Structural, electrical and magnetic properties of two-dimensional La-1.2(Sr1.8-xCax)Mn2O7 manganites

The effects of structural, electrical and magnetic properties with the isov alent chemical substitution of Ca2+ into the Sr2+ sites in La-1.2(Sr1.8-xCa x)Mn2O7 (x=0-0.8) are investigated. The highest magnetoresistance ratio [rh o(0)/rho(H)] of 208% (H = 1.5 T) at a temperature of 102 K was observed for the x = 0.4 sample. The Curie temperatures decreased from 135 to 102 K for x = 0-0.4, respectively. Moreover, the Weiss constants theta were varied f rom the positive to negative value with increasing Ca concentration. The an tiferromagnetic behavior with Neel temperature around 30 K was found in the x=0.8 sample. The magnetization measurements show that the hysteresis phen omenon appeared at the temperatures below the Curie or Neel temperatures. ( C) 1999 American Institute of Physics. [S0021-8979(99)06016-8].