Strain driven monoclinic distortion of ultrathin CoO films in the exchange-coupled CoO/FePt/Pt(0 0 1) system.

The structure and strain of ultrathin CoO films grown on a Pt(0 0 1) substrate and on a ferromagnetic FePt pseudomorphic layer on Pt(0 0 1) have been determined with in situ and real time surface x-ray diffraction. The films grow epitaxially on both surfaces with an in-plane hexagonal pattern that yields a pseudo-cubic CoO(1 1 1) surface. A refined x-ray diffraction analysis reveals a slight monoclinic distortion at RT induced by the anisotropic stress at the interface.