Progress in perovskite nickelate research

Perovskite nickelates (RNiO3, where R is rare earth or a heavy metal such as Tl or Bi) display sharp metal–insulator transitions, unusual magnetic order, charge order and, perhaps, orbital order. Furthermore, there are strong reasons to believe that some of them may be magnetoelectric multiferroics. In this article the author reviews recent research perovskite nickelates, highlighting the important role that thin film research has contributed to our understanding of their properties. A special emphasis is placed on open questions and highly topical issues such as whether or not nickelates have orbital order, and whether or not (and why) some of them may be multiferroic.