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Within the effective field theory, we investigate critical behaviors of transverse crystal field and bimodal magnetic field mixed spin-1/2 and spin-1 Ising model with bond dilution or percolation threshold on a simple cubic lattice. A-type double tricritical points and zigzag reentrant phenomenon can be found at pure bond and large bimodal magnetic field status. The ordered phase is impaired sharply due to bond dilution. The positive transverse crystal field can induce ordered phase at ordinary bond percolation threshold. The bimodal magnetic field can suppress the induced ordered phase and form a series of closed ordered regions. An extraordinary bond percolation threshold is determined, at which the induced ordered phase vanishes completely. The different effects of bimodal magnetic field and bond percolation threshold on induced ordered phase are discussed.

Un-substituted TlBa2Ca2Cu3O x (Tl-1223)-superconducting thin films have been fabricated on a LaAlO3 (001) substrate in oxygen by using a two-step method, which includes direct current (DC) magnetron sputtering and post-annealing process. Thallium (Tl) content in amorphous precursor films is found to be important to the crystallization of Tl-superconducting phase. Using the nominal composition of Tl1+δ Ba2Ca2Cu3 O 8 (δ = 0.1∼0.2) precursor films, the formation is promoted to Tl-1223 and Tl-2223 phase rather than Tl-1212 and Tl-1223 phase with accompanying Tl-rich source pellets. When the annealing process continues, Tl-2223 phase will be converted to Tl-1223 phase at a suitable annealing time and temperature. From the X-ray diffraction pattern, only Tl-1223 (00l) peaks are observed, which shows that the purity of Tl-1223 film is improved significantly by this method. The critical temperature T c of Tl-1223 film is characterized at 110 K, and the critical current density J c (77 K, T = 0) is up to 1.5 MA/cm2.

Within the effective field theory (EFT), the compensation behaviors of mixed spin-1/2 and spin-1 Ising model with transverse crystal field in an external magnetic field are studied on a simple cubic lattice. The model exhibits two types of temperature and magnetic compensation point ( T k and h k ) in M − T and M − h space, respectively. At zero or nonzero magnetic field, the single or double T k is induced by positive transverse crystal field ( + D x / J ), but not or only the single T k in negative crystal field ( − D x / J ). The single h k is discovered and adjusted by ± D x / J . A complex oscillation of magnetization curves at low magnetic field and large ± D x / J can be observed. The ranges of ± D x / J which can induce the h k take on an opposite tendency and the oscillation phenomena become weak when the temperature is up. In particular, the influence of transverse crystal field on the temperature and magnetic compensation point is primarily proposed in this work.

We have investigated the millimeter wave irradiation characteristics of misaligned Tl2Ba2CaCu2O8 thin-film intrinsic Josephson junction arrays at a liquid nitrogen temperature in an antenna system by both simulation and experiments. The dielectric substrate was regarded as a dielectric resonance antenna to improve high-frequency electromagnetic coupling between the intrinsic Josephson junction array and a horn antenna. A useful model for simulating the microwave system was devised to demonstrate and analyze the optimization of the irradiation in the antenna system. The electric field distribution in the antenna system was computed and displayed. Also, the near-field and far-field frequency characteristics of the receiving antenna and transmitting antenna were calculated and analyzed to study the mechanism of the irradiation. In the experiment, by detecting the suppressed critical current of the IJJA, an optimum transmission frequency range was measured and the frequency characteristic was studied in the transmitting and receiving antenna system. The critical current of the IJJA was suppressed to 37 % and the optimum coupling effect was achieved at 74.8 GHz. And the electromagnetic simulation matched up well with the experimental result. Potential reasons of the acceptable nuances between the simulation and experiment results were also taken into account. The influence the size of the microbridge had on the frequency characteristic of the dielectric antenna were elaborately discussed.

Magnetic properties of the bond and crystal field dilution spin-3/2 Blume–Capel model in an external magnetic field ( h ) on simple cubic lattice are studied by using the effective field theory. In the m − T plane, the degeneracy of the magnetization ( m ) is affected by the concentration of bond or crystal field dilution at low temperature ( T ) . The magnetization curves can appear to fluctuate in certain regions of negative crystal field. In the m − h plane, the initial magnetization curve has an irregular behavior due to the introduction of bond dilution. The crystal field dilution has the influence on the process of magnetic domain displacement. In the χ − h plane, there exists one susceptibility ( χ ) shoulder and one step for different negative crystal field. The susceptibility curve takes on the feature of multi-peaks distribution under bond and crystal field dilution conditions.

The static globularization behavior and mechanism of transformed structure during heat-treatment of hot worked TA15 alloy were investigated. It is found that boundary splitting and microstructure coarsening are two competing mechanisms for static globularization. Boundary splitting is significant in the initial stage of annealing while coarsening occurs throughout the annealing process. Static globularization kinetics increases with annealing temperature and prestrain, but is independent on strain rate. The rate of static globularization kinetics decreases with annealing time. The asymptotic equation can be used to model the static globularization kinetics.

Control of microstructure morphology in isothermal local loading of titanium alloys is important to obtaining high performance components. To this end, the effect of thermo-mechanical processing on the microstructure development of TA15 alloy during isothermal local loading was experimentally investigated. It is found that bi-modal or equiaxed microstructure can be achieved when the heating temperature of the last loading step is not lower than that of the previous loading step. The volume fraction of primary alpha phase and the morphology of transformed beta matrix are determined by heating temperature and cooling rate in the last loading step, respectively. Tri-modal structure can be achieved by near-beta forging followed by conventional forging in the last loading pass. The volume fraction of each constituent phase in tri-modal structure is determined by the heating temperatures of the last two loading steps. The emergence of secondary alpha platelets in beta phase is promoted by increasing the heating temperature or cooling rate of the last loading step. Globularization of alpha lamellae can be avoided by thickening the alpha laths or decreasing the deformation degree in the last loading pass.

In this paper, an effective method for improving emissions from Josephson junction arrays was proposed. We took the substrate as a dielectric resonance antenna to improve the coupling of intrinsic junctions to electromagnetic waves. Electromagnetic simulations were performed in parallel with experiment investigations. Sharp radiation peaks at 76.9 GHz were detected from intrinsic Josephson junction arrays in misaligned Tl2Ba2CaCu2O8+δ thin films at 78 K. Experimental results proved the effectiveness of this method, which offered a competitive choice for coherent emission from intrinsic Josephson junction arrays.

Phase transition properties of a spin-1 Blume–Emery–Griffiths model (BEGM) with random transverse crystal field is studied by the effective field theory for a simple cubic lattice. In T − D x space, we obtain the phase diagrams with the ratio α between the biquadratic interaction and the exchange interaction as well as a tunable parameter l of the transverse crystal field. The tricritical point (TCP) appears at α 0 , which undergoes a crossover from positive to negative direction of the transverse crystal field when l 0 . The TCP cannot be observed for α > 0 . The maximum critical temperature increases with the increase of α . The position of the peak value tends to the drift of negative or positive direction for a different magnitude or an imperfect ( ± ) transverse crystal field distribution. In T − α space, the range of ordered phase is magnified when the ratio is changed from α 0 to α > 0 . The random transverse crystal field obviously affects the TCP.

We report the in-plane temperature dependent ac impedance spectrum of Tl 2 Ba 2 CaCu 2 O 8+ δ (Tl-2212) single crystal film with thickness 3000 A and T c = 96 K. In process of the superconducting condensation, the impedance spectrum z ( ω , T 0 ) changed considerably and was very similar with the evolution of the spectrum under various dc bias voltages in the shallow superconducting state. The spectrum weight transfers from high frequency regions to lower ones and eventually diverges towards the dc limit. From the analysis, it seems that the superconducting ‘islands’ form first and then grow larger, till the formation of a ‘continent’. The impedance spectrum z ( ω , B I ) at various dc bias B I have also been studied.

The millimeter-wave responses of the intrinsic Josephson junctions (IJJs) in misaligned Tl 2 Ba 2 CaCu 2 O 8 thin film have been experimentally studied. In the low voltage part on the current–voltage ( I–V ) characteristics, sloping steps are induced under different frequencies. By presenting the dV/dI–I curves, it shows that corresponding to the sloping steps on the I–V characteristics, resistive bumps appear. The dV/dI–I and dV/dI–V plots from 72 GHz to 80 GHz and at different power show the variation of the step voltage.

Within the effective field theory (EFT), this work studies the compensation behaviors and magnetization processes of different transverse fields mixed spin-1/2 and spin-1 Blume–Capel models in a magnetic field. We obtain double temperature compensation points and a single magnetic compensation point on a simple cubic lattice. The effects of the different sublattice transverse fields and a crystal field on the compensation point and magnetization are discussed in M – T and M – h space. The magnetic compensation point offers a new route in the field of magneto-optic recording. On the other hand, the magnetization processes undergo interesting and complex varieties under the different transverse field conditions. In particular, there is a super-saturation magnetization process for a spin-1/2 sublattice transverse field.

Within the effective field theory (EFT), we investigate critical behaviors and magnetic multi-compensation points of bond dilution mixed Blume–Capel model in bimodal magnetic field, for a simple cubic lattice. The tricritical point (TCP) always exists for all h / J values in T − D space, while the TCP appears in smaller or larger range of negative D / J values for T − h space. The bond dilution can depress the TCP. The influence of crystal field and bimodal magnetic field on the induced ordering phase at bond percolation threshold is revealed. The system takes on one or two novel magnetic compensation points in M − h space. The bond dilution has the effect of changing one or two magnetic compensation points. The magnetic multi-compensation points offer a new route in the field of magneto-optic recording.

The phase diagrams and compensation behaviors of mixed spin-1/2 and spin-1 Blume–Capel model in a trimodal magnetic field are investigated in the framework of the effective field theory on simple cubic lattice. The change of negative crystal field and trimodal concentration can affect the TCP, the second-order phase and the magnetic field degeneration at ground state in T – H space. In T – D space, the trajectory of the TCP takes on the acre curve and there exist the two TCPs under certain condition. In addition to giving one or two compensation temperature points in M – T space, the mixed spin Blume–Capel model also provides one or two novel compensation magnetic field points in M – H space. Some results are not revealed in previous works.

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.

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.

Within the effective field theory (EFT), the critical properties of the biaxial Ising model with both longitudinal crystal field and transverse dilution crystal field are investigated for a simple cubic lattice. The tricritical point (TCP) and its trajectory are discussed in T – D x and T – D z space. A new phenomenon of two TCPs is found in T – D x space. There exists a second-order line between two first-order lines, separated by two TCPs. The change of dilution concentration leads to a complex relation of the trajectory of the TCP. The degenerate patterns at the ground state appear by changing the longitudinal crystal field. The range of the ordered phase for transition lines labelled as a positive or (negative) value of D x / J becomes larger or (smaller) with the decrease of t x in T – D z space. Some results have not been revealed in previous works.

The critical behavior of the spin-1 bond and crystal field dilution Blume–Emery–Griffiths model have been investigated on simple-cubic lattice within the framework of the effective field theory. In particular, both bond dilution and random crystal field are considered at the same time. The interplay between bond and crystal field dilution constructs rich and interesting phase diagrams. Significant distinctions are exhibited. When positive ratio α changes in a certain range, there exist double tricritical points in phase-transition lines in T – D plane. Moreover, this first-order phase transition is enlarged with increasing of ratio α at a fixed crystal field dilution concentration, while this first-order phase transition will shrink when bond dilution concentration is fixed. In addition, we observe that there exist two bond percolation thresholds for negative crystal field and α>0 in T – P plane.

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 magnetic properties of the spin-1 bond and crystal field dilution Blume–Emery–Griffiths (BEG) model in the presence of magnetic field are investigated on a simple cubic lattice by using effective field theory (EFT). In the M – H plane, the common action of bond and crystal field dilution leads to the exhibition of an irregular initial magnetization curve and slows down the magnetization process. The peak of the susceptibility curve has an explicit decline and shows a distinct shift toward the direction of increase of magnetic field. On the other hand, in the M – T plane, the magnetization curves show a discontinuity and a vertical leap in the small range of magnetic field when the negative crystal field is larger and the ratio of biquadratic and exchange interaction is positive ( α > 0 ) . These results have not been revealed in previous works.

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.

High quality Tl 2 Ba 2 CaCu 2 O 8 (Tl-2212) superconducting thin films are prepared on both sides of 2 in. LaAlO 3 (0 0 1) substrates by off-axis magnetron sputtering and post-annealing process. XRD measurements show that these films possess pure Tl-2212 phase with C -axis perpendicular to the substrate surface. The thickness unhomogeneity of the whole film on the 2 in. wafer is less than 5%. The superconducting transition temperatures T c s of the films are around 105 K. At zero applied magnetic field, the critical current densities J c s of the films on both sides of the wafer were measured to be above 2 × 10 6 A/cm 2 at 77 K. The microwave surface resistance R s of film was as low as 350 μΩ at 10 GHz and 77 K. In order to test the suitability of Tl-2212 thin films for passive microwave devices, 3-pole bandpass filters have been fabricated from double-sided Tl-2212 films on LaAlO 3 substrates.

Very thin Tl 2 Ba 2 CaCu 2 O x (Tl-2212) superconducting films with thickness 3 (0 0 1) substrates using dc magnetron sputtering and post-annealing process in pure argon. For a 100 nm thick film, T c and J c (77 K, 0 T) show the values of 105.3 K and 2.33 × 10 6 A/cm 2 , respectively. A 30 nm thick film with T c >100 K shows smooth surface morphology and high quality epitaxy. A 20 nm thick film revealed full transition to superconductivity at temperature of 98.7 K. The superconductivity and surface morphology of the very thin film deteriorated rapidly as the film thickness below 20 nm. A 6 nm thick Tl-2212 film was not found to be superconducting at temperature down to 15 K. In our experiments the critical film thickness leading to degradation of the superconducting properties was 20 nm.

The bond dilution spin-1 transverse ferromagnetic Ising model with random crystal field is investigated in the framework of effective field theory (EFT). The general expressions of magnetization are derived for lattice with any coordination number z. In particular, we calculate the phase diagrams of a square lattice. The second-order phase transition lines and the tricritical points are presented in different conditions for the square lattice. Special emphasis is placed on the influence of bond dilution, random crystal field and the transverse field on the phase diagrams. We discover some unusual phenomena. New results obtained in this paper are discussed in detail.

The bond dilution Blume–Capel model with random crystal field is considered in the framework of the effective field theory. The expressions of magnetizations for honeycomb and square lattices are derived. Special emphasis is placed on thermodynamic properties of the two lattices and the differences between them are compared. Some new phenomena are obtained in a certain range of crystal field, concentration of random crystal field and concentration of bond dilution. We discuss in detail the influence of the two different concentrations on thermodynamic properties. Some phenomena had not been discovered in the previous literature. A detailed description of the phase transition is presented.

Polymethyl methacrylate (PMMA) was investigated as a possible protective layer for HgBa2CaCu2Ox+δ superconducting thin films. Microwave surface resistance (Rs) and DC transport properties were measured on both virgin and PMMA-coated samples before and after they were exposed to certain environments including thermal cycling at high and low vacuums, air and water. At high vacuum near 0.5 mTorr, no degradation was observed on samples after undergoing 20 thermal cycles in the temperature range of 90–290 K. In the case of low vacuum ∼200 mTorr, only the coated samples showed stability after six thermal cycles. When exposed to air, the coated sample did not show any sign of degradation, whereas bare sample severely degraded during the same testing period. However, a long-term direct immersion in water could weaken the adhesion between PMMA and the film surface letting water penetrate. Hence, this polymer may be used as a protective layer for Hg-based superconductors against atmosphere-assisted degradation but not against direct water exposure.

A bond-diluted transverse ferromagnetic spin- 1 2 and spin-l system with crystal field is considered in the framework of the Ising model. The effective field theory and decoupling approximation are applied to derive the expressions of magnetizations for honeycomb lattice. New compensation behaviors and various magnetization curves are obtained in a certain range of bond concentration, transverse field and crystal field values. Some phenomena are not predicted by the Neel theory of ferrimagnetism. The influence of the various parameters on compensation behaviors is discussed in detail.

Enhanced superconducting properties in TlBa2CaCu2Ox (Tl-1212) thin films have been achieved by extra low-temperature annealing in pure argon. The oxygen content could be reduced from the more oxygen-rich film by the latter process. As the oxygen content approached an optimal value, the superconductivity of the Tl-1212 films could be significantly improved. The optimized critical temperature Tc of Tl-1212 thin films was up to 100 K and the critical current density Jc could be enhanced to 1.85×106 A cm-2 at 77 K. Slight changes occurred in the crystal lattice constant and the surface morphology correlated to the improved Tc and Jc.

By measuring the temperature dependence of the magnetoresistivity of Tl2Ba2CaCu2O8 thin films, two superconducting transitions were observed for field orientations in the H⊥ab- and H∥ab-planes. The transition at the high temperature (Tch) corresponds to a steep peak in the derivative of the effective activation energy and shifts very moderately with increasing magnetic field. The transition is in good agreement with the value of the upper critical field derived from critical fluctuation theory. Meanwhile, the transition at low temperature (Tcl) was associated with the Josephson coupling and strong intrinsic pinning for the two field orientations, respectively. This is consistent with the different magnetic field dependence of the activation energy calculated from the experimental data between Tch and Tcl.

Epitaxial c -axis-oriented HgBa 2 CaCu 2 O 6+ δ (Hg-1212) films ∼50–80 nm thick have been grown on (0 0 1) LaAlO 3 substrates using a cation-exchange process. These films show smooth surface morphology and high-quality epitaxy. The superconducting transition temperatures are up to 118 K. In zero applied magnetic fields, the critical current densities of these films are typically above 10 7 A/cm 2 at 5 K and remain up to 3.54×10 5 A/cm 2 at 100 K.

The effects of single-ion anisotropy and different sublattice transverse fields on the critical properties of the mixed Ising spin system on the square lattice are investigated within the framework of an effective field approximation. For certain values of the system parameters, tricritical points and reentrant phenomena can be observed, due to the competition between the different transverse fields and single-ion anisotropy. We present a detailed description of the phase diagram.

The magnetic properties of the nearest-neighbor interaction bond-diluted mixed ferrimagnetic spin system with crystal field are investigated by means of the effective field theory. Particular emphasis is given to the honeycomb lattice for which different magnetization curves are obtained. For certain bond concentration and negative crystal field values, the single or double compensation temperature may occur in the present system. We find a number of interesting phenomena that are not predicted by Neel theory. The influence of the bond concentration on the magnetization curves is discussed in detail in the paper.

The stability of the properties of Hg-based superconducting thin films has been studied during conventional photolithographic patterning processes. The patterning process was divided into individual steps such as photoresist baking, developing and etching in order to observe the effect of each step separately on the superconducting properties of the samples. After baking of the photoresist, a considerable degradation in the superconducting properties was observed, while samples did not show any visible degradation after they were etched with acid solution.

The dynamic magnetic hysteresis loops m(T, B a , B a ) of an epitaxial Tl2Ba2CaCu2O8 superconducting thin film are measured at various field sweep rates B a and at temperatures ranging from (1/2)Tc to (4/5)Tc. The magnetization current densities J m (T, B a , B a ) are obtained using the Bean model approximation. Followed by the determination of the maximum creep velocity for fluxons or flux bundles, the optimum temperature, current and field dependent functions of the effective activation energy, g(T), F(Jm) and Bγa are uniquely determined for a range of temperatures and applied fields. The inverse function of F(Jm), i.e. J c m (T, B a , B a ) , is in excellent agreement with the experimental results of J m (T, B a , B a ) . Hence in a range of temperatures and applied fields, the optimum temperature, current and field dependencies of activation energy can be ascertained without a priori assumption of their explicit forms.

Stability of Hg-based superconducting thin films has been studied in air, acetone, alcohol, water, and thermal cycling. T c , J c , and surface microstructures were analyzed as functions of exposure period. In dry air, fully reacted samples did not show degradation for a period of over one year, while samples which were not fully reacted due to air contamination or other reasons degraded within a few weeks. In humid air, samples were totally degraded within a few minutes. It has been found that the films degraded considerably in alcohol and acetone after they were immersed for a few hours, while this degradation was much severe in water. The mechanism of sample degradation has been discussed as well.

When the applied field B → a =μ 0 H → a parallel to the rotation axis of a disk-shaped superconducting thin film with radius R and thickness d in a cylindrical coordinate system, and the self-field effects of the screening current B → ′=B z ′ z +B ρ ′ ρ ( z ‖ B → a ⊥ ρ ) are considered, an effective method using finite-element analysis and matrix operation, to obtain the field dependent critical current function J c ( B ) from magnetic moment hysteresis loop m ( B a ) in a self-consistent way, is presented. Then also in a self-consistent way, the current density J ( ρ ) and field B z ( ρ )= B a + B z ′( ρ ) distributions can be obtained, regardless whether the film being fully penetrated by the applied field or not. The effects of the radial stray field B ρ ( ρ , z ) on the current cannot be neglected when B a ≈0. Due to the weak self-field effects, or intense demagnetic effects of the film compared with the long cylinder-shaped superconductor, between the average values of field 〈 B z 〉 and magnetization 〈 M 〉 there is a quantitative relation 〈 B z 〉= μ 0 [ H a +(0.8 d / R )〈 M 〉] for a disk-shaped film and a qualitative relation 〈B z 〉=μ 0 [H a +〈M〉/ 1+(2R/d) 2 ] for an arbitrary cylinder-shaped superconductor under the Bean model approximation.

The current density j{sub s} and relaxation rate Q have been measured on a ring shaped Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} film between 4.2K and the irreversibility temperature in magnetic fields up to 7T. The temperature and field dependent exponent {mu}(T,B{sub e}) used to parametrize the activation energy U in the form U(j{sub s},T,B{sub e})= (U{sub c}/{mu})[( j{sub c}/j{sub s}){sup {mu}}{minus}1] is determined for many different fields. In the B{sub e}{minus}T phase diagram we associate the {mu}=0 line with the glass temperature T{sub g} and find that T{sub g} essentially drops to 0K at B{sub e}{approx}0.7 T, which indicates a dimensional crossover at this field. The {mu}{gt}0 region (B{sub e}{lt}0.7 T, T{le}55 K) corresponds to 3D elastic vortex motin while the {mu}{lt}0 region corresponds to 2D dislocation mediated flux creep. {copyright} {ital 1997} {ital The American Physical Society}

The magnetic properties of the nearest-neighbor interaction mixed spin-1/2 and spin-1 Ising ferrimagnetic spin system with crystal field in a transverse field are investigated within the framework of the effective-field theory. Particular emphasis is given to the honeycomb lattice with coordination number Z = 3 for which magnetizations are obtained. If transverse field Ω varies in the certain ranges, we find that the compensation temperature is obtained for the value of the crystal field D in a restricted region. We discuss in detail the influence of the transverse field on the behaviors of the compensation point and magnetization curves in this paper.

The critical behaviour of the bond and site dilution transverse Ising model on a square lattice with spin - 1 2 is investigated within the framework of the finite cluster approximation (FCA). The phase diagrams, critical temperature, critical transverse field and percolation threshold are given. The FCA method is conceptually as simple as an ordinary mean field approximation (MFA) but gives much better results.

Tl 2 Ba 2 Ca 2 Cu 3 O x (TBCCO) thin films with T c ≥ 110 K were grown on the yttrium-stabilized (100) zirconia (YSZ) substrates by d.c. magnetron sputtering technique. The d.c.-SQUIDS made from the TBCCO films have operated at temperatures near 100 K. The relationship between I c and T of the grain boundary junctions is I ∞ (1 − T T c ) n , with n ≈ 1.6. This indicates that they are the long bridge junctions. The SQUIDs were biased by d.c. currents. Meanwhile, a 25 kHz a.c. flux with a peak-to-peak amplitude of φ 0 was applied through a modulation coil. The voltage across the SQUID was amplified by a factor of about 10,000 with a cooled transformer and a preamplifier. Our investigation showed that the d.c.-SQUIDs can operate near 100 K; some of them can even operate at 105 K.

Epitaxial Tl2Ba2CaCu2O8 thin films have been prepared on (001) LaAlO3 substrates by DC magnetron sputtering and a post-annealing process. X-ray diffraction (XRD) theta -2 theta scans, phi scans and rocking curves proved that the thin films are strongly textured with the c axis parallel to the c axis of the substrate and epitaxially grown on the substrate. A critical current density of 7.6*106 A cm-2 at 77 K has been obtained in zero magnetic field, and the films have strong flux pinning force in high magnetic fields. When magnetic fields were applied perpendicular to the Cu-O plane of the film, the critical current density dropped only by a factor of seven in a 4 T magnetic field and a factor of 15 in a 6.5 T magnetic field.