Materials Science and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Trivandrum, India.
Dalton Trans. 2018 Nov 21;47(43):15512-15522. doi: 10.1039/c8dt03538e. Epub 2018 Oct 19.
In this paper, we have studied the effect on the structural, magnetic and magnetocaloric properties of La and Sr-deficiencies in the LaSrMnO compound. Rietveld refinement of the X-ray powder diffraction patterns confirms that all of the compounds have crystallized into a rhombohedral crystal symmetry with an R3[combining macron]c space group. X-ray photoelectron spectroscopy measurements revealed that the parent compound has a mixed valance of Mn/Mn, whereas Mn/Mn/Mn mixed valency is found in the case of both La and Sr-deficient compounds. The LaSrMnO compound shows a magnetic transition temperature of 365 K, while the La and Sr-deficient compounds exhibit transition temperatures of 367 K and 355 K, respectively. Among the studied compounds, the Sr-deficient compound shows the highest magnetic entropy change (ΔS) of 5.08 J kg K at 352 K for a 50 kOe field with a relative cooling power (RCP) of 142 J kg and an adiabatic temperature change of 3.48 K, while the parent and La-deficient compounds exhibit a -ΔS of 4.78 J kg K at 364 K and of 4.12 J kg K at 364 K, respectively. The temperature dependence of the electrical resistivity with and without applied magnetic fields reveals that the La-deficient compound has one order and the Sr-deficient compound has two orders of suppression in the electrical resistivity. Thus, the Sr-deficient compound shows promising behaviour for reduction of the magnetic transition temperature towards room temperature, along with an increase in the ΔS values, and enhancement in the electrical conductivity. Therefore, it could be possible to tune the transition temperature towards room temperature without compromising the magnetic entropy change in order to develop materials for magnetic refrigeration applications.
在本文中，我们研究了 La 和 Sr 缺乏对 LaSrMnO 化合物结构、磁性和磁热性质的影响。X 射线粉末衍射图谱的 Rietveld 精修证实，所有化合物均已结晶为具有 R3[combining macron]c 空间群的三方晶系。X 射线光电子能谱测量表明，母体化合物具有 Mn/Mn 的混合价态，而在 La 和 Sr 缺乏的化合物中发现了 Mn/Mn/Mn 混合价态。LaSrMnO 化合物表现出 365 K 的磁转变温度，而 La 和 Sr 缺乏的化合物分别表现出 367 K 和 355 K 的转变温度。在所研究的化合物中，Sr 缺乏的化合物在 50 kOe 磁场下于 352 K 时表现出最高的磁熵变化 (ΔS) 为 5.08 J kg K，相对冷却功率 (RCP) 为 142 J kg，绝热温度变化为 3.48 K，而母体和 La 缺乏的化合物在 364 K 时表现出 -ΔS 为 4.78 J kg K，在 364 K 时表现出 -ΔS 为 4.12 J kg K。施加和不施加磁场时电阻率的温度依赖性表明，La 缺乏的化合物的电阻率降低了一个数量级，Sr 缺乏的化合物的电阻率降低了两个数量级。因此，Sr 缺乏的化合物表现出有希望的行为，即降低磁转变温度接近室温，同时增加 ΔS 值，并提高电导率。因此，有可能在不影响磁熵变化的情况下将转变温度调至室温，以开发用于磁制冷应用的材料。
