Giant magnetoresistance in mechanical alloyed La0.7Sr0.06Ca0.24MnO3 perovskite

Nanocrystalline ferromagnetic La0.7Sr0.06Ca0.24MnO3 perovskites have been successfully synthesized by mechanical alloying. The effect of grain size on magnetoresistance (MR) has been investigated. The results show that after milling for 100 h the as-made samples exhibit a complete amorphous phase, which crystallizes into a nanocrystalline perovskite-like compound when annealed above 920 K. With increasing annealing temperatures the grain size and the metal-semiconductor transition temperature increases, and the MR effect at 77 K decreases. The peak temperature T-p in MR behavior is found to be less affected by the grain size. All the annealed samples exhibit a larger MR at 77 K rather than around the temperature T-p. (C) 1998 Elsevier Science B.V. All rights reserved.