Seminar: The ‘irony’ of iron

Through experiments with X-ray scattering, we have been able to identify a new crystal symmetry in iron [1]. The new phase of iron was found to have a tetragonal crystal structure instead of the usual cubic form.

This new iron symmetry arose in a boundary layer between magnesium aluminum oxide (MgAl₂O₄) and a thin layer of iron, which was formed through a process called sputtering. During the sputtering process iron atoms are removed from an iron source with the help of gas plasma and are directed towards a substrate where they begin to form crystals.

Theoretical calculations support these observations and show that the new iron symmetry can arise if the crystals that build up on the substrate are extremely thin, just a few Ångström (0,0000000001 m) in thickness.

The new iron phase has magnetic properties which are significantly different from ordinary iron. It exhibits a reduced magnetic moment and a significantly lower magnetic ordering temperature, that is the temperature at which iron becomes magnetic. For this new phase, the ordering temperature lies at 127 degrees Celsius, compared to 770 degrees Celsius for ordinary iron.

Reference:

[1] A. L. Ravensburg et al., Phys. Rev. Mater. 8, L081401 (2024)