中文摘要：

利用固相烧结的方法制备了La0.67Ca0.33Ti0.01Mn0.99O3磁致冷材料。室温XRD分析表明该材料主要由主相的正交钙钛矿结构锰氧化物和少量La2O3杂相构成。利用VSM测量了样品在磁场下随温度变化的磁化曲线（M-T曲线）和居里温度附近的等温磁化曲线（M-H曲线）,通过M-H曲线的一阶导数可得到样品的居里温度Tc（139 K）,从不同温度的等温磁化曲线（M-H）计算得到材料在1.5 T下的最大磁熵变ΔSM=0.8 J.（kg.K）-1,由M2-H/M的Arrott曲线表明La0.67 Ca0.33 Ti0.01 Mn0.99 O3相变类型属于二级相变。由于二级相变不伴随晶格体积的变化和潜热的释放,仅是磁性材料磁畴从无序-有序的连续变化,所以二级相变的磁熵变可能较小,但是由于它是个连续的变化过程,发生相变的温区较大,造成的损耗较小。Ti4＋离子的掺杂取代的是原有晶格中Mn4＋离子（B位）的位置,两者之间不同的离子半径使得晶格发生Jahn-Teller畸变,同时降低了Mn4＋的浓度,使得Mn4＋与Mn3＋离子之间的双交换作用减弱,铁磁耦合作用减小,导致居里温度降低。该材料体系由于二级相变的温度区间较大,表明材料潜在的致冷能力较强,因此具有较好的应用前景。

英文摘要：

The La0.67Ca0.33Ti0.01Mn0.99O3 samples were prepared by the conventional solid reaction method.The X-ray diffraction pattern at room temperature demonstrated that the samples were consisted of major orthorhombic perovskite structure and little impurity of La2O3.The magnetization curves（M-T plot） were measured by VSM and Curie temperature at Tc=139 K was obtained by first derivative of the M-T plot.The maximum magnetic entropy（ΔSM） calculated from the magnetization isotherms under an applied external magnetic field of 1.5 T was estimated to be about 0.8 J ·（kg · K）-1.Second-order magnetic phase transition of the sample was revealed by Arrott plot.Since the second-order transition was only magnetic domain from disorder to order without volume change and latent heat release,the magnetic entropy and losses in the samples could be lower.However,the wide temperature range might be originated from the continuous change of the phase transition.The decline of Curie temperature and magnetic entropy were derived from the weakening of ferromagnetic coupling between Mn4＋ and Mn3＋,where Mn4＋ content and Jahn-Teller distortion were lower.The results could be supported by the fact of Ti4＋ ions substituting the Mn4＋ ions（B-site）.In terms of their wide range of temperature,the samples could have excellent prospect in the refrigerant application.