Regensburg 2022 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 30: Liquid and Amorphous Metals
MM 30.6: Talk
Thursday, September 8, 2022, 11:45–12:00, H46
Origin of the Invar effect in Fe-based bulk metallic glasses — •Alexander Firlus1, Mihai Stoica1, Stefan Michalik2, Robin E Schäublin1, and Jörg F Löffler1 — 11 Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland.2 — 2Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK
Generally, metals, including most ferromagnetic ones, have a constant coefficient of thermal expansion (CTE). However, a few magnetic alloys show an anomalously low CTE below their Curie temperature. At the Curie temperature it increases abruptly by up to one order of magnitude. This effect is known as the Invar effect. While it is rare in crystalline alloys, it is universally observed in ferromagnetic Fe-based bulk metallic glasses (BMGs). To this day, it is still unclear in which way the amorphous atomic arrangement creates the Invar effect and how it manifests at the atomic scale.
In this work we studied BMGs with only one magnetic atom species, Fe, by in-situ high-energy X-ray diffraction. This allows us to measure the thermal expansion at the atomic scale and to associate it with specific atomic pairs. Fe-Fe pairs are found to be responsible for the Invar effect at the atomic scale. Moreover, also full atomic shells, which contain all atomic species, show an abrupt increase in their thermal expansion. This proves that the Invar effect is not just a macroscopic effect but has clear origins at the atomic scale.