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.