Bernd T. Matthias

Rare-Earth Elements and High Pressures

Praseodymium, under very high pressures, shows a magnetic behavior similar to that of cerium at normal pressure.

High-Field, High-Current Superconductors

This article deals with superconducting materials which have zero electrical resistance while carrying high electrical current densities (around 106 amperes per square centimeter) in high magnetic fields (up to 50 teslas). The technological importance of these materials is due to their use in the windings of loss-free electromagnets which generate high magnetic fields. Such magnets are the foundation for superconducting electrotechnology, a rapidly growing field whose applications include advanced electrical machines and fusion reactors. The article focuses primarily on the materials aspects of this new techology. A brief overview is given of the physical principles which underlie this special type of superconducting behavior, and some of the important basic parameters are examined. The technology required to adapt the materials to electromagnets is also discussed. A few concluding remarks concern future possibilities for materials that can be used in generating very high magnetic fields.

Enhancement of Superconductivity through Lattice Softening

The superconducting transition temperature of an iridium-yttrium eutectic is enhanced extraordinarily through lattice softening. This is shown by a drastically reduced Debye temperature.

Superconductivity with Europium

Abstract EuIr 2 becomes superconducting at 0.2 K. Arc melting this compound raises T c to 2.6 K, in an apparently different and unidentified structure. These are the first superconductors containing Eu.

Weak itinerant magnetism as inhibited superconductivity

Thep-state pairing idea proposed recently to explain the ferromagnetism of ZrZn2 is described in more detail, and the underlying soft-mode hypothesis is examined in relation with experiments, in particular the discovery of antiferromagnetism in TiBe2. The key result, namely an electron-phonon contribution to the Stoner factor given essentially by the mass enhancement factorλ, is used to explain the behaviour of the Curie pointTm and to predict an isotope effect.p-state superconductivity with a transition temperature determined byλ is predicted in TiBe2 and, above the critical pressure whereTm=0, also in ZrZn2.

Superconductivity and the d-Shell

The various isotope effects on the superconducting transition temperature of Mo2B and W2B have been measured. Together with resistivity data they indicate that the d-shell forms a highly stable electron configuration for molybdenum and tungsten. This leads to an understanding of high superconducting transition temperatures.

Electrical resistivity and magnetic susceptibility of ThOs2

Abstract The temperature dependence of the electrical resistivity of ThOs 2 shows an unusual behavior. Anomalies in the magnetic susceptibility and low temperature crystal structure were sought but not found.

Hc2(4.2 K) of High‐Temperature Superconducting Alloys

Previous measurements of Hc2 versus T in selected Nb3Al1−xGex and Nb3Al alloys for dc magnetic fields to 200 kG and for 14 K ≤ T ≤ Tc have now been extended to 4.2 K by means of pulsed magnetic fields and rf measurements. Long pulse (10 msec) multipalyer coils producing fields to 450 kG were employed for the measurements. At 4.2 K, Hc2≃410 kG and Hc2≃320 kG for the highest Tc, Nb3Al1−xGex and Nb3Al alloys, respectively. These values of Hc2 are the highest measured for any superconductor. Measurements of Hc2 in several related alloys with somewhat lower values of Tc and Hc2 will also be presented. The large values of Hc2 (4.2 K) for all of these alloys permit great latitude of engineering design for practical wire materials. A summary of the physical properties of these high‐temperature superconductors, measurement techniques, present limits of high Hc2 materials, and a current appraisal of technical possibilities will be presented. A summary of some of the measurements has appeared.1

Ferroelectricity: Why did it take so long?

Abstract For many years, the ferroelectricity of first Rochelle salt, and then BaTiO3 appeared to be a very rare and isolated phenomenon. KDI and its isomorphs, discovered only after a seemingly exhaustive study of a great many different systems further enhanced the impression that ferroelectricity was one of Natures great accidents. With the discoveries of many new ferroelectric crystals having the preovskite or ilmenite structure, the superstition of there not being many ferroelectrics began to decrease somewhat. Strangely enough, in contrast to the study of other collective phenomena, serendipity never seemed to be much help. Finally, the discovery of GASH led to some of the alums, which in turn led to the discovery of ferroelectricity in ammonium sulfate, (NH4)2SO4. The ferroelectricity of (NH4)2SO4 had been overlooked or missed over the course of forty years of investigation. However, the impact of this reached further than just to (NH4)2SO4. It suggested the reexamination of hundreds of phase trans...

Abstract: Itinerant magnetism

Although, strictly, only ZrZn2 and Sc3In are intinerant ferromagnets, the phrase ’’itinerant magnetism’’ is used to describe all kinds of magnetism in metals containing well localized magnetic moments. Theoretical analysis of ZrZn2 has enabled the successful prediction of new itinerant magnets. (AIP)