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SHS technique and conventional melting and casting technology were combined and used for the preparation of Al-Ti-C grain refiner alloy. Experimental results show that when SHS reaction occurs to the Al, Ti and C powder reactant in Al melt and the composition proportion factor, n , is between 4 and 10, the effect of composition on the initial temperature of SHS reaction is small and its initial temperature ranges from 810 to 815°C. However, the highest temperature of the melt increases with increasing n values and increases gradually from 845 to 1370°C. In the meantime, when the composition proportion factor for Al, Ti and C powder reactant, n, is greater than 5.95, its adiabatic temperature Td>1800K which conforms to the empirical criterion proposed by Merzhanov et al. The SHS reaction of reactant can accomplish by self-maintenance.

A high-temperature superconducting (HTS) filter subsystem consisting of a 10-pole HTS filter with group delay self-equalization, a cryogenic low noise amplifier (LNA), and a cooling device is presented in this paper. The HTS filter has a 0.51% fractional bandwidth at 1955 MHz, simulated in Sonnet, and is fabricated using double-sided Tl2Ba2CaCu2O8 films on 0.5 mm thick LaAlO3 substrate. Measured responses show that the minimum insertion loss of the filter is 0.16 dB, and the out-of-band rejection is better than 75 dB. The slope is 27 dB MHz−1 at the low band edge and 22 dB MHz−1 at the upper band edge. The HTS filter subsystem has a gain of 19.3 dB and a noise figure (NF) of 0.8 dB. Furthermore, the phase distortion of HTS filters is considered, and an efficient design approach for self-equalized HTS filters is proposed.

The empirical tuning of high temperature superconducting (HTS) filters is usually time-consuming and expensive. A computer-aided tuning method is presented in this paper. By means of optimization, the method diagnoses detuning of individual resonators quantitatively in the tuning process, and then by using neural network models the method is able to give the operator a decision on how much the corresponding tuning screws should be tuned. So, compared with the empirical tuning method, this method can be used to tune the HTS filters accurately with less time and cost.

We fabricated (Tl0.95Bi0.2)(Sr0.8Ba0.2)2Ca2Cu3Ox (Tl, Bi-1223) superconducting thin films on a LaAlO3(001) substrate by a three-step process including magnetron sputtering and two post-annealing processes. In the post-annealing process we found that the (Tl0.95Bi0.2)(Sr0.8Ba0.2)2Ca1Cu2Ox (Tl, Bi-1212) phase formation played a very important role in obtaining the Tl, Bi-1223 superconducting phase. So, the precursors were annealed at lower temperature to form the Tl, Bi-1212 phase entirely, and then almost pure Tl, Bi-1223 phase superconducting thin films could be obtained by annealing the Tl, Bi-1212 film at higher temperature. The superconducting critical temperature Tc of the Tl, Bi-1223 film annealed in oxygen and in argon was 111 K and 107 K, respectively. The critical current density Jc (77 K, 0 T) of the Tl, Bi-1223 film annealed in oxygen was as high as 3.7 MA cm−2.

A 10-pole self-equalized high-temperature superconducting (HTS) filter is presented in this paper. The filter has a fractional bandwidth of 0.51% at 1955 MHz, simulated in Sonnet, and is fabricated using double-sided Tl 2 Ba 2 CaCu 2 O 8 film on 0.5 mm thick LaAlO 3 substrates. The filter consists of 10 novel quasi-lumped resonators and an additional microstrip which is used to realize the real-axis transmission zeros (TZs). The simulated group delay ripple over the central 55% of the filter’s passband is 5.6 ns, and a close result of phase response is achieved in laboratory test. The measured insertion loss of the filter is less than 0.2 dB, the out-of-band rejection is better than 75 dB and the slope is better than 22 dB MHz −1 at band edge.

Nonlinear inductance of intrinsic Josephson junction arrays in Tl-2212 thin films has been investigated. Misaligned Tl-2212 thin films were fabricated on 20deg vicinal substrates and then patterned into long bridges by standard photolithography and wet chemical etching. Each bridge forms a large array of intrinsic Josephson junctions. We have measured the Josephson inductance of the bridges in the zero-DC-voltage state at 77 K and show that its dependence on the critical current is in a good agreement with theory. Also, we have numerically studied the nonlinearity of the Josephson inductance and present dependence of the distortion factor on the bias and AC signal currents. Based on the obtained results, we have designed a 10-pole narrow-band lumped-element filter with the tunable center frequency in the range from 1900 MHz to 1960 MHz. Simulations show that the filter has good selectivity.

An open-ended dielectric resonator method and experimental apparatus for measuring microwave surface resistance of the high Tc superconducting thin films are reported. Making use of two sapphire rods the quality factor related to the losses of the resonator except its superconducting part can be evaluated. The Rs value of an individual superconducting thin film can be determined without any assistance of other superconducting films or calibrators. This measurement provides a convenient and absolute approach for Rs-measurement of high Tc superconducting thin films. Also the error in the Rs-measurement with the method was discussed.

Long intrinsic Josephson junction arrays (3.4 mm) were successfully fabricated in misaligned Tl 2 Ba 2 CaCu 2 O 8 thin films grown on 20° vicinal substrates. The array consists of about 7.7 × 10 5 intrinsic Josephson junctions. The I – V characteristic was recorded and compared with that of a 6 μm long array. The inductance of the ultra-long junction array in zero-voltage state was observed and measured directly. The measured value is basically consistent with the theoretically calculated result, confirming that the inductance is mainly due to the Josephson effect. The inductance from the Josephson effect is one order of magnitude larger than that from other effects, suggesting a new idea of the use of intrinsic Josephson junction arrays as new type of inductors with small size and large inductance.

The preparation and properties of Tl-2212 (Tl2Ba2CaCu2O8) thin films on biaxially textured Ni substrates, buffered with CeO2/YSZ/CeO2 trilayers, have been studied. Tl-2212 thin films were grown using a two-step fabrication process that involved magnetron sputtering and low temperature post-annealing. XRD θ–2θ scans, rocking curves and -scans proved that the Tl-2212 thin films were epitaxially grown on the buffered RABiTS. The critical temperature Tc and critical current Jc (77 K, 0 T) were 103 K and 2.6 MA cm−2, respectively.

A planar structure of group-delay equalizer, which is built on high temperature superconducting (HTS) films, is proposed in this article. The HTS equalizer consists of one microstrip 3-dB hybrid and two identical 1-port coupled-resonator filters. Compared with the traditional equalizers composed of cavity or coaxial resonators, the HTS equalizer has the advantages of smaller insertion loss and smaller size. As an example, a 3-pole HTS equalizer is designed to equalize a 6-pole HTS filter and good performance is achieved. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2163–2165, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22681

Using first-principles calculation based on density functional theory, we study the magnetic anisotropy of Gd-adsorbed graphene and its dependence on carrier accumulation. We show that carrier accumulation not only impacts the magnitude of magnetic anisotropy but also switches its sign. Hole accumulation enhances the perpendicular anisotropy up to ∼16 meV per Gd atom, while electron accumulation switches the anisotropy from perpendicular to in-plane direction. Moreover, we find that the first order perturbation of spin-orbit coupling interaction induces a pseudo-gap at Γ for the perpendicular magnetization, which leads to the the anomalous magnetic anisotropy for the neutral composite. Our findings pave the way for magneto-electric materials based on rare-earth-decorated graphene for voltage-controlled spintronics.

Based on density functional theory with the generalized gradient approximation, a computational study is carried out to reveal the magnetism of the hexagonal boron nitride monolayers (h-BN) doped by 3d transitional metal atoms at boron-site. The magnetic moments and magnetic anisotropy energies (MAEs) of the most stable structures are given. Among the systems investigated, the MAE of Fe doped h-BN is 1.19 meV with an easy axis in the h-BN plane, while that of Mn is 0.63 meV with an easy axis perpendicular to the plane. For Sc and Co, the doped systems are nonmagnetic. For Ti, V, Cr, Ni, Cu, and Zn, the MAEs are relatively small. Theoretical analyses by perturbation theory and molecular orbital clarify that the MAE of Fe originates from the second order spin orbit coupling, whereas the MAE of Mn is contributed by the unquenched orbital momentum.

The dynamics of capacitively coupled intrinsic Josephson junction arrays with a McCumber parameter βc