Disorderly conduct

A new class of perovskite materials with unusual disorder are multiferroic near room temperature

Credit: © 2009 Wiley

Multiferroic phases show both ferroelectric and ferromagnetic properties at the same time. This can allow the control of electric properties by magnetic fields, and vice versa. There are very few examples with this behaviour at room temperature, and the perovskite BiFeO₃ is the best example.

Now, Alexei Belik and colleagues from the National Institute of Materials Science in Ibaraki, Japan, have discovered¹ a new class of materials with multiferroic properties near room temperature. The indium/manganese/iron oxide is synthesized at high temperature and pressure (1,773 K and 6 GPa). All the indium atoms occupy the A sites in an ABO₃ perovskite structure, but not all the manganese and iron sites are on the B sites. Unusually, some of these are on A sites in a random distribution, as are the ones on the B site.

With this level of disorder, it is extremely unusual to get long-range magnetic order, but this is exactly what Belik and colleagues observe. Below 300 K, the material is weakly ferromagnetic, as detected by SQUID measurements and confirmed by Mössbauer spectroscopy. The ferroelectric Curie temperature is high, with no phase transition observed up to 670 K. Although the high-pressure synthesis could prevent the material's wider use, it could be possible to stabilize the structure on a thin film by using substrate effects.