Phase separation in (La_0.4Pr_0.6)_1-xCa_xMnO₃ (x = 3/8, 1/3) mixed phase manganites

Here, we present a study on structural and magneto-transport properties of in (La_0.4Pr_0.6)_1-xCa_xMnO₃ (x = 3/8 (LPCMO1), 1/3 (LPCM02)) mixed phase manganites. Owing to the close chemical composition, LPCMO1 and LPCM02 have very similar crystal structures and cell parameters. However, temperature dependent magneto transport and magnetization profiles show a significant variation, especially in ferromagnetic and metal-insulator transition temperatures. The FM and CO-AFM phase fractions below saturation magnetic field are found to be very different for both the samples. Single phase polycrystalline samples were prepared by the conventional solid state reaction method. The crystalline structure of these manganites has been determined using room temperature x-ray and neutron diffraction measurements, The phase purity of the samples was checked by analysing both XRD and ND patterns using the Rietveld method, where the refinement was carried out using the orthorhombic unit cell with Pnma space group. Mn-O1-Mn and MnO₂-Mn bond angles are found to be less than 180 ° for both the compounds, indicating the presence of an octahedral distortion in the structure. A quantitative measure of distortion can be given in terms of the Mn-O bond length by using the octahedral distortion parameter (d). We found d to be 5 x 10^-4 and 3.7 x10^-5 for LPCMO1 and LPCMO2 respectively. The variation in octahedral distortion can manifest in crystal field interactions and influence the magnetic ground state of these manganites. This is supported by magnetization and magneto-transport measurements. (author)