The colossal magnetoresistance of (La1-yTby)(2/3)Sr1/3MnO3 perovskite

A series of polycrystal bulk samples of (La1-yTby)(2/3)Sr1/3MnO3 (x = 0, 0. 05, 0.15, 0.20, 0.25, 0.33, 0.4, 0.5, 0.6, 1.0) have been prepared. Their m icrostructrues, magnetization M, resistance R as well as magnetoresistance (MR) have been systemicallly studied in the temperature range 10 K less tha n or equal to T less than or equal to 420 K The ferromagnetic: transition t emperature of the samples T-C decrease with the increase y. For each sample , R have peak values at a temperature close to T-C. The peak values of R in crease rapidly with increasing y. At the sample (y = 0.40), a colossal magn etoresistance up to 900% has been observed on the temperature 170 K.