Observation of enhanced magnetic entropy change near room temperature in Sr-site deficient La0.67Sr0.33MnO3 manganite

The effect of Sr-site deficiency on the structural, magnetic and magnetic entropy change of La0.67Sr0.33-yMnO3-delta (y = 0.18 and 0.27) compounds was investigated. The compounds were prepared by the conventional solid-state route and powder X-ray diffraction technique along with Rietveld refinement was carried out to confirm the structure and phase purity. Lattice parameters and unit cell volumes are found to increase with the increase in Sr-deficiency due to the electrostatic repulsion from the neighbouring oxygen ions. A mixed valence state of Mn2+/Mn3+/Mn4+ was confirmed using the X-ray photoelectron spectroscopy technique and it was observed that the change of state from Mn3+ + Mn3+ pairs to Mn2+ + Mn4+ pairs is different for both the studied compounds. A second order ferromagnetic-paramagnetic transition with an enhancement in magnetization in comparison to the pristine compound (La0.67Sr0.33MnO3) was observed due to multiple double exchange interactions. The La0.67Sr0.150.18MnO3-delta compound exhibits a magnetic entropy change (Delta S-M) of 4.61 J kg(-1) K-1 at 310 K, and the La0.67Sr0.060.27MnO3-delta compound exhibits a Delta S-M of 4.11 J kg(-1) K-1 at 276 K under a field of 50 kOe. In our previous work, we reported a large value of Delta S-M but at higher temperatures, around 350 K. However, in the present case, we have achieved a near room temperature (310 K) MCE with a significant Delta S-M value (4.61 J kg(-1) K-1) which is larger than that reported for numerous perovskite manganites. Thus, the studied material could be a potential candidate for room temperature magnetic refrigeration applications.