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Reliable polarization switching of BiFeO3

As a room temperature multi-ferroic with coexisting anti-ferromagnetic, ferroelectric and ferroelastic orders, BiFeO3 has been extensively studied to realize magnetoelectric devices that enable manipulation of magnetic ordering by an electric field. Moreover, BiFeO3 is a promising candidate for ferroelectric memory devices because it has the largest remanent polarization (Pr>100 μC cm−2) of all ferroelectric materials. For these applications, controlling polarization switching by an electric field plays a crucial role. However, BiFeO3 has a complex switching behaviour owing to the rhombohedral symmetry: ferroelastic (71°, 109°) and ferroelectric (180°) switching. Furthermore, the polarization is switched through a multi-step process: 180° switching occurs through three sequential 71° switching steps. By using monodomain BiFeO3 thin-film heterostructures, we correlated such multi-step switching to the macroscopically observed reliability issues of potential devices such as retention and fatigue. We overcame the retention problem (i.e. elastic back-switching of the 71° switched area) using monodomain BiFeO3 islands. Furthermore, we suppressed the fatigue problem of 180° switching, i.e. loss of switchable polarization with switching cycles, using a single 71° switching path. Our results provide a framework for exploring a route to reliably control multiple-order parameters coupled to ferroelastic order in other rhombohedral and lower-symmetry materials.