First-principles investigation of phase-change effects in multiferroics*

Using first-principles calculations we have characterized new phases of bulk multiferroic materials that are close in energy to the ground state, but that display very different properties. This suggests that the application of electric fields could induce phase changes that would involve large effects of different kinds. In particular, (i) we have found stable supertetragonal bulk phases for the prototype multiferroic bismuth ferrite [Di\'eguez {\em et al}, Phys.~Rev.~B {\bf 83}, 094105 (2011)], and (ii) we propose to use a solid solution of bismuth ferrite and bismuth cobaltite to create a material where it is possible to switch between two very different phases in a way that involves strong piezoelectric, electric, and magnetoelectric effects [Di\'eguez and \'I\~niguez, Phys.~Rev.~Lett. {\bf 107}, 057601 (2011)].