International audiencehfagnetic relaxation experiments constit.ute a unique method of determining the nature of fluctuations in dissipative magnetic systems. At high temperatures these fluctuations are thermal and strongly temperature dependent. At low temperatures, where quantum fluctuations dominate, magnetic relaxation becomes independent of temperature. Such behavior has been observed in many systems. In this review we emphasize the study of low temperature relaxation in ferromagnetic nanoparticles, layers, and multilayers (including " domain wall junctions "), and large single crystals. The results of magnetic relaxation experiments are shown to agree with theoretical predictions of quantum tunneling of the magnetization. When dissipation becomes important, in large and complex systems, a time dependent WKB exponent needs to be introduced

The electrical resistance of Bi and Bi-6 at.% Sb whiskers has been measured. Sample diameters were as low as 140 nm, lengths as large as 1.5 mm, and residual resistances as high as 165 k£2. Down to temperatures of 0.4 K, metallic behavior persists; the resistance R decreases with decreasing temperature T in contrast to other systems in which electron localization is invoked to explain negative dR/dT's.

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We have obtained a thermodynamic state of thin helium films which permits precision measurements of their properties. Third-sound resonances indicate a cutoff for the propagation of third sound in these films. This cutoff is accompanied by an exponential rise in the dc thermal resistance of the helium film which indicates the formation of high-energy excitations of 0.08 eV. The dissipation at resonance is consistent with Bergman's theory for hydrodynamic dissipation of third sound.

A dc electric current is injected through the transverse normal-metal strip of Ag-Sn proximity-effect bridges to generate phonons which propagate through and further weaken the superconductivity in the proximity-effect-induced weak region by creating quasiparticles (by pair-breaking mechanisms}. Consequently a decrease of the critical-current hysteresis is observed in the current-voltage characteristics of these bridges. These results cannot be adequately accounted for by simple heating. Further, we find that Parker's modified heating theory of nonequilibrium superconductors has to be invoked for a qualitative understanding of the observed phenomena.