Chebaane M, Bellouz R, Oumezzine Ma, Hlil E K, Fouzri A
Laboratory of Physical Chemistry of Materials, Faculty of Sciences of Monastir, University of Monastir 5019 Monastir Tunisia
Institut Néel, CNRS-Université J. Fourier B.P. 166 38042 Grenoble France.
RSC Adv. 2018 Feb 13;8(13):7186-7195. doi: 10.1039/c7ra13244a. eCollection 2018 Feb 9.
Bulk nanocrystalline samples of LaCeSrMn Cu O (0 ≤ ≤ 0.15) manganites are prepared by the sol-gel based Pechini method. The effect of the substitution for Mn with Cu upon the structural and magnetic properties has been investigated by means of X-ray diffraction (XRD), Raman spectroscopy and dc magnetization measurements. The structural parameters obtained using Rietveld refinement of XRD data showed perovskite structures with rhombohedral (3̄) symmetry without any detectable impurity phase. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing copper concentration. The analysis of the crystallographic data suggested a strong correlation between structure and magnetism, for instance a relationship between a distortion of the MnO octahedron and the reduction in the Curie temperature, . A paramagnetic to ferromagnetic phase transition at is observed. The experimental results confirm that Mn-site substitution with Cu destroys the Mn-O-Mn bridges and weakens the double exchange (DE) interaction between Mn and Mn ions, which shows an obvious suppression of the FM interaction in the LaCeSrMn Cu O matrix. The maximum magnetic entropy change -Δ is found to decrease with increasing Cu content from 4.43 J kg K for = 0 to 3.03 J kg K for = 0.15 upon a 5 T applied field change.
采用基于溶胶 - 凝胶的佩琴尼法制备了LaCeSrMn₁₋ₓCuₓO₃（0 ≤ x ≤ 0.15）锰氧化物的块状纳米晶样品。通过X射线衍射（XRD）、拉曼光谱和直流磁化测量研究了用Cu替代Mn对结构和磁性的影响。利用XRD数据的Rietveld精修获得的结构参数表明，样品具有菱面体（R3̄）对称的钙钛矿结构，且未检测到任何杂质相。室温下的拉曼光谱显示，随着铜浓度的增加，声子模式逐渐变化。晶体学数据分析表明结构与磁性之间存在很强的相关性，例如MnO八面体的畸变与居里温度TC的降低之间的关系。观察到在TC处发生顺磁到铁磁的相变。实验结果证实，用Cu替代Mn位点会破坏Mn - O - Mn桥，并削弱Mn离子与Mn离子之间的双交换（DE）相互作用，这表明LaCeSrMn₁₋ₓCuₓO₃基体中的铁磁相互作用受到明显抑制。在5 T的外磁场变化下，发现最大磁熵变 -ΔSm随着Cu含量的增加而降低，从x = 0时的4.43 J kg⁻¹K⁻¹降至x = 0.15时的3.03 J kg⁻¹K⁻¹。
