电场调控一级磁相变合金磁热效应的非易失性研究

Room-temperature magnetic refrigeration technology based on giant magnetocaloric effects of the first-order magnetic-phase-transition alloys has received lots of attention due to the advantages of environmental protection, high efficiency, energy saving and so on. The electric-field-controlled magnetocaloric effects with the strain-mediated mechanism can remarkably expand the refrigeration region near room temperature. However, there are two issues as follows: (1) The regulation is volatile. (2) The refrigeration region is single. To solve these problems, we carry out the research on non-volatile electric-field-controlled magnetocaloric effects in first-order magnetic-phase-transition-alloy ribbon/(011)PMN-PT laminate heterostructure in this project. Applying a unipolar electric field across the (011)PMN-PT substrate by the magneto-electric coupling effect can realize the non-volatile manipulation on the magnetocaloric effect of magnetic-phase-transition alloy. It is necessary to clarify the relation among the unipolar electric field (direction and amplitude), non-volatile strain and refrigeration region. The influence of non-volatile strain on magnetocaloric effect is illuminated. Through this project, multilevel and stable non-volatile strain may be obtained, which would achieve more and wider refrigeration temperature regions. This work may provide the experimental evidence for the development of multiple refrigeration regions.

以一级磁相变合金巨磁热效应为基础的室温磁制冷技术因具有绿色环保、节能高效等优点而备受关注。基于应变传递机制的电控磁热效应在室温附近能够显著拓宽制冷区间，但仍存在以下两个问题：(1)调控是易失性的；(2)制冷温区单一。为了解决这两个问题，本项目拟在一级磁相变合金条带与(011)PMN-PT压电衬底组成的层状异质结构中开展非易失性电控磁热效应的研究。即对(011)PMN-PT压电衬底施加单极电场，通过应变为媒介的磁电耦合效应，实现对磁相变合金磁热效应的非易失性调控。厘清单极电场（方向和幅值等因素）与非易失性应变、制冷温区的关系，阐明非易失性应变对磁热效应的影响。通过本项目的研究可获得多态的、稳定的非易失性应变态，从而实现更多、更宽的制冷温区，为多区域的制冷奠定实验基础。

本项目研究了外加不同电场并撤去电场后对NiCoMnSn/PMN-PT 异质结构磁性的调控以及对（011）取向的PMN-PT衬底产生剩余应变的影响。当施加非对称双极电场（1.4 kV/cm和1.8 kV/cm）时，剩余应变随电场变化的曲线表现为滞后响应。当电场恢复到零时，应变并没有恢复到0状态，表示出非易失性行为。通过适当利用矫顽场附近的电场，可以在PMN-PT衬底中实现不同的非易失性剩余应变态。并且不同的非易失性剩余应变状态可以通过控制扫描电场的路径进行可逆切换。通过施加和撤去不对称双极电场，非易失性应变使得NiCoMnSn条带的相变温度向更高的温度移动。当电场作用在PMN-PT衬底上时，由于反向压电效应会产生压缩应变。这种应力倾向于稳定体积较小的马氏体相，从而导致马氏体相变温度的升高。利用Maxwell关系计算了在0-2 T磁场范围内不同的非对称双极电场作用下的磁熵变(ΔSM)，在不施加非对称双极电场的情况下，Ni-Co-Mn-Sn条带在309 K时的ΔSM峰值为24.6 J/kg K。当施加不对称双极性电场1.4和1.8 kV/cm时，ΔSM峰值减小，但峰值温度分别升高到311 K和313 K。将1.8 kV /cm非对称双极电场应用到 Ni-Co-Mn-Sn /PMN-PT异质结构中，有效制冷温度区从6K 扩宽到10 K，表明通过施加电场可以获得多态的、稳定的非易失性剩余应变态，从而实现更多、更宽的制冷温区，为多区域的制冷奠定实验基础。