Time dependent effects and transport evidence for phase separation in La0.5Ca0.5MnO3

The ground state of La1-xCaxMnO3 changes from a ferromagnetic metallic to a n antiferromagnetic charge-ordered state as a function of Ca concentration at x similar to 0.50. We present evidence from transport measurements on a sample with x=0.50 that the two phases can coexist, in agreement with other observations of phase separation in these materials. We also observe that, by applying and then removing a magnetic field to the mainly charge-ordere d state at some temperatures, we can "magnetically anneal" the charge order , resulting in a higher zero-field resistivity. We also observe logarithmic time dependence in both resistivity and magnetization after a field sweep at low temperatures. (C) 2000 American Institute of Physics. [S0021- 8979(0 0)42808-2].