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 tra nsition 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. Re sults show that the Curie temperature T-C increases from 85 to 310 K w hen [r(A)] varies from 1.221 to 1.263 Angstrom, whereas T-N remains st able around 150 K. A magnetic phase diagram temperature-[r(A)] has bee n established, allowing five regions with different magnetic behaviour s to be evidenced: paramagnetic insulating, ferromagnetic metallic, an tiferromagnetic insulating, canted antiferromagnetic metallic, and wea k ferromagnetic insulating. The extension of these regions is determin ed by the value of the applied magnetic field. (C) 1997 American Insti tute of Physics.