Single-molecule magnet created from depleted uranium

Researchers from Nottingham University have created a single molecule magnet based on two linked atoms of the element.

‘A 50mg sample, which occupies a physical space of about 0.5cm³, would hold 10¹⁹ molecules,’ said study lead Prof Stephen Liddle of Nottingham. ‘Imagine if each one of those could be a zero or a one on your data-storage device — bearing in mind that a terabyte is 10¹² [bytes] — that’s a lot of storage in a very small space.’

Traditional hard disks use magnetic domains on the scale of microns that act as tiny polar magnets that store binary data according to whether they are orientated in a ‘north or south’ position.

Creating even smaller single-molecule magnets relies on achieving two properties: a high-spin ground state, which essentially refers to the magnetic moment, and anisotropy, which is the tendency to organise in a polar orientation.

There has been some success creating single-molecule magnets with the so-called transition metals and lanthanide metals. However, the former show good moment but poor anisotropy while the latter display the reverse situation.

Liddle found that a new compound based on depleted uranium seemed to have acceptable moment and anisotropy — something of a compromise between the transitions and lanthanides.

The depleted uranium used is not radioactive and is essentially the product left behind after the uranium-235 isotope has been separated from the non-radioactive uranium-238 during enrichment for nuclear-power and weapons applications.

Liddle cautioned that, while progress is being made in terms of operating temperatures, the device still needs to be cooled to around 40 Kelvin (-233°C) to keep its magnetism.

‘Just imagine if you had a hard drive where if you had a hot day it just wiped itself. And as far as single-molecule magnets are concerned, a hot day is anywhere from 2 Kelvin all the way up,’ he said.

The team is now investigating ways of creating larger clusters that may have higher operating temperatures.