Growth of high quality Fe thin films : A study of the effect of mismatch strain on the physical properties of Fe

Sammanfattning: The work in this licentiate is devoted to investigating the epitaxial growth of thin Fe layers on MgAl2O4 (001) and MgO (001) substrates using dc magnetron sputtering. The aim is to qualitatively and quantitatively determine the crystal quality of the grown Fe layers depending on their thickness, substrate material, and selected deposition parameters. The effect of the crystal quality on the magnetic and electronic transport properties is discussed. The structural characterization of the epitaxial Fe thin films is carried out by x-ray reflectometry and diffraction as well as transmission electron microscopy. X-ray scattering measurements and analysis with related models allow for a quantitative determination of layering, crystal quality, and strain profiles in the growing Fe. Magnetic properties are determined using a combination of longitudinal magneto-optical Kerr effect measurements, Kerr microscopy, and scanning electron microscopy with polarization analyser. Electronic transport properties are characterized by four-point probe measurements of the thin films. The epitaxial growth of Fe is found to be highly substrate dependent: Fe layers grown on MgAl2O4 have a significantly higher crystal quality, as compared to Fe grown on MgO. The difference in crystal quality is attributed to different strain states in Fe, which is supported by theoretical calculations of the critical thickness on both substrates. Moreover, an anomalous elastic response in Fe at the thin film limit is found. The magnetic properties of Fe are weakly reflecting the differences in crystal quality of the Fe layers. However, the difference in crystal quality affects the electronic transport properties. The results of this study on epitaxial Fe layers can provide insights into strain and defect engineering in Fe thin films, which can additionally serve as model systems for finite size effects.