No abstract

Using a diamond-anvil cell, we have probed the pressure-induced rutile-to-CaCl 2 ferroelastic phase transition in RuO 2 with Raman spectroscopy. The transition is marked by a splitting of the degenerate E g mode of the rutile phase into two nondegenerate components and by an abrupt change in the Grüneisen parameters for all the phonons. The behavior of this splitting shows good agreement with Landau's theory for a second-order phase transition, application of which yields a transition pressure of 11.8Ϯ0.3 GPa. ͓S0163-1829͑97͒03326-2͔

Raman spectra of NiPS& (spin S =1) reveal an anomalously broad two-magnon feature whose relative width is comparable to that shown by La2CuO& (S = 2) and other antiferromagnetic copper oxides. The magnetic continuum is strongly coupled to a nearby phonon, whose scattering amplitude interferes with

The time evolution of the line charge density and energy at the ends of an initially rectangular ion bunch due to the space charge of the bunch are measured and found to be in good agreement with a one-dimensional dynamical theory. The ends erode at the space-charge wave speed into the bunch, and the end particles move at twice that speed away from the bunch.