Stabilization of the NiF$_2$ orthorhombic phase in epitaxial heterostructures on CaF$_2$/Si(111) substrates

Epitaxial NiF$_2$ layers have been grown for the first time on CaF$_2$(111)/Si(111) substrates by molecular beam epitaxy. By high-energy electron diffraction and X-ray diffractometry, it has been established that the layers crystallize in the metastable orthorhombic phase and the epitaxial relations at the NiF$_2$/CaF$_2$ heterointerface have been determined: (100)$_{\mathrm{NiF}_2}$ $\parallel$ (111)$_{\mathrm{CaF}_2}$, [001]$_{\mathrm{NiF}_2}$ $\parallel$ $[1\bar10]_{\mathrm{CaF}_2}$.