Weak Ferromagnetic b.c.t. Iron Phase in (100) FeIr Superlattices

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Abstract
In this paper, the synthesis of Fe in a new structure in (100) FeIr superlattices grown by Molecular Beam Epitaxy is reported. The magnetic properties of this new phase are also presented. A two-dimensional growth up to 4 planes at 400 K and 10 planes at around 250 K is observed by RHEED oscillations. Electron diffraction also shows that the Fe lattice is pseudomorphic to the Ir one during the 2D growth, and relaxes to the b.c.c. structure for larger thicknesses. RHEED, X-ray diffraction and EXAFS analyses show that the Fe structure is body-centred tetragonal with a c/a ratio around 1.25. This phase is observed to be non-magnetic at room temperature but ferromagnetic order occurs at low temperature. A variation of the average moment per atom with the Ir thickness is observed, which can be explained by a variation of the Fe volume using a simple elastic model.