Theoretical prediction of the giant magnetocaloric effect in Ni40Co10Mn40Sn7Al3 Heusler alloy.

By using ab initio calculations and Monte Carlo simulations, the influence of the small amount of Al on magnetic and magnetocaloric properties of Ni-Co-Mn-Sn Heusler alloy is studied. First-principles calculations have shown that addition of Al leads to an increase in the energy difference between ferromagnetically (FM) ordered austenite and ferrimagnetically (FIM) ordered martensite. The observed tendency points to an increase in the martensitic transformation temperature (Tm) in accordance with the relation ΔE ~ kBTm. The calculated exchange coupling constants, especially for martensite, exhibit the longrange oscillation behavior showing the strong competition between ferromagnetic and antiferromagnetic interactions. By the help of the Hamiltonian model (Potts-Blume-Emery-Griffiths), the temperature dependences of the magnetization, tetragonal deformation, and adiabatic temperature changes for magnetic field variation are obtained. It is shown that the addition of few percent of Al into Ni-Co-Mn-Al leads to increase of the inverse magnetocaloric effect.

本研究采用从头算（ab initio calculations）与蒙特卡洛模拟（Monte Carlo simulations），系统探究了微量铝（Al）对Ni-Co-Mn-Sn型赫斯勒合金（Heusler alloy）磁学与磁热性能的影响。第一性原理计算结果表明，铝的掺入会增大铁磁（FM）有序奥氏体与亚铁磁（FIM）有序马氏体之间的能量差。该变化趋势符合ΔE ~ kBTm的关系式，预示着马氏体转变温度（Tm）将随之升高。计算得到的交换耦合常数（尤其针对马氏体相）呈现长程振荡行为，体现出铁磁与反铁磁相互作用间的强烈竞争。借助Potts-Blume-Emery-Griffiths哈密顿量模型，我们得到了磁化强度、四方畸变以及磁场变化下绝热温变的温度依赖特性。研究显示，在Ni-Co-Mn-Al合金中掺入少量铝可增强其反向磁热效应。