A comparison study of the entropy changes in materials with and without short-rangemagnetic order

Abstract

The effects of short-range magnetic order (SRMO) on magnetic entropy changes have been studied for thecompounds Sm0.55Sr0.45MnO3, Eu0.55Sr0.45MnO3 and the rare-earth metal Gd. Ferromagnetic clusters composed of∼8 Mn ions are found to be formed in the paramagnetic phase of the manganites based on theanalysis of susceptibility. As a result, the entropy change for a field variation of 0–5 T is∼6 J kg−1 K−1 forSm0.55Sr0.45MnO3 and∼7 J kg−1 K−1 forEu0.55Sr0.45MnO3, wellbelow the values expected without considering the effect of SRMO. (The maximum entropy change willbe ∼56 J kg−1 K−1 for both compounds.) Assuming the presence of sizable magnetic clusters, the field-inducedentropy change, not only its peak value but also its temperature dependence, can bewell reproduced by the mean field theory. The average cluster size is found to bem≈8, in agreement with the result obtained from a Curie–Weiss analysis ofthe susceptibility. The presence of SRMO reduces the entropy change by∼80%. In contrast, the mean field theory gives a good description of the entropy change in Gd,for which no significant SRMO is observed. The present work reveals the important role ofSRMO in modifying the magnetocaloric properties of the magnetic materials.