A prototype magnetic memory device that functions without a permanent magnet is presented this week in Nature Communications. The ability to operate without a permanent magnet means that this memory device is easier to downscale in size compared to other magnetic memory technologies.
Magnetic memories generally function using the magnetic fields in two ferromagnetic layers - one layer consisting of a permanent magnet and one layer with adjustable magnetic polarization. These layers can either be in parallel or in antiparallel alignment which changes the ease with which current can pass through the device. But permanent magnets are difficult to miniaturize. To circumvent this problem, Yossi Paltiel and colleagues exploit the recently discovered spin filtering effect in helically twisted organic molecules for their prototype memory. If electrons with spin up or spin down pass through a helical molecule, this effect dictates that it depends on the winding direction of the helix as to which spin passes more easily. When information is written, current is driven through the helical molecules and only electrons with one spin will be ejected on the other end. This magnetizes an adjacent nickel layer.
In principle, this memory device can be downscaled to the size of a single magnetic nanoparticle and might soon allow for the fabrication for high-density memory-on-a-chip devices.