Multiferroic hetereostructures consist of two types of ferroic materials, typically a ferroelectric and ferromagnet, linked together through interfacial interactions, often a magnetostrictive mechanism¹. In these types of multiferroics the strain associated with the ferroelectric polarization sets a microscopic anisotropy that couples the ferroelectric domains to ferromagnetic domains². These multiferroics offer interesting spin textures that can be controlled by a range of techniques which, if functionalized, could result in lower power spintronic devices.

Here we use multiferroics based on BaTiO₃(111) substrates in which the strain has a heavy dependence on the temperature. Measurements of anisotropy are taken using a Kerr microscope in an optical cryostat. Figure 1 shows that there are three distinct regions of interest corresponding to the different crystal phases of BaTiO₃: tetragonal (T) at room temperature, orthorhombic (O) below 280K and rhombohedral (R) below 190K. The greatest region of anisotropy change is close to room temperature at the orthorhombic phase transition, with another significant region around the rhombohedral transition. This tunability is important when considering the domain structure. Depending on the orientation in which a magnetic field is applied³, the magnetization can rotate in either a head-to-tail (uncharged) or head-to-head (charged) fashion. Figure 2 shows by micromagnetic simulations informed by experiments that it is possible to control domain wall width through temperature alone. Our results show that this change is heavily non-linear with temperature and show the most pronounced change in charged domain walls with a change of ~100% going from the tetragonal to rhombohedral phase. This could be exploited in a temperature activated spintronic device.