Semiconductor–metal transition, thermoelectric power and giant magneto resistance of the double Mn perovskite-La1.5Ca1.5Mn2O7

In La 1.5 Ca 1.5 Mn 2 O 7 , whereas a ferromagnetic transition was observed at T c ∼200 K, the resistivity data revealed a semiconductor–metal transition at 95 K, much lower compared to T c . However, thermoelectric power data indicated a strong decrease in carrier density around T c with no detectable anomaly at 95 K. Magneto resistance −( R H − R 0 / R 0 ) plots taken in H =5 T revealed two maxima one with a value of about 95% at 100 K and another of 30% at 200 K.