Increase ofTNup to 190 K in the Type II CMR Manganite Pr1/2Sr1/2MnO3

Calcium doping of the type II CMR manganites Pr 1/2 Sr 1/2 MnO 3 has allowed the transition temperature T N to be significantly increased up to 190 K. The systematic study of the solid solution Pr 1/2 Sr 1/2− x Ca x MnO 3 shows that the mean size of the interpolated cation plays a prominent role in the CMR properties of these oxides: T N increases significantly whereas T C decreases only slightly as the mean size of the interpolated cation decreases. This behavior is fundamentally different from that observed for Pr 1/2− x Y x Sr 1/2 MnO 3 for which T N increases slightly and T C decreases dramatically as the mean size of the interpolated cation decreases. The ρ( 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 maximum value of 3 × 10 3 at 150 K in a magnetic field of 7 T for x = 0.09.