Field-induced entropy change in the manganite with significant short-range magnetic order

Effects of short-range magnetic order on magnetic entropy change have been studied for the manganese oxide Eu0.55Sr0.45MnO3. Superparamagnetic clusters composed of seven to ten Mn ions, depending on applied field, have been derived in the paramagnetic state of the compound based on the analysis of dc susceptibility. The presence of short-range magnetic order greatly depresses the magnetic entropy of the paramagnetic phase; thus the entropy changes at the field-induced paramagnetic to ferromagnetic phase transition. The maximum entropy change detected is only ∼7J∕kgK for a field change of 0–5T, about one-fifth of the theoretical expectation. The experimental results can be well elucidated within the mean field theory. It is suggested that a way of destroying the short-range order would enhance the magnetic entropy change greatly.