We observed a magnetization step accompanied by a metal-insulator transitio
n around 75 K in La0.5Ca0.5MnO3. Repeating measurements under the same cond
ition weaken the magnetization step and enhance the resistance at low tempe
rature. The decayed magnetization step reappears after annealing the sample
at high temperature or cooling it under a magnetic field. The low-temperat
ure magnetization step can be attributed to the melting of the overcooled f
erromagnetic fragments and its training effect may be related to structure
distortions at the interfaces between the ferromagnetic and charge-ordered
phases in the investigated system.