Silver-sheathed BiPbSrCaCuO wires were fabricated using the powder-in-tube method. Critical current densities at 77.3 K were 4.7*10/sup 4/ A/cm/sup 2/ in a zero magnetic field, 3.1*10/sup 4/ A/cm at 0.1 T, and 1.1*10/sup 4/ A/cm/sup 2/ at 1 T. In liquid He, these wires can carry 1.03*10/sup 5/ A/cm/sup 2/ at 23 T. J/sub c/ and J/sub c/-B enhancements are due to grain-boundary improvements. Detailed investigation of J/sub c/-B characteristics in magnetic fields, especially increasing and decreasing fields, revealed that history effect behaviours caused by weak links disappeared with improvements of grain-boundary characteristics at both temperatures. It was observed that 1296 multifilamentary wires were capable of sustaining over 70% of J/sub co/ even after a strain of up to 0.66% repeated 10 times. Prototypes of coils and current leads were fabricated using 20-m-long wires. One coil showed critical currents of 54.2 A at 77.3 K and 367 A at 4.2 K. This coil generated a B/sub m/ of 142 G at 77.3 K and 876 G at 4.2 K. A prototype of a react & wind-processed coil was demonstrated using greater than 4-m-long multifilamentary wires, and it successfully produced enough magnetic field to rotate copper windings between steel cores.

High-J/sub c/ silver-sheathed Bi-based superconducting wires

Amorphous metals have magnetomechanical properties superior to those of crystalline magnetostrictive materials, and are therefore being considered for a variety of transducer and sensor applications. A simplified model is presented of magnetomechanical coupling in amorphous metal ribbons, showing the relation between magnetomechanical behavior and fundamental material parameters. Although high values of magnetization and magnetostriction are important, it is primarily the low values of magnetic anisotropy achievable that give amorphous metals their outstanding magnetomechanical coupling. The magnitude and homogeneity of this anisotropy is controllable through choice of alloy composition and annealing conditions.



Amorphe Metalle haben bessere magnetomechanische Eigenschaften als kristalline Werkstoffe, und werden deshalb fur Anwendungen als Energieumwandler und Kraftubertrager betrachtet. Ein vereinfachtes Modell der magnetomechanischen Kopplung in amorphen metallischen Bandern wird gegeben, das die Beziehung zwischen magnetomechanischem Verhalten und grundlegenden Parametern des Werkstoffes erkart. Obwohl hohe Werte der Magnetisierung und Magnetostriktion wichtig sind, stammen die hervorragenden magnetomechanischen Kopplungseigenschaften in amorphen Metallen hauptsachlich von den niedrigen Werten der magnetischen Anisotropie. Die Werte und die Homogenitat der Anisotropie werden durch die Legierungszusammensetzung und die Anlasbedingungen kontrolliert.

Magnetomechanical properties of amorphous metals

Vue d'ensemble sur la preparation, la caracterisation, les proprietes de transport et les proprietes magnetiques des superreseaux

Artificial metallic superlattices

The structural ageing characteristics of aluminium alloys containing 2 and 4 wt.-% lithium are reported. One transition phase (AI3Li, δ′) occurs in the alloy system and time-temperature-transformation curves have been determined for this phase and the equilibrium precipitate. Strengthening in these alloys is associated with δ′ precipitation, the peak hardness increment occurring in the 2% alloy after ageing for 24 h at 200°C (473K). Thin-film electron microscopy was used to confirm the ordered L12-typestructure of the δ′ and to study the precipitate size and distribution over a range of ageing temperatures. At low temperatures the δ′, which has a spherical morphology, is very fine (∼ 0.01 μm at 100°C, 373K) and resists coarsening. Above 200°C (473 K) coarsening is rapid and the process has been analysed using the Lifshits-Wagner theory. The δ′ interfacial energy was estimated to be ∼ 240 erg/cm2 (0.24 J/m2) and the lattice mismatch 0.18%. At and below 60°C (333K), ageing is accompanied by an incre...

Precipitation Characteristics of Aluminium-Lithium Alloys

The structure and properties of Co–N and Co–O based films, prepared by rf magnetron reactive sputtering using nitrogen or oxygen and argon gases, have been studied. Transmission electron microscopy (TEM) observation reveals that each Co–(Al or Si)–(N or O) film is a typical film with granular structure, with grain size less than 5 nm. It is found by micro‐focused energy‐dispersive x‐ray and electron energy loss spectroscopy analysis that the grains are mainly composed of Co and the intergranular regions are ceramics of N or O. In Co–N based films, soft magnetic properties are found in both Si and Al containing films over a wide range of film preparation conditions and compositions. Only the films with Al show soft magnetic properties in Co–O based films, which have ρ of 500–1000 μΩ cm, Hk of about 80 Oe and Bs of about 10 kG. By adding about 10 at. % Pd, the soft magnetic properties and Hk of Co–O based films are significantly improved, with Hk more than 180 Oe. These films exhibit a remarkable constant f...

High‐frequency magnetic properties in metal–nonmetal granular films (invited)

Anisotropy and hysteresis of transport critical currents in high temperature Ln-Y-Ba-Cu-O superconductors

For new magnetic materials with high permeability at MHz frequencies as well as high magnetic induction, magnetic properties of Co‐base amorphous alloys produced by a sputtering technique were investigated. Small magnetostrictions, important for this purpose, were found in the Co‐Nb‐Ti system and Co‐(Fe, Mn)‐Nb system. The dipole‐type model explained the concentration dependence of magnetostriction. In order to increase permeability at high frequencies by reducing eddy current losses, these amorphous alloys were made into thin film form. It was found that dc coercivity for the single film (about 3 μm thick) of Co80 Nb20 with negative magnetostriction was larger than that for Co80Ti20 with positive magnetostriction, while the layered films of Co80Nb20 separated by a SiO2 insulator showed small coercivities. Permeabilities of about 4×103 at 1 MHz and 1×103 at 10 MHz were obtained in the Co80Nb20/SiO2 and Co80Ti20/SiO2 layered films.

Magnetostriction of Co-base amorphous alloys and high frequency permeability in their sputtered thin films (invited)

Compositional dependence of the magnetically induced magnetic anisotropy in the Fe and Co based amorphous alloys has been studied experimentally. The induced anisotropy constant is 30–60 erg/g for Fe78Si10B12 and for Co78Si10B12 but is 400–500 erg/g for (Fe1−xCox)78Si10B12 in 0.25<x<0.8. The addition of elements such as Ni, Pd and Cr into Co78Si10B12 results in the increase in induced anisotropy constant. The directional order of metal-metal pairs is most likely to be responsible for the induced anisotropy.

On the Magnetically Induced Anisotropy in Amorphous Ferromagnetic Alloys

The effects of underlayer materials Cr, Ti, V and Cu on the magnetic properties such as coercivity and the microstructure of Co/sub 85/Sm/sub 15/ films deposited onto these underlayers were investigated. A coercivity as high as 3600 Oe was obtained in the Co/sub 85/Sm/sub 15/ film with a 100 nm thick Cr underlayer, but it was about 1800-2600 Oe in the cases of Ti, V and Cu underlayers with the same thicknesses. Cross-section TEM observation revealed that a clear columnar structure is formed for the Cr underlayer but not clearly for the other underlayers. High resolution TEM observation indicated that the CoSm film with Cr underlayer consists of amorphous columns and crystalline boundaries surrounding those columns. It was considered that this heterogeneous structure gives rise to the large coercivity in the case of the Cr underlayer. >

Magnetic properties and microstructure of sputtered CoSm/X (X=Ti, V, Cu and Cr) thin films

Transmission electron microscopy and diffraction study and electrical resistivity measurement of iron-aluminium alloys containing 17.87 to 21.54 at.% aluminium have revealed the nature of the “ K -state” in this alloy system. It has been conclusively demonstrated by the observations of dark field images that the so-called “ K -state”, which appears on annealing at a low temperature after quenching from a high temperature, is characterized by the inhomogeneous formation of very small Fe 3 A1 type ordered particles of 20∼30A in diameter in the matrix α-solid solution. The specimens slowly cooled from a high temperature and isothermally annealed have also been examined to compare the structures with those showing the “ K -state”. A discussion on the equilibrium phase diagram of the iron-aluminium solid solution is given.

Hiroaki Morita

Papers

Anisotropy and hysteresis of transport critical currents in high temperature Ln-Y-Ba-Cu-O superconductors

Magnetostriction of Co-base amorphous alloys and high frequency permeability in their sputtered thin films (invited)

On the Magnetically Induced Anisotropy in Amorphous Ferromagnetic Alloys

Magnetic properties and microstructure of sputtered CoSm/X (X=Ti, V, Cu and Cr) thin films

Transmission Electron Microscopic Study on the “K-State” in Iron-Aluminium Alloys