Magneto-structural fluctuations related to the Invar effect in Fe-based bulk metallic glasses

The crystalline ferromagnetic Fe65Ni35 alloy is known for its very low (almost zero) and constant thermal expansion coefficient below Curie temperature. This effect, named Invar effect, has been found in various ordered and random crystalline alloys. There is no unified explanation of the Invar effect in the field of magnetism and the full understanding is still lacking. A common explanation involves two local atomic arrangements of Fe that differ in their spin configuration and also their volume, however, there is no agreement on the exact nature of these arrangements. Fluctuations between these configurations are said to counteract thermal expansion. Measuring the atomic-scale thermal expansion at cryogenic temperatures will provide insights into their existence and nature of different magneto-structural fluctuations in Fe-based bulk metallic glasses as well as uncovering the influence of rare-earth elements on the Invar effect.