Cation size-temperature phase diagram of the manganites Ln0.5Sr0.5MnO3

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Abstract
We have studied the variation of the paramagnetic to ferromagnetic transition temperature TC and of the ferromagnetic to antiferromagnetic transition temperature TN as a function of the average size of the A site cations (Ln, Sr) in the manganite perovskites Ln0.5Sr0.5MnO3 (Ln=Gd, Sm, Y, Pr, La). For our investigation we used dc resistivity, magnetization, susceptibility and magnetoresistance measurements. Results show that the Curie temperature TC increases from 85 to 310 K when 〈rA〉 varies from 1.221 to 1.263 Å, whereas TN remains stable around 150 K. A magnetic phase diagram temperature-〈rA〉 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.