Boundary-induced phase in epitaxial iron layers

We report the discovery of a boundary-induced body-centered tetragonal (bct) iron phase in thin films deposited on MgAl${}_2$O${}_4$ ($001$) substrates. We present evidence for this phase using detailed x-ray analysis and ab-initio density functional theory calculations. A lower magnetic moment and a rotation of the easy magnetisation direction are observed, as compared to body-centered cubic (bcc) iron. Our findings expand the range of known crystal and magnetic phases of iron, providing valuable insights for the development of heterostructure devices using ultra-thin iron layers.