Field induced ferromagnetic phase transition and large magnetocaloric effect in Sm0.55Sr0.45MnO3 phase separated manganites

Abstract

(a) Magnetic field and particle size dependent T C of nanometric (black and red dot) and bulk (blue and wine dot) measured upon cooling (full dots) and warming (open dots). (b) Temperature dependence magnetic entropy change Δ S at different magnetic field calculated from the magnetization data of S1250 bulk sample. • Large magnetocaloric effect is reported based on the first order phase transition. • The value of |Δ S M | reaches a maximum value of 8.48 J/kg K at 60 kOe field. • A large relative cooling power (∼574 J/kg) around T C –172 K is reported. • The adiabatic temperature change is found to be 2.38 K for magnetic field of 10 kOe. • Noticeable |Δ S M | at low field makes the system useful for magnetic refrigeration. This paper reports about the magnetocaloric effect and relative cooling power based on the first order magnetic phase transition in Sm 0.55 Sr 0.45 MnO 3 polycrystalline phase separated manganites. Upon 60 kOe applied magnetic field, the magnetic entropy change (|Δ S M |) of bulk sample reaches a maximum value of 8.48 J/kg-K with a large relative cooling power (RCP) value of 574 J/kg around its Curie temperature ( T C )–172 K after the correction for hysteretic losses caused by the first order magnetic phase transition. The corresponding adiabatic temperature change is 2.38 K for magnetic field of 10 kOe. The magnetic field induced change of entropy and specific heat vary with temperature and have their maximum around the first order magnetic phase transition. We also report the magnetic field dependence of the order of the ferromagnetic (FM) to paramagnetic (PM) phase transition in bulk and nanometric manganites. It has been shown that bulk to nanometric samples exhibit first order FM → PM phase transition under low magnetic field accompanied by magnetization with thermal hysteresis in the field cooled cooling and warming cycle. However, the samples exhibit a second order magnetic phase transition above a critical field H CR . All the signatures of the first-order magnetic phase transition in bulk and nanometric sample disappear above the critical field H CR . The magnetocaloric effect is thus modified by the field induced order of magnetic phase transition. The field induced paramagnetic to ferromagnetic transition is confirmed to be first order in nature from dc magnetization measurements and Arrott plots using a criteria given by Banerjee. The magnetic phase transition is also accompanied by a large change in resistivity with thermal hysteresis. The observed value of magnetic entropy change in bulk sample is much higher than the value generally observed in other perovskite manganites of comparable T C . This large change mainly originates from a sharp magnetization jump, associated with a first-order metamagnetic transition and coalescence of ferromagnetic clusters in the paramagnetic state. Such noticeable magnetic entropy change at low magnetic field makes this material useful for the application of active magnetic refrigerant (AMR) materials.