It turns out that cobalt has the highest MAE of the ferromagnetic elements, which is why it is the material of choice for magnetic data recording.
The trouble is that the MAE of any material depends on its structure. The grains of cobalt in state-of-the-art data storage consist of about 50,000 atoms in a hexagonal close packed structure. In this formation, cobalt has an MAE of 0.06 meV per atom.
It should be possible to reduce the size of these grains to about 15,000 atoms, but in grains any smaller than that, it becomes impossible to guarantee the hexagonal close packing. And without that structure, the MAE drops precipitously and the data is lost over much shorter timescales.
What Xiao and co have found is a way to trick cobalt dimers into thinking that they’re in a hexagonal close packed structure. Their idea is to attach the dimers to a hexagonal carbon ring such as benzene or graphene. In this scenario, one of the pair of cobalt atoms bonds with the carbon ring, and the magnetic field between the cobalt atoms can be switched by applying a weak magnetic field and a strong electric field.
Now in this setup, the MAE of cobalt is calculated to be about 100 meV. And while chemical bonds usually have a significant effect on the MAE, Xiao and co say that the carbon hexagons do not.
If they’re right, carbon ring storage should allow engineers to access this extraordinary stability, and that could lead to fantastically long-lived memory.
It should also allow much higher memory density too. The cobalt grains now used in magnetic storage are roughly 8 nm across. Benzene rings, on the other hand, are merely 0.5 nm across.
The only question now is whether this team’s calculations hold true in the real world.
Ref: arxiv.org/abs/0906.4645: Co Dimers on Hexagonal Carbon Rings Proposed as Subnanometer Magnetic Storage Bits