Abstract
We present a detailed study on the physical properties of La0.6Ba0.2Sr0.2Mn1−xNixO3 samples (x = 0.00, 0.05 and 0.1). The ceramics were fabricated using the sol–gel route. Structural refinement, employing the Rietveld method, disclosed a rhombohedral R3̄c phase. The magnetization vs. temperature plots show a paramagnetic–ferromagnetic (PM–FM) transition phase at the TC (Curie temperature), which decreases from 354 K to 301 K. From the Arrott diagrams M2vs. μ0H/M, we can conclude the phase transition is of the second order. Based on measurements of the isothermal magnetization around TC, the magnetocaloric effects (MCEs) have been calculated. The entropy maximum change (−ΔSM) values are 7.40 J kg−1 K−1, 5.6 J kg−1 K−1 and 4.48 J kg−1 K−1, whereas the relative cooling power (RCP) values are 232 J kg−1, 230 J kg−1 and 156 J kg−1 for x = 0.00, 0.05 and 0.10, respectively, under an external field (μ0H) of 5 T. Through these results, the La0.6Ba0.2Sr0.2Mn1−xNixO3 (0 ≤ x ≤ 0.1) samples can be suggested for use in magnetic refrigeration technology above room temperature. The electrical resistivity (ρ) vs. temperature plots exhibit a transition from metallic behavior to semiconductor behavior in the vicinity of TM–SC. The adiabatic small polaron hopping (ASPH) model is applied in the PM-semiconducting part (T > TMS). Throughout the temperature range, ρ is adjusted by the percolation model. This model is based on the phase segregation of FM-metal clusters and PM-insulating regions.
Highlights
Magnetic refrigeration (MR) technology based on the magnetocaloric effect (MCE) is advancing to become a suitable technology, compared to conventional gas refrigeration,[1,2,3] due to a number of advantages.[4]
To better understand the performance of the MCE of our compounds, the values of (ÀDSm Max) and relative cooling power (RCP) are compared to other manganites, as given in Table 4.58–62 It can be noted that our samples, especially for x 1⁄4 0.1, have a suitable TC value, close to room temperature (RT), and a relatively large magnetic entropy change to include other materials
We have investigated the physical properties of polycrystalline La0.6Ba0.2Sr0.2Mn1ÀxNixO3 samples
Summary
Magnetic refrigeration (MR) technology based on the magnetocaloric effect (MCE) is advancing to become a suitable technology, compared to conventional gas refrigeration,[1,2,3] due to a number of advantages.[4]. The pure stoichiometric lanthanum manganite LaMnO3 is antiferromagnetic, insulating at 150 K, and the substitution of the rare earth element by a lower valence ion causes the oxidation of Mn3+ into Mn4+ to ensure electroneutrality in the material. It is followed by the appearance of macroscopic magnetization, i.e. a ferromagnetic coupling between the Mn3+ ions (t2g3e1g) and the Mn4+ ion (t2g3e0g). Based on the information given in this article, we have carefully discussed the physical properties in La0.6Ba0.2Sr0.2Mn1ÀxNixO3 (0 # x # 0.1) compounds
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