T.L. Francavilla

Magnetic Susceptibility of Superconductors and Other Spin Systems

Basic Experimental Techniques and Concepts: Multipurpose Cryostat for Low Temperature Magnetic and Electric Measurements of Solids (C. Rillo et al.). ac Inductive Measurements (Q.Y. Chen). Theoretical Considerations and Phenomenological Models: ac Losses in Type II Superconductors (J.R. Clem). Bulk and Single Crystal Samples: NonLinear ac Susceptibility Response Near the Irreversibility Line (L. Civale et al.). Thin Films: ac Susceptibility Techniques Applied to Thin Film Superconductors (J.H. Classen). Magnetically Ordered and SpinGlass Systems: ac Susceptibility of Dilute Magnetic Systems (G. Williams). Specialized Measuring Techniques: Magnetically Modulated Resistance Techniques (B. Kim et al.). AppendixIrreversibility Line Debate. 26 additional articles. Index.

Superconducting properties of reactively sputtered NbCN thin films

Niobium Carbonitride thin films have been prepared by rf reactive sputtering of niobium in ar argon, reactive-gas (RG) atmosphere where the RG is a mixture of cyanogen and nitrogen. Film composition ranged from Nb 1 C x N 1-x ( 0.03\leq \times \leq0.5 ) as determined by Auger analysis, the carbon content roughly tracking the cyanogen partial pressure. Composition and substrate temperature were systematically varied and the resultant films studied by measurements of x-ray structure, resistivity, superconducting transition temperature T c , and critical magnetic fields. We have found systematic preferential orientation of the crystallites in these films depending upon substrate temperature ana RG to argon ratio. Increasing either quantity causes the crystallites to reorient from the

Giant resistivity and X-ray diffraction anomalies in low-dimensional ZrTe5 and HfTe5

Abstract Two giant anomalies have been observed in single crystal samples of metallic ZrTe 5 and HfTe 5 : one is an extremely large maximum in the electrical resistivity at low temperature and the other is a correspondingly large maximum in the intensities of certain “forbidden” x-ray reflections, which correlate in temperature with the electrical anomaly.

Core-loss analysis of an (Fe, Co, Ni)-based nanocrystalline soft magnetic alloy

Nanocrystalline soft magnetic materials possess higher magnetization and operation temperatures than amorphous alloys with similar compositions. For these reasons, they are good candidate materials for power electronics applications. As an indication of their performance, core losses have been measured for a nanocrystalline alloy with the composition Fe64.08Co10.68Ni10.68Zr8.49B4.86Cu1.2 synthesized by a melt-spinning process with subsequent isothermal anneal at 550°C for 1h. The experiments were conducted on toroidal samples using a Walker ac permeameter over a frequency range of 100Hz–500kHz, at induction amplitudes of 100 and 1100mT, at room temperature. A measured toroidal sample possessed a saturation magnetization of 1.529T and core loss of 17.5W∕kg at a frequency of 10kHz and magnetic flux density of 100mT. The Steinmetz analysis of the static hysteresis losses yielded a power-law coefficient of 1.475. A statistical model for excess eddy current losses showed good agreement with experimental result...

(Ni,Fe,Co)-based nanocrystalline soft magnets with near zero magnetostriction

Nanocrystalline soft magnetic materials have been developed possessing a wide variety of compositions designed to reduce losses and a high saturation induction. Nanocrystalline soft magnetic alloys with compositions (Fe/sub 1-x-y/Co/sub x/Ni/sub y/)/sub 89-z/Zr/sub 7/B/sub 4/Cu/sub z/ were prepared by the isothermal annealing of melt-spun ribbons. The ribbon samples were characterized by the following techniques: differential thermal analysis, X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometry. Several alloys have been shown to have near-zero magnetostriction. Alloy design, synthesis, and properties of these alloys will be discussed.

Multifilamentary V 3 Ga wire: A critical review

Initial studies of V 3 Ga conductors formed by the bronze technique coincided with early work on Nb 3 Sn conductors; however, due to several technological difficulties, emphasis to date has been on commercial production of Nb 3 Sn composites. The superior critical current density of V 3 Ga in high magnetic fields (H> 10T), however, favor this conductor in selected applications. Improvements in critical current density have been achieved by using a modified bronze technique whereby the filaments as well as the Cu matrix are alloyed with Ga. Recent studies of the temperature and magnetic field dependence of the critical current density as well as stress effects, and third element additions are presented. Superconducting applications which may benefit from the use of V 3 Ga wire will be emphasized.

Observation of a transverse voltage in the mixed state of YBCO thin films

The occurrence of a transverse voltage peak has been observed in YBCO thin films. This phenomenon occurs under conditions of temperature and current in the earths magnetic field such that the films are in the mixed state. The magnitude of the peak was found to scale with both temperature and current, and exhibited a Sin(/spl theta/) orientational dependence measured between the film-substrate and the position of the measurement electrodes on the film surface. These observations are similar to observations made in conventional superconducting thin films such as Nb, NbN, NbCN, and PbBi.<<ETX>>

Microstructural and superconductive studies of Ag-YBa2Cu3O7−x composites

Composites of Ag-YBa2Cu3O7−x were synthesized and carefully characterized for crystal structure and microstructure by X-ray diffraction, optical microscopy, SEM, TEM, and EDAX techniques in order to investigate the effect of Ag additions on the superconducting properties of 123 compounds. The a.c. susceptibility data show thatTc (onset) of 123+Ag composites vary between 90.2 and 91.8 K. TheJc values we measured for 123 material without silver were in the range of earlier reported values for the pure 123 material. Whereas there is a relatively small increase in the critical current for the YBCO/Ag2O ratio of 3, the variation of the grain size of the composites shows that theseJc changes are due to slight variations in the grain size rather than any dramatic effect of Ag inclusions as speculated earlier.

Formation of the structure of the superconducting phase of La-Sr-Cu-O by DC sputtering

Abstract DC sputtered film samples of La-Sr-Cu are found to be noncrystalline. Annealing in air at temperatures as low as 350°C yields crystallization of the structure of the superconducting phase of La-Sr-Cu-O. We present X-ray spectra showing the continuous development of the La-Sr-Cu-O phase and a decrease in the c / a ratio upon further annealing in air for temperatures up to 600°C.

Mixed‐state behavior in large magnetic fields of high‐temperature superconducting films prepared by metalorganic deposition

Films of Ba2YCu3O7−x prepared by metalorganic deposition (MOD) are demonstrated to have large critical current densities in high magnetic fields. The current‐voltage (I‐V) characteristics are reported for an MOD film in applied fields from 0 to 6 T at 77 K. The zero field critical current density was 600 000 A/cm2 and fell to 60 000 A/cm2 at 1 T. The critical current is approximately proportional to 1/H1/2. The variation in I‐V curves above the critical current indicates the voltage has a power law behavior with values for the current exponent varying from 5.2 to 1.7 for magnetic fields from 0 to 6 T.