In the past decade intensive work was invested in multiferroic materials and in particular in BiFeO3, due to its high ferroelectric and antiferromagnetic ordering temperatures and large ferroelectric polarization. Moreover, it was demonstrated that in hybrid Co0.90Fe0.10/BiFeO3 heterostructures, an electric field-induced magnetization reversal could be obtained, opening up avenues for next-generation, low-energy consumption spintronics. The concept relies, however, on a particular configuration of stripes of two variants of 71° ferroelastic/ferroelectric domains in the BiFeO3 underlayer (see Fig. 1), whose electric field-induced switching leads to rotation of the antiferromagnetic domains. The latter are coupled to the ferromagnetic domains in the ferromagnetic CoFe top layer, resulting ultimately in reversal of the direction of CoFe magnetization. Hence, the following questions arise: how can we obtain this particular domain pattern in BiFeO3 in a controlled manner? How stable are these stripes of 71° ferroelectric domains upon repeated switching under electric field pulses?
We subjected epitaxial BiFeO3 films that exhibit stripe domains (Figure 1) to fatigue experiments. Metal contacts were evaporated through a shadow mask on top of epitaxial BiFeO3/SrRuO3 heterostructures grown on SrTiO3(100) crystals. The polarization was switched by applying electric field pulses perpendicular to the BiFeO3 film surface. After repeated switching cycles we removed the top metal electrodes by wet etching the metal and investigated the ferroelectric domains patterns in those areas, monitoring the changes in the domain patterns as a function of the number of switching pulses. The domain patterns were investigated by piezoresponse force microscopy (PFM), both on the pristine BiFeO3 film and on the switched areas where the capacitor had formerly been located.