Colossal magnetoelastic effects at the phase transition of (La sub(0.6)Pr sub(0.4)) sub(0.7)Ca sub(0.3)MnO sub(3)

(La sub(0.6)Pr sub(0.4)) sub(0 .7)Ca sub(0.3)MnO sub(3) was characterized by means of ultrasound velocity and attenuation to study the temperature and magnetic field dependence of the elastic constants and to gain an insight into the metamagnetic transition. The metal-insulator and ferromagnetic-paramagnetic transitions are reflected in the behavior of the elastic constants due to strong electron-phonon and spin-phonon interactions. A hysteresis in elastic behavior and metamagnetism hints toward first-order nature of the phase transition. A softening of bulk modulus at the ferromagnetic transition for magnetic fields [mu] sub(0)H > 2 T was attributed to a coupling between the lattice and spin fluctuations. This softening peaks at a certain temperature T* approximately 215 K and field [mu] sub(0)H* approximately 4 T, which could be an indication of a critical end point of the ferromagnetic transition.