Anwar M S, Ahmed Faheem, Koo Bon Heun
J Nanosci Nanotechnol. 2014 Nov;14(11):8745-9. doi: 10.1166/jnn.2014.9994.
We report the sol-gel synthesis and impact of reduced dimensionality on the magnetocaloric properties of La0.6Ca0.4MnO3 manganite. The synthesized powders were characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and magnetization measurements. The XRD results indicated that the La0.6Ca0.4MnO3 nanoparticles have single phase nature with orthorhombic structure. FE-SEM results suggested that the nanoparticles are agglomerated and crystallite size increases with the annealing temperature. Magnetization measurements show that the La0.6Ca0.4MnO3 nanoparticles exhibit transition temperature (T(c)) below room temperature. The transition temperature was found to increase with the increasing the crystallite size. Maximum in magnetic entropy change, (ΔS(M))(max) shows interesting behaviour and was found to vary with the particle size. At magnetic field of 1 T, the value of (ΔS(M))(max) - 0.13 J/kg K was observed at 213 K for the sample annealed at 600 degrees C. Also, the increment in the value of (ΔS(M))(max) was observed at higher annealing temperature. This study shows that the magnetic entropy of pervoskite manganite can be tuned by tuning the crystallite size of the manganites.
我们报道了La0.6Ca0.4MnO3锰氧化物的溶胶-凝胶合成及其维度降低对磁热性能的影响。通过X射线衍射（XRD）、场发射扫描电子显微镜（FE-SEM）和磁化测量对合成的粉末进行了表征。XRD结果表明，La0.6Ca0.4MnO3纳米颗粒具有单相性质，结构为正交晶系。FE-SEM结果表明，纳米颗粒发生了团聚，且微晶尺寸随退火温度的升高而增大。磁化测量表明，La0.6Ca0.4MnO3纳米颗粒的转变温度（T(c)）低于室温。发现转变温度随微晶尺寸的增加而升高。磁熵变最大值（ΔS(M)）(max)表现出有趣的行为，且发现其随颗粒尺寸而变化。在1 T磁场下，对于在600℃退火的样品，在213 K时观察到（ΔS(M)）(max)的值为-0.13 J/kg K。此外，在较高的退火温度下观察到（ΔS(M)）(max)值的增加。该研究表明，通过调节锰氧化物的微晶尺寸可以调节钙钛矿锰氧化物的磁熵。
