Complex competition between ferromagnetism and antiferromagnetism in the CMR manganites Pr1-xCaxMnO3

The systematic investigation of the magnetic susceptibility of the CMR manganites Pr1-xCaxMnO3 versus temperature has been performed for 0.25 less than or equal to x less than or equal to 0.50. Due to the similar size of calcium and praseodymium, these results show the important role of the mixed valence of manganese upon the complex magnetic behaviour of these compounds. They demonstrate that the appearance of antiferromagnetism coincides with charge ordering, T-N = T-CO varying with x, from 250 K for x = 0.50 to 225 K for x = 0.35. A strong competition between ferromagnetism and antiferromagnetism is observed for 0.35 less than or equal to x < 0.50, starting from an antiferromagnetic state at high temperature (T > 170 K) and going through canted antiferromagnetic or weak ferromagnetic states for intermediate temperatures (70 K < T < 170 K). For 0.25 less than or equal to x less than or equal to 0.30, a strong ferromagnetic state is observed for 95 K less than or equal to T less than or equal to 150 K, with a transition to a spin glass like state below 95-110 K.