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<p>In this interesting study, we have prepared a compound with the nominal composition La<sub>0.7</sub>Ca<sub>0.2</sub>Sr<sub>0.1</sub>Mn<sub>1−<i>x</i></sub>Eu<sub><i>x</i></sub>O<sub>3</sub> using the sol–gel method, within the context of green chemistry. This paper is concerned with investigating the effect of Eu doping in the manganese site on the structural parameters, the magnetic and magnetocaloric effect properties, and the critical phenomena. The structural refinement of the x-ray diffraction (XRD) diagram confirmed the crystallization of the systems in an orthorhombic structure with <i>Pbnm</i> symmetry. Doping of Eu did not create any structural change, but it produced a change in the lattice parameter and the unit cell volume. The <i>M</i>(<i>T</i>) and <i>M</i>(<i>T</i>, <i>μ</i><sub>0</sub><i>H</i>) indicated that both compounds underwent a ferromagnetic-to-paramagnetic phase transition around the transition temperature (<i>T</i><sub>C</sub>. The inflection point was calculated by the derivative method, yielding values of 275&#xa0;K and 257&#xa0;K for <i>x</i> = 0 and <i>x</i> = 0.04, respectively. Investigation of the magnetocaloric effect revealed that the samples underwent an order-to-disorder magnetic transition. The maximum magnetic entropy change was 4.31 ± 0.01&#xa0;J/Kg&#xa0;K and 5.51 ± 0.02&#xa0;J/Kg&#xa0;K for <i>x</i> = 0 and <i>x</i> = 0.04, respectively. This increase in the magnetic entropy change, −Δ<i>S</i><sub>max</sub>, with Eu doping is explained by the distortion of the MnO<sub>6</sub> octahedral that favors the increase in spin–lattice coupling, which in turn increases the change in magnetic entropy. The universal master curve study showed that the compounds exhibited a second-order magnetic transition, which was confirmed through the Banerjee criteria. The study of the critical phenomena showed a sudden decline in the universal model from the mean field model to the tricritical mean field model with Eu doping. The exponent <i>β</i> decreased from 0.435 ± 0.01 to 0.244 ± 0.005, which confirms the important magnetic disorder of the compound at this level of doping.</p>

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Sudden Decline of the Critical Universal Model for the Nominal Compositions La0.7Ca0.2Sr0.1Mn1−xEuxO3 (x = 0 and 0.04) Synthesized by Sol–Gel Technique

  • 期刊论文

  • 发表日期：

    2025年2月14日

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  • M. R. Laouyenne,
  • Mohamed Baazaoui,
  • Fatma Aouaini,
  • Beriham Basha,
  • Kholoud Saad Al-mugren

摘要

In this interesting study, we have prepared a compound with the nominal composition La0.7Ca0.2Sr0.1Mn1−xEuxO3 using the sol–gel method, within the context of green chemistry. This paper is concerned with investigating the effect of Eu doping in the manganese site on the structural parameters, the magnetic and magnetocaloric effect properties, and the critical phenomena. The structural refinement of the x-ray diffraction (XRD) diagram confirmed the crystallization of the systems in an orthorhombic structure with Pbnm symmetry. Doping of Eu did not create any structural change, but it produced a change in the lattice parameter and the unit cell volume. The M(T) and M(T, μ0H) indicated that both compounds underwent a ferromagnetic-to-paramagnetic phase transition around the transition temperature (TC. The inflection point was calculated by the derivative method, yielding values of 275 K and 257 K for x = 0 and x = 0.04, respectively. Investigation of the magnetocaloric effect revealed that the samples underwent an order-to-disorder magnetic transition. The maximum magnetic entropy change was 4.31 ± 0.01 J/Kg K and 5.51 ± 0.02 J/Kg K for x = 0 and x = 0.04, respectively. This increase in the magnetic entropy change, −ΔSmax, with Eu doping is explained by the distortion of the MnO6 octahedral that favors the increase in spin–lattice coupling, which in turn increases the change in magnetic entropy. The universal master curve study showed that the compounds exhibited a second-order magnetic transition, which was confirmed through the Banerjee criteria. The study of the critical phenomena showed a sudden decline in the universal model from the mean field model to the tricritical mean field model with Eu doping. The exponent β decreased from 0.435 ± 0.01 to 0.244 ± 0.005, which confirms the important magnetic disorder of the compound at this level of doping.