Storage of larger and larger quantities of data is constantly taking up smaller and smaller amounts of physical space. But what about storing data in a single molecule? Since the early 1990s single molecule magnets (SMMs) have been explored as a means of data storage and recent research at the University of Nottingham has produced a uranium based molecule which will hold its magnetism at low temperatures giving it data storage potential.
Whereas in an everyday bar magnet the magnetism is held by the electron spins of many molecules, an SMM involves only the spin of the electrons of one molecule. A good SMM has a relatively strong electron spin and the property of anisotropy, a preference for a direction of spin. Transition metals such as iron and manganese found in the middle of the periodic table have a high spin property but low anisotropy meaning that they do not stay in the same spin state and are unable to store data. Other metals have higher anisotropy but are bonded such that the molecules do not communicate with each other, ruling out the potential for creation of large data storage systems.
Uranium is only intermediate in terms of both spin and anisotropy but could be a “happy medium” suggests Dr Steve Liddle a Research Fellow of the Royal Society and Associate Professor at the University of Nottingham. His research has produced a molecule constructed from two uranium atoms with a toluene bridge linking them so that the uranium atoms can “talk” to each other.
Currently, SMM data storage only works at temperatures a few degrees above absolute zero. Above this temperature, known as the blocking temperature, the electrons do not hold their spin direction. This of course means that real world applications are a long way off: “a hard drive that on a hot day wipes itself, that would be no good” says Liddle.
Dr Liddle points out that another of the problems with using a hard drive made from SMMs is that it could be thousands of terabytes in size and would take weeks to back up. However, he stresses the importance of this fundamental research in pushing back the frontiers, so that, though the uranium atoms he currently works on may never be seen in a desktop computer, other metals might be used and we might find more practicable options for SMM data storage. Liddle’s research is about exploring the way the molecules behave, what happens when more of them are linked together and trying to increase the blocking temperature.
Written by Alex Jenkin