W. Schön

Acoustic and Magnetic Studies of an Insulating Spin Glass

a.c. magnetic-susceptibility measurements show that a cobalt fluorophosphate glass enters a spin glass below Tf 1.8 K. Acoustic measurements in zero magnetic field reveals a frequency-dependent dip in the relative velocity change and an excess attenuation in the vicinity of Tf. A four-spin correlation function is deduced: it presents a maximum near Tf, while the relevant relaxation time has no anomaly at this temperature.

High-frequency dielectric study of the dynamics of (KBr)1−x(KCN)x mixed crystals

Dielectric measurements have been performed at 1 and 10 GHz in (KBr)1−x(KCN)x mixed crystals for cyanide concentrationsx=0.25 andx=0.50 in the temperature rangeT=1.7–150 K. The maxima of the real and imaginary parts of the dielectric constant falls into the Arrhenius straight lines obtained at lower frequencies. These dipolar lines cross over the so-called quadrupolar (acoustic) lines, in contradiction with theoretical predictions on the nature of the freezing. We also present a qualitative model which reinterprets the dipolar and quadrupolar freezings in terms of an individual and a collective processes.

Nuclear acoustic resonance in an insulating manganese spin-glass

Nuclear-acoustic-resonance experiments on an insulating manganese fluorophosphate spin-glass are reported. They provide information on the distribution, P(S), of the mean local magnetization experienced by the 55Mn nuclei in the spin-glass phase.