磁致冷材料的制冷能力由其磁熵变、制冷工作温度区间和磁滞后综合决定，针对镍锰基合金制冷温度区间窄、磁滞后大的问题，本项目以镍锰镓多晶纤维为研究对象，通过设计纤维复合化和引入磁-结构部分耦合相变两种方法宽化制冷工作温度区间，并结合一维纤维材料界面可动性强滞后小的特性，优化其综合磁热性能。基于镍锰镓相变温度依赖成分以及纤维比表面积大的特征，采用热处理调节纤维相变温度和一级相变宽度，研究热处理工艺对相变温度的影响规律，获得磁-结构相变部分耦合状态的纤维。研究晶粒尺寸和界面等对纤维滞后的影响，获得有效降低相变热滞后（< 3K）和磁滞后（平均值 < 3J/kg）的热处理方法，并阐明其微观机制。研究复合化状态和磁-结构部分耦合状态纤维的磁热性能，最终实现50 kOe下磁致冷温度工作区间> 50K且制冷能力> 300J/kg，并阐明内在机理。本项目的设计思想可为类似小尺寸材料的磁热性能优化提供技术途径和导向。

Magnetic entropy change, working temperature interval and magnetic hysteresis loss of magnetic refrigerant material determines its magnetic refrigerant capacity. In view of the narrow working temperature interval and large magnetic hysteresis loss of the Ni-Mn-based alloys, magnetic refrigerant capacity optimization was studied in polycrystalline Ni-Mn-Ga microwires in the present project. Two methods of compounding microwires with different transition temperatures and introducing partially coupled magnetic-structural transition into the microwires were designed to enlarge the working temperature interval. Combined with the decreased hysteresis loss attributing to the enhanced grain free surface of the one dimensional microwires, improvement of magnetic refrigerant capacity in Ni-Mn-Ga alloy was expected. Based on the compositional dependence of the transformation temperatures in Ni-Mn-Ga alloys and the increased specific surface area of the microwire, different kinds of heat treatments were applied to adjust the transformation temperatures and first order transition range of the microwires. The effect of heat treatments on the transformation temperatures was investigated and several partially coupled states were expected. Effect of grain size and interfaces on the hysteresis of the microwires was studied. Effectively reduced thermal hysteresis (< 3K) and average magnetic hysteresis (< 3 J/kg) were expected after certain heat treatments, and the micro-mechanism of the reduction was studied. Magnetocaloric effect of the compounds and the partially coupled microwires was investigated. Working temperature interval > 50 K and refrigerant capacity > 300J/kg were expected under 50 kOe, and the inner mechanism was addressed. The novel design idea of the present project provides technical methods and guidance for the magnetocaloric effect optimization of similar small size refrigerant materials.