Abstract
The work presents the magnetocaloric effect and critical behavior of monoclinic polycrystalline Pr0.7CaxSr0.3-xMnO3 prepared by solid state reaction. The ferromagnetic-paramagnetic phase transition temperature decreases from 267, 202, 138 to 126 K with increasing doping concentration from x=0 to 0.3. The maximum values of entropy change appear near the transition phase points and were found to be 6.4, 7.2, 3.9 and 4.0 J.kg-1.K-1 with 5 Tesla of field change for x=0-0.3, respectively. However, the shift to the higher temperature side with the increasing field change was observed clearly in sample x=0.1. Besides, the considering magnetic phase transition of samples based on Banerjee’s criterion showed a first-order phase transition in Pr0.7Ca0.1Sr0.2MnO3 (x=0.1) while samples with x=0, x=0.2 and 0.3 exhibited a second-order phase transition.
Highlights
The magnetic refrigeration (MR) based magnetocaloric effect (MCE) is an exciting research direction recently
In alkali-doped manganites Ln1-xAxMnO3, it is shown that the magnetic properties as magnetocaloric effect or magnetoresistance are strongest with x ≈ 0.3 corresponding to concentration ratio Mn3+/Mn4+ of 7/3.2–4 Phan and co-workers reported a high MCE with adiabatic temperature change of 5.65 K at room temperature for ∆μoH=5 T in single crystal Pr0.63Sr0.37MnO3.5 Magnetocaloric property of Pr0.7Sr0.3MnO3 nanocrystalline though is slightly lower than that in single crystal and quite impressive with magnetic entropy change ∆S=6.3 J.kg-1.K-1 near 235 K for same field change of 5 T
The presence of FM clusters may lead to the increase of inhomogeneity of FM states and affect MCE property and critical behaviors of compounds
Summary
The magnetic refrigeration (MR) based magnetocaloric effect (MCE) is an exciting research direction recently. The nature of magnetotransport in this compound belonged to a second-order phase transition obeying well Landau’s theory.[6] As known in manganite based magnetocaloric materials, MCE in vicinity of T C is related strictly to the magnetic phase transition.[7,8,9,10] This is supposed to be derived from the magnetic orders in compound which is defined by the ratio Mn3+/Mn4+ as well as spin configurations of these ions. A long-range ferromagnetic ordering which stipulates a SOPT may be declined or even broken and a second-to-first-order magnetic phase transformation can happen.[4,9] An inhomogeneity of FM states can be cause for different magnetic behaviors as mean-field model, 3D-Ising, 3D-Heisenberg or tritical mean-field types.[11,12,13]
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