La0.65Sr0.2Gd0.15MnO3纳米颗粒的制备及其磁热效应

Synthesis and Magnetocaloric in La0.65Sr0.2Gd0.15MnO3 Nanoparticles

采用Pechini法制备了La0.65Sr0.35–xGdxMnO3系列纳米多晶样品,X射线衍射数据分析表明样品具有单一的菱面体钙钛结构,用扫描电子显微镜观察了样品的形貌,用超导量子干涉仪测量了样品的磁性随外场和温度的变化,确定了样品的Curie温度。发现Gd掺杂量为x=0.15时,Curie温度处于室温附近,根据Maxwell’s关系计算了该样品在不同磁场强度下的磁熵变及相对制冷能力。磁性测量及计算结果表明：制备的样品Curie温度在280～350 K的范围内,随着Gd3＋掺杂浓度增加而下降,其中,La0.65Sr0.2Gd0.15MnO3样品在300 K、H=3.0 T的外场下磁熵变为1.87 J/（kg·K）,相对制冷能力达到215.76 J/kg,由Banerjee判据确定材料在Curie温度附近发生了二级相变。该材料的Curie温度在室温附近并且具有较大的磁熵变及相对制冷效率,所需外场强度适中,性能稳定,适合做室温磁制冷材料。

Polycrystalline perovskite-type manganite La0.65Sr0.2Gd0.15MnO3（x=0-0.2） was prepared by Pechini method. The crystalline phases of the samples were carried out by X-ray powder diffraction with Cu Kα radiation from 20° to 80°. The X-ray diffraction results revealed all the samples exhibits rhombohedra perovskite structure. The morphologies of samples were respected by scanning electron microscope. Magnetic properties and Curie temperature are measured by superconducting quantum interference device. Magnetization as a function of temperature shows that all samples exhibit a paramagnetic-ferromagnetic phase transition at the Curie temperature. The Curie temperature is found to decrease from 350 to 280K upon Gd doping from 0 to 0.2. For x=0.15, the Curie temperature of the sample was determined to be 300 K. The magnetic entropy change deduced from the measured magnetization data using Maxwell relation. The maximum value of isothermal entropy change is found to be 1.87 J/（kg·K） under a magnetic field change of 3 T and about 215.76 J/kg of relative cooling power was obtained near the Curie temperature. The first-order or the second-order on the phase transition of the manganite was distinguished by Banerjee criteria. The high relative cooling power value and the absence of magnetic hysteresis suggest the studied sample can have potential applications for magnetic refrigeration near room temperature.