Strain driven monoclinic distortion of ultrathin CoO films in   CoO/Pt(001) and exchange-coupled CoO/PtFe/Pt(001) systems
  The structure and strain of ultrathin CoO films grown on a Pt(001) substrate and on a ferromagnetic PtFe pseudomorphic layer on Pt(001) have been determined with insitu 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(111) surface. A refined x-ray diffraction analysis reveals a slight monoclinic distortion at RT induced by the anisotropic stress at the interface. The tetragonal contribution to the distortion results in a ratio c/a > 1, opposite to that found in the low temperature bulk CoO phase. This distortion leads to a stable Co2+ spin configuration within the plane of the film. 
Anne D. Lamirand and Maurizio De Santis and Marcio M. Soares and Aline   Y. Ramos and Stephane Grenier and Helio C. N. Tolentino
cond-mat.mes-hall cond-mat.mtrl-sci