18 95 , 237205 (2005). [32] Vansteenkiste, A., Weigand, M., Curcic, M., Stoll, H., Schutz, G. & Van Waeyenberge, B., Chiral symmetry breaking of magnetic vortices by sample roughness New J. Phys. 11 , 063006 (2009). [33] Pufall, M.R., Rippard, W.H., Schneider, M.L. & Russek, S.E., Low-field current-hysteretic oscillations in spin-transfer nanocontacts Phys. Rev. B 75 , 140404(R) (2007). [34] Mistral, Q. van Kampen, M., Hrkac, G., Kim, Joo-Von, Devolder, T., Crozat, P., Chappert, C., Lagae, L. & Schrefl, T., Current-driven vortex oscillations in metallic nanocontacts Phys. Rev. Lett. 100 , 257201 (2008). [35] Yuasa, S. & Djayaprawira, D.D., Giant tunnel magnetoresistance in magnetic tunnel junctions with a crystalline MgO(001) barrier J. Phys. D: Appl. Phys. 40 , R337 (2007).