French chemists are looking at an ancient dye as a potential switch that could boost the storage capacity in modern computers.

A compound in Prussian Blue, so named because it was used to dye uniforms for the Prussian army, can be magnetized — which makes it usable as a switch — by applying light, and turned back with heat, University of Paris researchers said Thursday.

"Such compounds, which can memorize binary information, could be used as storage bits for future computers," they said in a release, calling their research "an essential first step" in using atoms to store data.

That is important because the demand for storage space is increasing dramatically, and any technology that shrinks the size of storage systems will boost the capacity of computers.

The researchers replaced some of the iron atoms in Prussian blue with cobalt. When illuminated with a red light at -150 C, the compound shifts from being non-magnetic (off) to magnetic (on). The change is stable, but can be reversed with heat.

This magnetism is due to the transfer of an electron from the cobalt to the iron, with light providing the impetus, while the electron moves back when heat is applied, the researchers said.

"Structural Rearrangements Induced by Photoexcitation in a RbCoFe Prussian Blue Derivative" was published in Angewandte Chemie International Edition on Jan. 9 by Christophe Cartier dit Moulin, Guillaume Champion, Jean-Daniel Cafun, Marie-Anne Arrio and Anne Bleuzen.