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Twenty years ago magnetism and superconductivity appeared mutually exclusive and life was (relatively) simple. The discovery of heavy-fermion superconductivity (1979-1984) and high T(c) (1986), changed our perceptions. Gradually, it was realised that either ordered magnetism or magnetic correlations are found in most of these materials. Here I shall concentrate on heavy fermions, in which the f electrons are responsible for the magnetism as well as (probably) the superconductivity. Muons have played a key role in elucidating these the so-called "small moment" systems, such as UPt(3), Uru(2)Si(2), UPd(2)Al(3), etc. Recenty, at the ILL we have measured the low-energy inelastic magnetic signal from Upd(2)Al(3) and the response will be compared to the conclusions derived from muon studies. Interestingly, it is accepted wisdom that muons will be sensitive to any small magnetic effects. UBe13 is fascinating as it has long been the "exception", with no sign of any magnetism. Now, at Riso National Laboratory, we have found evidence with neutrons for weak magnetic correlations of a most unusual form in Ube(13) -so that it no longer can be regarded as an exception. Neutrons, powerful though they are, are sometimes lost in reciprocal space. U(2)Pt(2) In is a non-Fermi liquid, and there is a strong muon anomaly below 10 K, but we have been unable to find the correlations with neutrons. Finally, NpO(2) is one of the oldest "small-moment systems", and recently muons were able to see an asymmetry below 25 K, and suggested an ordered moment of 0.1ý(B). However, the signal has been too small for neutrons. Here I will explain the emergence of a new technique, resonant magnetic X-ray scattering, that, especially in the actinides, has great promise. We have used this at the ESRF to determine the magnetic structure of NpO(2).

Additional information

Authors: LANDER G.H, ITU, Karlsruhe (DE)
Bibliographic Reference: Article: Elsevier, Physica B 285-290 (2000) pp: 1-9; Oral Report: 8th International Conference on Muon Spin Rotation, Relaxation and Resonance, Les Diablerets (CH), 30 August- 3 September
Availability: 1 as paper EN 60681 ORA
Record Number: 200012845 / Last updated on: 2000-11-07
Original language: en
Available languages: en
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