Electron diffraction study of the plastic relaxation of MgO epitaxially grown on BCC FeV(001) alloys by varying the lattice mismatch

•misfit dislocations evidence in MgO barrier epitaxially grown on magnetic electrodes by electron diffraction (RHEED) in real time (video available).•The RHEED patterns modifications induced by the dislocations are highlighted by using a subtraction images process (video available).•Explanation of the RHEED patterns modification using kinematic theory•Playing with the misfit between MgO and Fe1-xVx by varying x to accurately measure the critical thickness for plastic relaxation dependence with the misift.

The epitaxial growth of MgO on Fe1 − xVx buffer layers with adjustable lattice parameter is studied by electron diffraction (RHEED) in real time. At the onset of plastic relaxation in the MgO layer, a clear splitting of the diffraction rods is observed in 〈110〉 directions, as well as an increase in their length in the 〈100〉 directions. Splitting along 〈100〉 is also made visible through image background subtraction. These features originate from the surface strain above misfit dislocations, as previously proposed to account for satellite spots in LEED measurements. This explanation is supported by simulations of the diffraction patterns using kinematic diffraction theory. Observation of the diffraction rods splitting is shown to be a powerful way to check the presence of dislocations in MgO tunnel barriers and to accurately determine the critical thickness of plastic relaxation.

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