The team at Hokkaido University's Research Institute for Electronic Science investigated the possibility of using a magnetic signal along with the electronic signal to allow double the storage capacity in these ‘multiplex writing/reading’ devices. In addition to the binary 0/1 method of storing information, this would add an A/B store for the information as well. To do this would require finding a material that can switch back and forth from a magnetic to a non-magnetic state.
Using two forms of strontium cobalt oxide with different oxygen content, the device can be switched from an insulating/non-magnetic state to a metallic/magnetic state simultaneously by electrochemical oxidation/reduction reaction at room temperature in air.
The team investigated two forms of strontium cobalt oxide (SrCoOx): one is an insulating non-magnet while the other is a metal magnet. By changing the oxygen content in this compound, the team could cause it to switch between the two forms. However, the two methods currently available to do this have big drawbacks. One method requires using a high temperature heat treatment, making it impossible to use in devices that work at room temperature. The other method involves using a dangerous alkaline solution, which would require a device that is sealed so that the solution does not leak. This method is difficult to miniaturise and is thus not suitable for information storage devices.
The team developed a new method to use strontium cobalt oxide safely at room temperature in air. They applied a sodium tantalate thin film, which can be used at room temperature without leaking alkaline solution, over layers of strontium cobalt oxide. When a 3V current was applied, the insulating form of SrCoO2.5 reversibly switched to its metal magnet form, SrCoO3, in three seconds. By comparison, current devices can store information in 0.01 seconds.
The scientists say that making the device smaller would shorten the time needed for the compound to switch between an insulator and a magnet, allowing the storage of an even larger amount of information in mobile devices, for example.
