Abstract:
The structural, magnetic and magnetocaloric properties of three series of compositions La0.55CaxSr0.45-xMnO3, Pr0.55CaxSr0.45-xMnO3 and Sm0.55CaxSr0.45-xMnO3 (x = 0.00, 0.05, 0.1, 0.2 and 0.25) synthesized by solid state reaction technique have been investigated. Room temperature XRD measurements reveal rhombohedral structure for all the compounds of La0.55CaxSr0.45-xMnO3 and orthorhombic structure for all the compounds of Pr0.55CaxSr0.45-xMnO3 and Sm0.55CaxSr0.45- xMnO3. With increase in Ca content, lattice parameters and Mn-O-Mn bond angles are found to decrease. These structural changes control ferromagnetism in the materials via double-exchange mechanism. The calculated values of chemical composition using the EDX data were in well agreement with the nominal one. Arrott plots confirm that all the samples undergo second-order ferromagnetic (FM) to paramagnetic (PM) phase transition for La0.55CaxSr0.45-xMnO3 and Pr0.55CaxSr0.45-xMnO3 series and first-order FM to PM phase transition for Sm0.55CaxSr0.45-xMnO3 series. Curie temperature (TC) decreases with increase in Ca content for all three series but saturation magnetization decreases with increase in Ca content in La0.55CaxSr0.45-xMnO3, and Sm0.55CaxSr0.45-xMnO3 while increases for Pr0.55CaxSr0.45-xMnO3. Critical exponent values calculated from modified Arrott plots, Kouvel–Fisher method and critical isotherm analysis disclose the presence of long range ferromagnetic interaction in Pr0.55CaxSr0.45-xMnO3 and La0.55CaxSr0.45-xMnO3 with x=0.00, 0.05, 0.1 and short-range ferromagnetic interactions in samples with x=0.2 and 0.25. The magnetocaloric effect was calculated in terms of entropy change (-ΔSM) and relative cooling power (RCP). The TC values of Pr0.55CaxSr0.45-xMnO3 series are found to decrease from 290 to 230 K while both maximum entropy change ((-ΔSM)max) and RCP increase with the increase of Ca content. For La0.55CaxSr0.45-xMnO3 series values of (-ΔSM)max and RCP are found to decrease with the increase in Ca content while increase in Ca content tunes the TC near room temperature. The TC values of the samples of series Sm0.55CaxSr0.45-xMnO3 are found to decrease from 116 to 75 K and both
(-ΔSM)max and RCP values also decrease with increase in Ca content. These properties make Pr0.55CaxSr0.45-xMnO3, La0.55CaxSr0.45-xMnO3 and Sm0.55CaxSr0.45-xMnO3 as potential materials for magnetic cooling technology at below room temperature, above room temperature and low temperature applications, respectively.
