INCREASE OF T-N UP TO 190 K IN THE TYPE-II CMR MANGANITE PR1 2SR1/2MNO3/

Calcium doping of the type II CMR manganites Pr-1/2 Sr1/2MnO3 has allo wed the transition temperature T-N to be significantly increased up to 190 K. The systematic study of the solid solution Pr1/2Sr1/2-xCaxMnO3 shows that the mean size of the interpolated cation plays a prominent role in the CMR properties of these oxides: T-N increases significant ly whereas T-C decreases only slightly as the mean size of the interpo lated cation decreases, This behavior is fundamentally different from that observed for Pr1/2-xYxSr1/2MnO3 for which T-N increases slightly and T-C decreases dramatically as the mean size of the interpolated ca tion decreases. The rho(T) curves registered in a magnetic field of 7 T show a negative CMR effect characterized by a dramatic decrease of T -N and a complicated variation of the R(0)/R(H) ratio that reaches a m aximum value of 3 x 10(3) at 150 K in a magnetic field of 7 T for x = 0.09. (C) 1996 Academic Press. Inc.