NEW ADVANCED MATERIALS OF La_(1.2)(Sr(1.8-x)Ca_x)Mn_2O_7 WITH COLOSSAL MAGNETORESISTANCE

摘要

The effects of structural, electrical and magnetic properties with the isovalent chemical substitution of Ca~(2+) into the Sr~(2+) sites in new series of the La_(1.2)(Sr_(1.8-x)Ca_x)Mn_2O_7 compounds (x = 0 ～ 1.8) are investigated. The highest magnetoresistance (MR) ratio [ρ(0)/ρ(H)] of 208 % (H = 1.5 T) at a temperature of 102 K was observed for the x = 0.4 sample. The static strain within the compound for x = 0.4 has also been found by high resolution transmission electron microscopic techniques. The Curie temperature decreases with Ca doping from 135 K to 71 K for x = 0 to 0.8 and from 355 K to 260 K for x = 1.2 to 1.8 respectively.