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1.5T下的最大磁熵变△SM =0.8 J.(kg·K)-1,由M2-H/M的Arrott曲线表明La0.67Ca0.33 Ti0.01Mn0.99O3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.
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