used plain STO and conducting 0.2 % atomic

Wang et al. (1) recently reported multi-ferroic behavior, with ferromagnetic and fer-roelectric polarizations that are both large at room temperature, in thin strained films of BiFeO 3 (BFO). Although at room tempera-ture, bulk BFO is ferroelectric (2) and anti-ferromagnetic (3–5), Wang et al. (1) reported that a 70-nm film shows both an enhanced ferroelectric polarization (90 mC cm–2) and a substantial magnetization (1 m B /Fe). This remains the only report of a robust room-temperature multiferroic and suggests the potential for novel devices that exploit the anticipated strain-mediated magnetoelectric coupling between the two ordered ground states. In this Comment, we argue that epi-taxial strain does not enhance the magneti-zation and polarization in BiFe