Fe-Pd-X Thin Film-Polymer Composites for Sensor Applications - First-principles evaluation of magneto-crystalline anisotropy and related intrinsic properties of Fe-Pd-X: optimization of alloy composition

该项目是旨在为传感器应用开发新型磁性形状记忆Fe-Pd-X合金的合作项目的一部分。磁性形状记忆合金(MSMA)近年来备受关注。由于Ni2MnGa的大磁感应应变高达10%，它们在执行器应用中很有价值。然而，由于阻隔力低，这种材料的应用受到了限制。一种有前途的MSMA是Fe70Pd30合金，它具有较小的应变，但显著高于10 Mpa的阻断应力。通过添加第三元素对该合金进行优化是必要的，以促进其在传感器中的应用。在这里，第一性原理计算是为了(I)获得对Fe-Pd合金的本征性质(自发磁化强度、四方形变、磁晶各向异性)的基本了解，以及(Ii)预测如果添加其他元素来产生三元(四元)Fe-Pd-X(-Y)系统的本征性质的变化。虽然在低外场和消失外应力下的场感应变与自发磁化强度成正比，但可达到的最大应变和阻挡应力不可避免地由磁晶各向异性能决定。因此，对这两种本征性质的了解对于判断某一种合金的工艺适用性是必要的。另一方面，MSMA的磁晶各向异性很难测量。因此，对于预期性质的预测和对测量数据的理解，都需要第一性原理计算。

This project is part of a collaboration aiming at new magnetic shape memory Fe-Pd-X alloys for sensor applications. Magnetic shape memory alloys (MSMA) have received much attention in recent years. They are of interest for actuator applications due to large magnetically induced strains of up to 10% in Ni2MnGa. However, application of this material is restricted due to low blocking forces. A promising MSMA is the Fe70Pd30 alloy with smaller strains but significantly higher blocking stresses of 10 MPa. Optimization of this alloy by adding third elements is necessary to facilitate its application in sensors. Here, first-principles calculations are envisaged to (i) gain fundamental understanding of the intrinsic properties (spontaneous magnetization, tetragonal distortion, magneto-crystalline anisotropy) of Fe-Pd alloys and (ii) predict the change of intrinsic properties if other elements are added to produce ternary (quaternary) Fe-Pd-X(-Y) systems. While the field-induced strain at low external field and vanishing external stress is proportional to the spontaneous magnetization, the achievable maximum strain and the blocking stress are unavoidably determined by the magneto-crystalline anisotropy energy. Thus, knowledge of both intrinsic properties is necessary to judge the technological applicability of a certain alloy. On the other hand, the magneto-crystalline anisotropy of MSMA is difficult to measure. Thus, first-principles calculations are needed both for the prediction of expected properties and for the understanding of measured data.