Oxide heterostructures displaying interfacial magnetic order have been the subject of much study but their use is currently limited by low magnetic ordering temperatures. In the May 5 online edition of Chemistry of Materials (DOI: 10.1021/cm200454z), S.-K. Kim at Seoul National University and his colleagues report on the growth of (111)-oriented Sr₂FeRuO₃ superlattices having a robust ordered-double-perovskite structure that display magnetic ordering up to 390 K.

The researchers managed to overcome thermodynamic barriers to (111)-oriented growth by using a thin SrRuO₃ buffer layer deposited on Ti⁴⁺-terminated SrTiO₃ (111) as a template. They then deposited 55 alternating layers of SrFeO₃ and SrRuO₃ to build up a superlattice while maintaining precise structural and chemical control over each layer.

Using a combination of reflection high energy electron diffraction, x-ray diffraction, and transmission electron microscopy, the researchers confirmed the structure of the superlattices. They probed the temperature-dependent magnetization of the structure and found that it possesses a magnetic-ordering (ferromagnetic or ferrimagnetic) critical temperature (T _c) of ~390 K, more than double the T _c of isolated SrRuO₃ and SrFeO₃. They attribute this unusual behavior to band broadening and electron transfer that typically occur in ordered double perovskites, as well as ferromagnetic order stabilized by the addition of Ru⁵⁺ ions.

Ordered-double-perovskite structure of Sr₂FeRuO₃ shows stacking of Ru and Fe ions in (111) planes. Reprinted with permission from Chem. Mater. (May 5, 2011), DOI: 10.1021/cm200454z. ©2011 American Chemical Society.

The researchers said that their (111)-ordered superlattice-growth method may be applied to the growth of different oxide systems to achieve new kinds of room-temperature electronic and magnetic ordering.