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43122-AC5
Dislocations in Thin Films of Ferroic Oxides

S. Pamir Alpay, University of Connecticut

We have continued our theoretical analysis on dislocations in ferroelectric thin films based on the findings from last year. It was shown that via a qualitative comparison using thermodynamic and electrostatic analysis concluding that the misfit segments of dislocations are more detrimental than the threading segments. this work has been published in Integrated Ferroelectrics, vol. 83, pp 67-80 (2006).

We have also looked into defect mechanisms in graded ferromagnetic hexaferrites. This was an experimental effort, carried out in collaboration with G. Lawes (Wayne State) and Gopal Srinivasan (Oakland Un.). We have investigated the internal magnetic field induced by a spatially varying magnetization in a compositionally graded ferromagnet. There is a variation in saturation magnetization of 30 emu/g over a sample thickness of 2.5 mm. The DC magnetization shows a small anisotropy depending on the direction of the external magnetic field relative to the grading direction. This contribution from a grading induced magnetic field is more pronounced in AC susceptibility measurements. We find a shift in magnetic properties corresponding to an internal magnetic field of 30 Oe. Should dislocations or other defects such as vacancies form in ferromagnetic materials, a similar built-in field as in the case of graded samples can be expected. This work was published in Applied Physics Letters, vol. 90, art. number 062502 (2007).

We have also provided a comment on a recent computational analysis in Applied Physics Letters 90, 236101 (2007).

This grant has resulted in 4 journal publications and 1 PhD degree (Dr. Burc Misirlioglu). Dr. Misirlioglu has received the prestigious Alexander von Humbolt Post-Doctoral Research Fellowship and is currently working at Max Planck Institut, Halle, Germany.

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