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Magnetization measurements have been performed on samples composed of oriented YBa 2 Cu 3 O 7 single crystals 1.4 K, 68 K and 78 K in magnetic fields up to 38 T applied along the c -axis and within the ab -plane. The critical currents are deduced from the irreversible magnetization and discussed in terms of pinning forces. At low temperature (1.4 K), the experimental data with the field along the c -axis are compared with a theoretical model for the field dependence of the pinning force. At higher temperatures (68 K and 78 K), the pinning force can be described by a Kramer-like scaling law: F p = A [ B 0 ( T )] m b p (1− b ) q , where B 0 is the field where the irreversibility of the magnetization disappears and where b (= B / B 0 ) is the reduced field. For the exponent m , the usual value of 2.5 is found; approximate values for p and q are around 2 and 4, respectively.

Two constraints on semi-continuous magnet coils are the strength of the winding material, and the maximum power which the rectifier must deliver for a short time. Here we assume that for a 60-T coil wire of sufficient strength (about 100 kg/mm2 is available. It was shown earlier that a single, homogeneous coil needs a power of nearly 150 MW, which calls for huge capital investments in power lines, transformers, switches and rectifiers. By using two nested coils, wound from wires with different strengths and current densities, and energized successively by the same rectifier, we can reduce the power to less than 50 MW.

The zero-field moment of Tb has been determined at 4.2 K for a very pure single crystal along the b direction. A value of (9.490 ± 0.010) μ B /at was found. The corresponding conduction electron polarization of 0.519 μ B /at is much higher than previously estimated. The conduction electron susceptibility was found not to be at variance with the value obtained from band calculations. No agreement is found for the field dependence of the magnetization at 64.5 K and 77 K with a renormalized spin wave theory although the differences are small.

A sample of YBa 2 Cu 3 O 7 was constructed by stacking a number of small single crystals. Magnetization measurements were made in magnetic fields up to 38 T, both parallel to the c -axis and to the basal plane. At 1.4, 4.2 and 20.4 K, a large irreversible magnetization was observed. The significance of these results for the superconducting properties is discussed.

The magnetization of high- T c superconducting REBa 2 Cu 3 O 7 compounds, where RE is Y or one of the rare-earth elements Eu, Gd, Dy, Ho, Er or Yb, has been measured in fields up to 29 T. Though the precise analysis of the data is hampered by the incomplete penetration of the magnetic field due to the shielding-current effect of the superconductivity, the magnetism associated with the rare-earth ions can reasonably be interpreted by crystal-field effects. All of the samples investigated were confirmed to be superconducting at 4.2 K in fields as high as 29 T.

The University of Amsterdam has a semicontinuous magnet in operation, which can generate fields up to 40 T and keep these fields constant (within 1:10/sup 4/) during 0.1 s for 40 T, and longer for lower fields. The authors discuss a project for the establishment of a 60-T 100-ms facility primarily based on the concept of the present 40 T 100-ms magnet with its controlled power supply, which makes, within certain limits, any desired field profile possible. A Cu-Be mantle with a core of pure Cu is the most-suitable candidate for the wire material of the 60 T coil. The power supply, rectifier, transformers, and thyristors needed are described. The prospects for the fulfilment of the design are briefly mentioned. >

An overview is given of the high-field installation of the University if Amsterdam now in operation; this installation can generate fields up to 40 T, constant within 8 mT for about 80 ms. Recent improvements of the regulation of the field are discussed, as well as some examples of recent measurements.

Magnetization measurements in pulsed magnetic fields up to 40 T at 1.3, 67 and 78K have been performed on a 50 mg sample composed of 45 aligned single crystals of YBa2Cu3O7. Data have been obtained with the applied field both parallel and perpendicular to the c axis. The results are compared with dc magnetization measurements on the same sample. At high temperature a strong dependence on the field sweep velocity is observed. The results are discussed in terms of flux pinning and thermally activated flux-flow.

Hall-effect of single-crystalline UPt 3 and U(Pt 0.95 Pd 0.05 ) 3 was measured in magnetic fields up to 38 T. At all investigated temperatures R H is found to decrease with increasing field; at 1.4 and 4.2 K a large peak is found that is attributed to the suppression of antiferromagnetic correlations.