Making a storage mountain out of a molecule

Depleted uranium and a magnetic story

Nottingham university boffins have devised a depleted uranium molecule that keeps a constant magnetic state and is many times smaller than bits on hard disk drives, promising 1,000-fold increases in hard drive capacity - if it can be turned into a product before solid state storage takes over.

The Notts team, led by Dr Steven Liddle, created a depleted uranium molecule built from two uranium atoms with a bridging molecule of toluene and termed it a single molecule magnet (SMM). Liddle's Nature Chemistry paper ($32 fee) talks of a "delocalized arene-bridged diuranium" SMM. A video, featuring a boffin with a Back To The Future hair-style - we're not joking - provides the following chemistry name for the molecule - bis(bis(N-trimethylsilyliminodiphenylphosphorano)methane uranium dodo)toluenediide.

Uranium single molecule magnet

The Uranium molecule used in the single molecule magnet.

It holds its magnetic state stably if kept at a low temperature, around two degrees above absolute zero. Such single molecule magnets are a thousand or more times smaller than the few hundred nananometres wide magnetic grains found in today's fourth generation perpendicular magnetic recording (PMR) media used on hard disk drives. However their magnetic stability breaks down as temperatures climb towards everyday room temperature. The temperature level dividing the stable from the unstable magnetic state is called the blocking temperature.

Best of both worlds

Liddle said: "The inherent properties of uranium place it between popularly researched transition and lanthanide metals and this means it has the best of both worlds. It is therefore an attractive candidate for SMM chemistry, but this has never been realised in polymetallic systems which is necessary to make them work at room temperature.”

He thinks that if the spin state of the molecule is increased then this will lift the blocking temperature, and the way to do that is to add more uranium atoms to it.

There are other problems. Unless the paper's costly full text in Nature Chemistry discusses it there is no method described to change the magnetism of the molecule. The magnetism comes from the molecule itself, not from an applied burst of electricity, and if it can't be changed then that's the end of the IT storage relevance.

Let's assume that that is not a problem though, and that there is a way to do it. Another problem is one of timing. It's going to take years to do the research to find a SMM that's stable at room temperature, to find a way to change its magnetic state, and then to devise recording heads and media that use this technology at an affordable price, and that is a whole huge separate can of worms.

Let's say it is 1,000 times denser areally speaking than current hard drives; what does that mean? The I/O density will be abysmally atrocious. Just how long will it take to backup a 3 petabyte drive with one read head per platter surface? We should envisage a time scale in days unless the spin speed and/or the number of read/write heads is increased. As for RAID re-builds, forget it; we're talking weeks.

Then there is the problem of controlling read/write head movements a thousand times more precisely than we do at the moment. Frankly, the El Reg storage desk thinks this is bonkers; the chemistry boffins obviously know diddly squat about the practicalities of hard disk drive electro-mechanics and RAID rebuilds. This SMM stuff isn't for spinning disks, it's a solid state technology if ever we saw one.

Liddle said SMM study could also help "realise high performance computing techniques such as quantum information processing and spintronics.” ®

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