In the future computer memory could be made from molecular magnets say European researchers.

Eliseo Ruiz and Santiago Alvarez, University of Barcelona, Spain and colleagues in Germany have created a mathematical model to improve single molecule magnets (SMMs) - molecules that magnetise in a particular direction. Ruiz plans for the SMMs to be used in the future to manufacture computer memory, with a single molecule representing each digit in a binary string: 1 if magnetised in one direction, 0 if magnetised in another.

A large hurdle in the way of using SMMs in computer memory is that to store their magnetisation reliably they need to be kept below a critical temperature, which is usually only a few degrees above absolute zero. 'In order to store information in any magnetic material one needs an energy barrier preventing the flip of the direction of the magnetisation,' explained Jens Kortus, TU Bergakademie Freiberg, Germany, who collaborated with the Ruiz team.  SMMs with much higher critical temperatures are needed to make their use in memory practical, said Ruiz. 

The critical temperature of the molecule depends on its spin, or angular momentum, and its magnetic anisotropy, the energy needed to change the direction of the magnetisation. Previous attempts to design SMMs have looked at optimising their spin, as more is known about how to control this, explained Ruiz.

Ruiz's team used mathematical models to study ways of optimizing both spin and magnetic anisotropy, and found it was not possible to achieve both at the same time. 'While the total spin of a molecule can be optimized, our results indicate that what we gain by increasing the spin is lost through a decreased magnetic anisotropy,' said Ruiz. Optimising spin might not be the best way to make a good SMM, he added. 'Our results suggest a different strategy should be pursued searching for new molecular architectures based on metal atoms with high magnetic anisotropy.'

Clare Boothby