High-temperature elastic measurements in La2/3Sr1/3MnO3 at low frequency

In the present work, we report elastic measurements performed on the mangan ese perovskite La2/3Sr1/3MnO3, for which the ferromagnetic ordering tempera ture was determined to be 377 K. coincident with a metal-insulator transiti on. Measurements in the temperature range 250-480 K at various frequencies were performed, showing a weak dip in the modulus (1.9%) and no Q(-1) peak at the magnetic transition, unlike La-2/3 Ca-1/3 MnO3. Two Q(-1) peaks were observed, one above T-c (414.5 +/- 0.2 K at 1 Hz) and another below T-c (3 03 +/- 6 K at 1 Hz). With increasing measurement frequency between 0.3 and 20 Hz. a shift to higher temperatures of the centers of both peaks was obse rved. Such shifts yielded an activation energy of 3.77 +/- 0.05 eV for the high-temperature peak and 0.56 +/- 0.07 eV for the low-temperature peak. Ev idence was found that the high-temperature peak is not a simple relaxation process, but shows a relaxation time distribution. Relaxation peaks are att ributed to jumps of oxygen ions within the crystal under applied stress. (C ) 2001 Elsevier Science B.V. All rights reserved.