Field induced ferromagnetic phase transition and large magnetocaloric effect in Sm 0.55 Sr 0.45 MnO 3 phase separated manganites S.K. Giri a , Papri Dasgupta b , A. Poddar b , A.K. Nigam c , T.K. Nath a,⇑ a Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur, West Bengal 721 302, India b Experimental Condensed Matter Physics Division, Saha Institute of Nuclear Physics, West Bengal, India c Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India article info Article history: Received 14 June 2013 Received in revised form 10 August 2013 Accepted 13 August 2013 Available online 27 August 2013 Keywords: Magnetocaloric effect First order magnetic phase transition Relative cooling power Manganites abstract 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 (|DS 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 temper- ature (T C )–172 K after the correction for hysteretic losses caused by the first order magnetic phase tran- sition. 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 max- imum 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 man- ganites. 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 cool- ing 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 cri- teria 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 transi- tion 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. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The magnetocaloric effect (MCE) is generally characterized by the isothermal change of the magnetic entropy and the adiabatic change of temperature by the application of external magnetic field [1]. Magnetic refrigeration based on MCE has attracted much research interest due to its potential advantage of environmental friendliness over gas refrigeration. Magnetic refrigeration makes use of solid refrigerants (ferromagnetic) instead of environmen- tally harmful gases and is considered to be more efficient than the conventional vapor compression based refrigeration. The work- ing principle of magnetic refrigeration is the MCE which refers to an adiabatic change in the temperature and isothermal change of magnetic entropy when the sample is subjected to a changing magnetic field. The change in magnetic entropy i.e. DS M ¼ R H 0 ð@M=@T Þ H dH is expected to maximum at the paramag- netic to ferromagnetic transition temperature (T C ). Majority of materials show second order paramagnetic to ferromagnetic phase transition. However, for a few materials like Gd 5 Si 2 Ge 2 , [2] and Ni 2- MnGa, [3] magnetization changes abruptly around T C i.e. show first-order magnetic phase transition, leading to a giant MCE. As the magnetic entropy change is expected to be greatly enhanced at the first order magnetic phase transition, it is needed to synthe- size new compound of strongly coupled structural and magnetic order parameters [4]. Mostly, the rare earth material and its alloys show large mag- netocaloric effect due to its large magnetic moment [5]. However, 0925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2013.08.093 ⇑ Corresponding author. Tel.: +91 3222 283862; fax: +91 3222 255303. E-mail address: tnath@phy.iitkgp.ernet.in (T.K. Nath). Journal of Alloys and Compounds 582 (2014) 609–616 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom