‘Spin doctoring’ a new memory

The team is investigating relationships between a compound’s electron spin arrangement and its transport properties.

Metal-insulator transition (MIT) is a phenomenon in which certain (electricity-conducting) metals make a sudden transition to become (non-conducting) insulators when cooled below a given temperature. Unlike pure insulators and pure conductors, metals with MITs are unstable and hard to characterise. However, says the RIKEN team, complex materials with MITs (such as semiconductors) also form the building blocks for much of our modern computer technology.

Among MIT-exhibiting materials, Cd2Os2O7 (a compound of cadmium, osmium and oxygen) has attracted attention because when it is cooled to 227K (-46°C), it undergoes both a metal-insulator transition and a magnetic transition to a state in which all its electron spins are aligned. Spin alignment, which makes the material magnetic, is useful for a range of applications, including data storage.

The team’s findings show that at 227K, Cd2Os2O7 structures itself into a tetrahedral network of osmium atoms with electron spins in each tetrahedron pointing in one of two directions: all inward, or all outward. The structure is such that the spins cancel each other out, so that the material as a whole is not magnetic.

This suggests that Cd2Os2O7 has the makings of a kind of storage medium, the RIKEN team believe, one whose binary bits of information (‘all-in’ and ‘all-out’ spin arrangements) would be largely unaffected by surrounding magnetic fields.