Cation size-temperature phase diagram of the manganites Ln(0.5)Sr(0.5)MnO(3)

We have studied the variation of the paramagnetic to ferromagnetic transition temperature T-C and of the ferromagnetic to antiferromagnetic transition temperature T-N as a function of the average size of the A site cations (Ln, Sr) in the manganite perovskites Ln(0.5)Sr(0.5)MnO(3) (Ln=Gd, Sm, Y, Pr, La). For our investigation we used dc resistivity, magnetization, susceptibility and magnetoresistance measurements. Results show that the Curie temperature T-C increases from 85 to 310 K when [r(A)] varies from 1.221 to 1.263 Angstrom, whereas T-N remains stable around 150 K. A magnetic phase diagram temperature-[r(A)] has been established, allowing five regions with different magnetic behaviours to be evidenced: paramagnetic insulating, ferromagnetic metallic, antiferromagnetic insulating, canted antiferromagnetic metallic, and weak ferromagnetic insulating. The extension of these regions is determined by the value of the applied magnetic field. (C) 1997 American Institute of Physics.