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19. Tuning the magnetocaloric properties of lanthanum–strontium manganite by rare-earth Nd3+ doping.

Author

Bolarín-Miró, A. M., Taboada-Moreno, C. A., Cortés-Escobedo, C. A., and Sánchez-De Jesús, F.

Subjects
CURIE temperature, MAGNETOCALORIC effects, RIETVELD refinement, MAGNETIZATION measurement, LATTICE constants
Abstract

This study investigated the effect of neodymium (Nd) on the crystal structure and magnetocaloric properties of lanthanum–strontium manganites (La0.7−xNdxSr0.3MnO3, 0 ≤ x ≤ 0.4), synthesized by assisted high-energy ball milling. Rietveld analysis from X-ray diffraction disclosed that Nd3+ did not promote crystallographic phase transitions. The rhombohedral crystal structure remained in the R-3c space group for all the compositions, with slight changes in lattice parameters. The defect model allowed the quantification of the Mn4+ occupancy, which is in the range from 0.20 to 0.26 mol, for 0.1 and 0.4 mol of Nd3+, respectively. The presence of Mn4+ promoted further ferromagnetic interactions, increasing systematically the saturation magnetization, from 65 A·m2·kg−1 to 73 A·m2·kg−1, and a diminution in the Curie temperature from 364 to 255 K, for 0 and 0.4 mol of Nd3+, respectively, obtained by temperature-dependent magnetization measurements. The doped manganite with 0.35 mol of Nd3+ showed a maximum of entropy change of 3.73 Jkg−1 K−1 at 1.8 T near room temperature, with a relative cooling power of 82 Jkg−1 and temperature-averaged entropy change, TEC(3) and TEC(10), of 3.53 and 3.06 Jkg−1 K−1, respectively. It is demonstrated that the presence of Nd3+ modulates the Curie temperature near room temperature and enhances the magnetocaloric properties at low magnetic fields, making these manganites a promising material for magnetocaloric applications. [ABSTRACT FROM AUTHOR]

Published
2024
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30. Induction of ferromagnetism in multiferroic LaFeO3 by doping with Ni2+.

Author

Téllez-Tovar, X. J., Aguirre-Espinosa, J. C., Sánchez-De Jesús, F., Cortés-Escobedo, C. A., and Bolarín-Miró, A. M.

Abstract

In this research, LaFeO3 doped with different concentrations of Ni2+ at Fe sites, ranging from 0.1 to 0.5 with a Δx of 0.1, was studied. The synthesis process involved high-energy milling followed by heat treatment at a low temperature, 1073 K, to induce ferromagnetic order (FM). Moreover, the effects of cation doping on the crystal structure and multiferroic properties were determined. X-ray diffraction analysis and Rietveld refinement confirmed that doped lanthanum ferrite with an orthorhombic structure (Pnma) was obtained for all the studied dopant levels. The magnetic hysteresis loops change from antiferromagnetic (AFM) to weakly ferromagnetic at room temperature when Ni2+ is introduced into the LaFeO3 crystal structure, which is attributed to spin canting due to the difference in ionic radius between the Fe3+ and Ni2+ cations and to the frustration of the magnetic cycloid due to the existence of uncompensated ions. Regarding the dielectric properties, the doped ferrites show semiconductor behavior with high values of relative permittivity as the doping concentration increases. XPS spectra confirmed the existence of adsorbed oxygen associated with oxygen affinity as a mechanism of charge compensation due to vacancies and oxidation from Fe3+ to Fe4+. [ABSTRACT FROM AUTHOR]

Published
2024
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