We study collective phonon excitations in SrTiO3 by low-frequency light scattering. We employ extended thermodynamics for phonon gas to construct a theoretical spectral function that is applicable regardless of local thermal equilibrium. Our analysis reveals the temperature dependence of tauN, the relaxation time for the momentum-conserving phonon collisions (normal processes), in SrTiO3. These results indicate that the previously reported anomalous soundlike spectrum originates from second sound, which is a wavelike propagation of heat.

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The activation volume (V,) and its correlation to media noise in high-density longitudinal recording media are investigated. Magnetization decay is observed to be non-linear with In(t) for the media studied, and the necessity for using a correct method for estimating a fluctuation field is emphasized. The activation volumes are shown to increase with decreasing reversing fields and the values of V, at low fields (of a few hundred Oe) are significantly higher than those at the coercivity. Thus, the collective behavior of the magnetic grains is influenced not only by the intergranular interactions but also by the stray fields. The media noise of different media is correlated to the V, values at low fields.