Magnetic phase diagram of oxygen isotope-substituted Pr0.7Ca0.3Mn16–18O3

Magnetisation and susceptibility measurements have been performed on the oxygen isotope-substituted manganite Pr0.7Ca0.3Mn16–18O3 in pulse magnetic fields up to 35 T in the temperature range 78–300 K. It was found that the charge-ordering transition temperature <f>TCO&ap;210</f> K and temperature of antiferromagnetic ordering <f>TAFM&ap;125</f> K in this narrow band manganite are independent on isotope content. The magnetic-field-induced transition into ferromagnetic state was observed in both isotope-substituted samples at temperatures TFM. Isotope substitution has been proved to have a significant impact on the critical field HC of this transition. We found that magnetisation curves are qualitatively different for both isotopic samples. The sample with natural oxygen has the positive derivative dHC/dT on the whole T–H plane. In compound with 18O, HC is shifted to the higher fields (HC∼20 T), being nearly temperature-independent at <f>T>120</f> K. As the temperature decreases (<f>T<TAFM</f>), this transition disappears and a more complicated behaviour arises at magnetic fields 6–14 T. [Copyright &y& Elsevier]