A new range of specific perovskite-type materials with structural, magnetic and magnetocaloric properties: La0.67Ca0.33-xSrxMn0.98Fe0.02O3 (0.15 ≤ x ≤ 0.3)
Graphical abstract
Introduction
Manganites of general formula Tr1- xDxMnO3 (in which Tr is a rare earth ion and D is an alkaline earth or alkaline ion) are very attractive due to their potential technological applications such as magnetocaloric cooling devices and magneto-electronic technology [1]. The magnetocaloric effect (MCE) is defined as a typical property of magnetic materials consisting of an adiabatic variation of temperature due to variations of external magnetic field [2,3]. The nature of magnetic properties of manganites depends principally on the existence of a mixed-valence state Mn3+/Mn4+. Ferromagnetic (FM) and antiferromagnetic (AFM) interactions, which results from Mn3+ - Mn4+, Mn3+-Mn3+, and Mn4+-Mn4+ ion pairs, respectively, are driven by the latter. An electron transfer that occurs between neighboring ions Mn3+ and Mn4+ through the oxygen anion O2− explains the double exchange (DE) model [4]. Therefore, these electrons' spins are parallel, causing a ferromagnetic metal transition. Numerous investigations as reported in the literature have shown significant MCE values for selected manganites near room temperature [5,6].
Among these manganites, LaMnO3 is defined as an antiferromagnetic insulator (AFI) characterized by a super-exchange coupling (SE) between Mn3+ ions [7]. Substituting the A-site or the B-site can easily influence the properties of such manganite, as reported in the literature [8,9]. Ferromagnetic metallic properties of new manganites found origin from a partial substitution of La3+ by divalent ions such as Ca2+, Sr2+, Ba2+, etc, as explained by the Zener theory (double exchange). In comparison, La0.7Ca0.3MnO3 exhibits a higher magnetocaloric effect (MCE) as compared to La0.7Sr0.3MnO3, but with a reduced Curie temperature below room temperature. Doping Ca manganites with low amounts of Sr raises the Curie temperature towards ambient temperature, resulting in a significant advance toward magnetic refrigeration based applications, but at the cost of a smaller MCE [10].Whereas (x = 0.2, 0.33) has a larger magnetic entropy change compared to gadolinium [11], while its Curie temperature (TC) is 251 K, lower than 294 K for Gd [12], which makes it a promising material for magnetic refrigeration at room temperature. Furthermore, has significant magnetocaloric properties [13] with TC = 346 K for x = 0.25 [14]. Significantly, increasing Sr in the compound decreases Tc closer to room temperature [15]. Substitution of A site by Sr and Ca ions affects Tc, due to the difference between the ionic radii of the two ions [16].
In the present study, we investigated the effect of A-site substitution on the.structural, magnetic, and magnetocaloric.properties of.La0.67Ca0.33-xSrxMn0.98Fe0.02O3 for (x = 0.15; 0.2 and.0.3) manganites.
Section snippets
Materials and methods
Sr-doped manganites.La0.67Ca0.33-xSrxMn0.98Fe0.02O3 with (x = 0.15; 0.2.and 0.3) have.been synthesized in.air via the sol-gel method using C6H9LaO6, H2O, C4H6CaO4,H2O, N2O6Sr, C4H6MnO4, 4H2O and Fe2O3 precursors. The Stoichiometric amounts of precursors were diluted in distilled water to obtain a mixed solution. Afterwards, a hot plate on which the solution was heated with stirring equal to 90 °C. After complete dissolution of the precursors, the citric acid (used as complexation agent for the
X-ray diffraction analysis
Fig. 1(a) shows the X-ray powder diffraction patterns of polycrystalline samples La0.67Ca0.33-xSrxMn0.98Fe0.02O3for (x = 0.15; 0.2 and.0.3). From the obtained results, all the compounds have a single phase without any detectable secondary phase. The data have been refined using the standard Rietveld method using Fullprof software [[17], [18], [19]]. At room temperature, we have indexed the XRD data corresponding to x = 0.15 within a rhombohedral structure with Pnma spatial group. Inside the
Conclusion
In summary, the structure, magnetic and magnetocaloric properties of La0.67Ca0.33-xSrxMn0.98Fe0.02O3 manganites have been investigated for (x = 0.15; 0.2 and 0.3). The crystal structure of all samples was obtained from Rietveld's refinements of the X-ray diffraction spectra. The x = 0.15 compound exhibits an orthorhombic structure with the Pnma space group, whereas the structure of x = 0.2 and x = 0.3 compounds is rhombohedral with the Rc space group. All compound have soft ferromagnetic
Author statement
K. Laajimi synthesized the samples and performed with F. Ayadi, M. Kchaw, and I. Fourati the structural and magnetic characterizations, and data analysis. M. Khlifi, M. H. Gazzah., J. Dhahri and J. Juraszek discussed the results. K. Laajimi wrote the manuscript which was reviewed by all the authors.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
K.J is grateful for the financial support from the Tunisian Ministry of Higher Education and Scientific Research for a travelling scholarship. Region of Normandy and the European Regional Development Fund of Normandy (ERDF) in the frame of the MAGMA project supported this work.
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