Impact of synthesis routes on normal and inverse magnetocaloric effects and critical behaviour in the charge-ordered Pr0.5Sr0.5MnO3 manganite

Abstract

We investigated the effect of both synthesis routes on the physical properties of charge-ordered Pr0.5Sr0.5MnO3 (PSMO) manganites. The samples are prepared by the solid-state reaction (SSR) and the modified sol-gel (SG) method. X-ray diffraction (XRD), SEM and magnetic measurement are used to study the structural, morphological, magnetic, magnetocaloric effect and the critical behaviour of our manganites. XRD studies confirmed the single phase orthorhombic formation of PSMO. Both compounds undergo two successive magnetic phase transitions with the variation of temperature: a paramagnetic (PM)-to-ferromagnetic (FM) transition around $ T_{\rm C}=265$ and 243K followed by an FM-to-antiferromagnetic charge-ordered transition at $ T_{\rm CO}=85$ and 159K for the SG and SSR methods, respectively. Moreover, Banerjee's criteria, Landau analysis and universal curves of phase transitions are also studied to access the magnetic ordering of the PM-FM transition in the samples and confirmed the second-order character. Critical exponents associated with the ferromagnetic phase transition are analyzed and found to be inconsistent with any known universality class. Important magnetic entropy changes and the relative cooling power (RCP) were observed in the sample synthesized through the solid state method as compared to the sol-gel-synthesized sample. The PSMO compounds show both negative ( $ \Delta S_{\rm M}=-1.63813$ J/kgK for SSR and -1.1 for SG) as well as positive ( $ \Delta S_{\rm M}=+5.82$ J/kgK for SSR and +1.52 for SG) magnetocaloric effects under a 2T field at ferromagnetic and charge order transitions, respectively. This feature of successive inverse and normal MCEs in Pr0.5Sr0.5MnO3 are suggested to be applied in some magnetic refrigerators with special designs and functions.