Structural, electrical and magnetic properties of two-dimensional La1.2(Sr1.8−xCax)Mn2O7 manganites

The effects of structural, electrical and magnetic properties with the isovalent chemical substitution of Ca2+ into the Sr2+ sites in La1.2(Sr1.8−xCax)Mn2O7 (x=0–0.8) are investigated. The highest magnetoresistance 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 Curie temperatures decreased from 135 to 102 K for x=0–0.4, respectively. Moreover, the Weiss constants θ were varied from the positive to negative value with increasing Ca concentration. The antiferromagnetic behavior with Neel temperature around 30 K was found in the x=0.8 sample. The magnetization measurements show that the hysteresis phenomenon appeared at the temperatures below the Curie or Neel temperatures.