properties of Tl-based superconductors

Abstract The effects of the heterovalent substitution of the rare earth ions La3+, Sm3+, Pr3+, Dy3+ and of Y3+ into the Ca2+ separating layers on the magnetic properties of (Tl,Pb)-1223 and (Tl,Pb)-1212 superconductors are reported. Nominal compositions of (Tl0.6Pb0.5)(Sr0.8Ba0.2)2(Ca1−xMx)2Cu3O8+δ, where M=La, Sm, Pr, Dy, Y and x=0.0, 0.05, 0.1, 0.15 and 0.2 were investigated. Increasing contents of the rare earth elements enlarged the superconducting Tl-1212 phase in the samples. This led to a decrease of the Tc values. AC and virgin volume magnetization characteristics of all fabricated samples were measured at 77.3 K in magnetic fields ranging from 10−1 to 105 Am−1. A decrease in the content of the Tl-1223 phase affected the magnetization mainly in the range of stronger fields around 105 Am−1. For the lower substitution levels (x=0.05, 0.1) an improvement of the intergrain links was found.

Effects of Slight Non-Stoichiometry in Sm-Ba-Cu-O Systems on Superconducting Characteristics

Effects of Slight Non-Stoichiometry in Sm-Ba-Cu-O Systems on Superconducting Characteristics We studied the effects of slight Sm-Ba non-stoichiometry in Sm-Ba-Cu-O superconducting compounds on their transition, structural, and magnetic properties. Two series of single-phase samples of Sm1+xBa2-xCu3O7+Δ and Sm1+xBa2-xCu3O7+Δ with composition deviation from stoichiometry x from 0 to 0.1 were synthesized by the solid-state reaction method from Sm2O3, BaCO3 and CuO precursors and sintered at the temperature of ~ 1060 °C in flowing oxygen. All samples showed the values of Tc > 90 K and the volume density, p, 6.45 g cm-3 < p ≤ 6.73 g cm-3. The effect of the composite deviation of x on Tc, ΔTc, and volume magnetization M was studied. For Sm1+xBa2-xCu3O7+Δ compounds, optimal values of x were determined to maximize the width of the magnetization hysteresis at higher values of the applied magnetic field, corresponding mainly to the grain contribution. We also prepared the Sm1+xBa2-xCu3O7+Δ samples with x from 0 to 0.1 using the same processing conditions as in the case of A and B series. For the Sm1+xBa2-xCu3O7+Δ samples, values of x = 0.02 - 0.03 optimize Tc, ΔTc, Hp1 as well as M.

Automatic Apparatus for Simultaneous Measurement of Resistance and Inductance Temperature Transition Dependences of Superconductors

Automatic Apparatus for Simultaneous Measurement of Resistance and Inductance Temperature Transition Dependences of Superconductors An automatic measurement complex for the study of transition properties of HTc superconductors using the transport method of the measurement of the resistance temperature dependence and the contactless mutual inductance method of the measurement of temperature dependence of the induced voltage based on the Meissner-Ochsenfeld effect have been developed. In addition, temperature dependences of harmonic components of the induced voltage may be measured simultaneously using the Brüel & Kjaer signal analyzer. Results of transport and induced voltage measurements are compared using YBCO superconductors with distinct grain and intergrain properties prepared by different technological procedures. The question of the mutual compatibility of such methods is discussed.

Influence of the Tl- and Hg-content on magnetic and transport properties of the Pb, Sr-doped Tl-1223 and Hg-1223 superconductors

Abstract The effects of the thallium and mercury content x on the as-sintered and post annealed samples of M x Pb 0.4 Sr 1.6 Ba 0.4 Ca 2 Cu 3 O 8+ δ {M: Tl (0.32≤ x ≤0.74) or Hg (0.18≤ x ≤0.68)} have been studied by magnetization and transport measurements. For Tl-1223 we have found the optimum Tl doping level to be x =0.53 regarding the grain properties, the content of superconducting phase, the first penetration field H pl wl , the transport ( J c tr ), magnetic intergrain ( J c M ) and intragrain ( J c g ) critical current densities. The critical temperature T c of the as-sintered Tl-1223 sample decreased with increasing Tl content. Post-annealing in oxygen improved the T c for Tl contents of x ≥0.53 and had generally positive effects on the critical current densities. The intergrain properties of the Hg-1223 samples were much worse than those of the Tl-based superconductors.

Experimental study of the intergranular weak link structures YBa2Cu3O7−x with the help of magnetization measurements

AC and DC virgin magnetizations of sintered YBa2Cu3O7−x samples have been measured in dependence of the sintering temperature. The samples were prepared by solid state reaction of stoichiometric decarbonated mixture of Y2O3, BaCO3 and CuO components. Magnetization curves were measured at 77K in the range of magnetic field (10−1−2×104Am−1). The temperature of sintering was being changed in the range 910°C up to 950°C. In the range of weak magnetization fields the magnetization curves are affected by properties of the intergranular medium — the intergranular weak links. The parameters H1w1, H2w1 and H1g characterising the flux penetration into intergrain and intragrain medium were estimated from the magnetization measurements.