Longitudinal sound velocity and internal friction in ferromagneticLa1−xSrxMnO3single-crystal manganites

Abstract

We have studied the temperature dependence of sound velocity and internal friction in ferromagnetic ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ single crystals, $x=0.15,$ 0.20, and 0.25, grown by the floating zone method. The sound velocity and internal friction were determined by the composite oscillator method at frequencies of order 100 kHz. The compositional metal-insulator transition has been found to be accompanied by an increase of the sound velocity and a weakening of its temperature dependence. It is likely that ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{MnO}}_{3}$ undergoes a transition between the O* phase and an unknown phase at about 60 K. In ${\mathrm{La}}_{0.80}{\mathrm{Sr}}_{0.20}{\mathrm{MnO}}_{3},$ a weak transition of the first order occurs at 400 K. It has been revealed that the giant thermal hysteresis of sound velocity and internal friction is the specific feature of the $\mathrm{Pnma}\ensuremath{-}R3\ifmmode\bar\else\textasciimacron\fi{}c$ transition; therefore, in a wide temperature range there is the mixture of these crystalline phases. Above 400 K, relaxation peaks of the internal friction due to point defects have been found.