The dependence of frozen-in mechanical strain on thermal expansion behavior of ferromagnetic bulk metallic glasses

Bulk metallic glasses (BMGs) are amorphous alloys obtained by kinetic freezing of the corresponding metallic melts. They lack the long-range order (LRO). This gives them very specific properties, most of which are not fully understood (nor investigated). Among them, the ferromagnetic BMGs show a peculiar effect; this is the invar effect. The coefficient of thermal expansion (CTE) is anomalously low as long as the BMG is in the ferromagnetic state, increasing up to one order of magnitude in its paramagnetic state. This it is an intrinsic property of the magnetic interactions of Fe – Fe pairs and not an emergent phenomenon of complex magnetic arrangements. Additionally, the mechanical strain influences the macroscopic invar effect. Furthermore, the changes in the second and third neighborhood shell (i.e. the medium-range order MRO) play also an important role on the global, macroscopic behavior.

块体金属玻璃（Bulk Metallic Glasses, BMGs）是通过对对应金属熔体实施动力学冻结而得到的非晶合金。这类材料不具备长程有序（Long-Range Order, LRO）结构，因此拥有一系列独特性能，其中多数尚未被充分阐释，甚至未得到系统性研究。在块体金属玻璃中，铁磁性体系会呈现出一种特殊效应——因瓦效应：当该材料处于铁磁态时，其热膨胀系数（Coefficient of Thermal Expansion, CTE）异乎寻常地低；而当材料转变为顺磁态时，热膨胀系数可提升一个数量级。该效应是铁-铁原子对磁相互作用的本征特性，而非复杂磁排布所催生的涌现现象。此外，机械应变会对宏观因瓦效应产生显著影响。进一步而言，原子第二与第三近邻壳层（即中程有序（Medium-Range Order, MRO））的变化，同样对材料整体的宏观行为发挥着关键作用。