Unusual magnetic relaxation behavior in La0.5Ca0.5MnO3

We present an extensive study of the time dependence of the magnetization in a polycrystalline and low temperature charge ordered La0.5Ca0.5MnO3 sample. After application and removal of a 5 T magnetic field, a systematic variation of the magnetic relaxation rate from 10 K to 245 K was found. At 195 K, the magnetization decreases in a very short time and after that it increases slowly as a function of time. Moreover, between 200 and 245 K, an increase in magnetization, above the corresponding value just after removing the 5 T magnetic field, was measured. This unusual behavior was tested in several other relaxation procedures. PACS: 70, 74.25 Ha, 75.60.-d, 76.60.Es