Structural insights into the rare-earth modified La1.4-xSmxSr1.6Mn2O7 layered perovskites and probing their complex magnetic and magnetocaloric properties

Abstract

In this work, structural characteristics upon rare-earth modification into the Ruddlesden-Popper (R-P) layered compounds La1.4-xSmxSr1.6Mn2O7 (0.00 ≤ x ≤ 0.20) were deeply investigated. The compounds were prepared through conventional ceramic-sintering method. X-ray diffraction (XRD) and Raman spectra collectively disclosed a reduction in the unit cell dimensionality and emergence of structural distortions upon Sm-modification which facilitated the separation of structural phases. Unlike the cubic manganites these distortions impart a chemical pressure mainly along c-axis of the tetragonal cell and favored a weak interbilayer exchange interaction native to layered lattice. The magnetization vs temperature (M-T) curves revealed multiple transitions that were chiefly attributed to such anisotropic exchange coupling and to a separate perovskite phase. The appearance of magnetic clusters was further confirmed in magnetization isotherms (M − H curves) and Arrott plots. The highest change in magnetic entropy (ΔSM) of 2.28 Jkg−1K−1 at 2.5 T field was obtained for pristine compound, the value slightly decreased to 1.78 Jkg−1K−1 for x = 0.05, and then increased up to 1.90 Jkg−1K−1 for x = 0.1 composition. Whereas the relative cooling power (RCP) abruptly enhanced to 100 J/kg, 110 J/kg and 92 J/kg for x = 0.05, 0.10 and x = 0.15 samples, respectively as compared to original value of 84 J/kg. It signifies an excellent magnetocaloric performance for x = 0.05 and 0.1 compositions over various categories of material systems and asserting the technological competence of these compounds for low temperature refrigeration applications.