Strong spin-wave anomalies in La 1-x Sr x MnO 3 , x =0.125

The compound La0.875Sr0.125MnO3 exhibits a ferromagnetic phase below TC=181 K. At TO’O”=159 K, a magneto-structural transition occurs with spectacular properties. Extra Bragg peaks appear and, at related q-values, the spin-wave energies split and lock successively at the values of the different phonon modes. Moreover, in the long-wavelength range, two close spin-wave branches can be measured. They are characterized by two small gaps and similar stiffness constants. They have two distinct temperature behaviors. The lowest-energy branch seems to disappear at TO’O”.