Arun B, Akshay V R, Vasundhara M
Materials Science and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology Trivandrum India
Academy of Scientific and Innovative Research (AcSIR), CSIR-Human Resource Development Centre Ghaziabad Uttar Pradesh India.
RSC Adv. 2019 Jul 30;9(41):23598-23606. doi: 10.1039/c9ra04973h. eCollection 2019 Jul 29.
The effect of Sr-site deficiency on the structural, magnetic and magnetic entropy change of LaSrMnO ( = 0.18 and 0.27) compounds was investigated. The compounds were prepared by the conventional solid-state route and powder X-ray diffraction technique along with Rietveld refinement was carried out to confirm the structure and phase purity. Lattice parameters and unit cell volumes are found to increase with the increase in Sr-deficiency due to the electrostatic repulsion from the neighbouring oxygen ions. A mixed valence state of Mn/Mn/Mn was confirmed using the X-ray photoelectron spectroscopy technique and it was observed that the change of state from Mn + Mn pairs to Mn + Mn pairs is different for both the studied compounds. A second order ferromagnetic-paramagnetic transition with an enhancement in magnetization in comparison to the pristine compound (LaSrMnO) was observed due to multiple double exchange interactions. The LaSr□MnO compound exhibits a magnetic entropy change (Δ ) of 4.61 J kg K at 310 K, and the LaSr□MnO compound exhibits a Δ of 4.11 J kg K at 276 K under a field of 50 kOe. In our previous work, we reported a large value of Δ but at higher temperatures, around 350 K. However, in the present case, we have achieved a near room temperature (310 K) MCE with a significant Δ value (4.61 J kg K) which is larger than that reported for numerous perovskite manganites. Thus, the studied material could be a potential candidate for room temperature magnetic refrigeration applications.
研究了Sr位缺陷对LaSrMnO（= 0.18和0.27）化合物的结构、磁性和磁熵变的影响。采用传统的固态路线制备了这些化合物，并利用粉末X射线衍射技术以及Rietveld精修来确认结构和相纯度。由于相邻氧离子的静电排斥作用，发现晶格参数和单胞体积随Sr缺陷的增加而增大。使用X射线光电子能谱技术确认了Mn/Mn/Mn的混合价态，并且观察到对于这两种研究的化合物，从Mn + Mn对到Mn + Mn对的状态变化是不同的。由于多重双交换相互作用，观察到与原始化合物（LaSrMnO）相比，具有增强磁化强度的二级铁磁 - 顺磁转变。在50 kOe的磁场下，LaSr□MnO化合物在310 K时表现出4.61 J kg K的磁熵变（Δ ），LaSr□MnO化合物在276 K时表现出4.11 J kg K的Δ 。在我们之前的工作中，我们报道了较大的Δ 值，但在较高温度下，约为350 K。然而，在目前的情况下，我们在接近室温（310 K）时实现了具有显著Δ 值（4.61 J kg K）的磁热效应，该值大于许多钙钛矿锰氧化物所报道的值。因此，所研究的材料可能是室温磁制冷应用的潜在候选材料。
