Structure and chemical order in FeRh nanolayers epitaxially grown on MgO(0 0 1)

FeRh nanolayers, 2–5 nm thick, were deposited on a MgO(0 0 1) substrate by dc-magnetron co-sputtering of elemental targets. The growth temperature was varied in order to promote the formation of highly oriented FeRh nanodots. The evolution of the morphological and structural characteristics was analyzed by high-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations of plan-view and cross-sectional specimens. FeRh alloy adopts a Volmer-Weber (3D) growth mode but well-separated nanodots required high temperature (typically 700 °C). We show that, whatever the growth temperature, the as-deposited nanolayers display the face-centered-cubic (fcc) structure of the paramagnetic γ‐FeRhγ‐FeRh phase. The occurrence of the chemically ordered body-centered cubic phase, which displays the more interesting properties for technological applications, required a post-annealing step. Chemically ordered FeRh nanodots were thus formed after a 30-min post-annealing in films deposited at 200 °C. Partial dewetting of these films was also observed during the annealing step.