Semiconductor transistors, which are the founding blocks of modern information processing technologies, allow for the control of the electrical current by electrostatic gating, light, or temperature. Metal ferromagnets like iron, used in information storage devices, allow for a complementary approach in which the electrical current is controlled by manipulating the orientation of the elementary magnets carried by electrons, the so-called electron spins.
For more than a decade, the research towards merging the semiconducting and magnetic approaches to microelectronics in one material has focused on utilizing artificial ferromagnetic semiconductor materials, e.g. GaMnAs. These are, however, difficult to synthesize and so far have not met the requirements on material properties practical for microelectronic applications.
Researchers from the Institute of Physics of the Academy of Sciences of the Czech Republic, in collaboration with researchers from Barcelona, Berkeley, and Halle have demonstrated an experimental spin-based microelectronic device using an antiferromagnetic semiconductor compound Sr2IrO4. The work entitled “Anisotropic magnetoresistance in an antiferromagnetic semiconductor” has been published in Nature Communications (DOI: 10.1038/ncomms5671; 10th September 2014).
Compared to ferromagnets, antiferromagnets have been largely overlooked in the microelectronic research and applications. These materials are magnetic inside, however, their microscopic magnets sitting on individual atoms alternate between two opposite orientations. The antiparallel spin configuration in antiferromagnets, instead of the parallel configuration in ferromagnets, makes the magnetism in antiferromagnets invisible on the outside. This “hidden” magnetic order in antiferromagnets may have, however, important advantages over ferromagnets. It implies that if information was stored in an antiferromagnetic memory it would be insensitive to disturbing external magnetic fields and an antiferromagnetic bit would also not affect the neighboring antiferromagnetic bit no matter how densely the bits were arranged in the memory. Moreover, spins in antiferromagnets can be reoriented, and therefore the information written, hundreds to thousands times faster than in ferromagnets. And, finally, antiferromagnetic semiconductors are much more abundant than ferromagnetic semiconductors, and many of them have naturally the favourable properties required for microelectronics.
Experiments in the Sr2IrO4 device demonstrated that the electrical current flow through the device can be controlled by the usual means provided by conventional semiconductors like silicon but, simultaneously, also by reorienting the electron spins in this antiferromagnet. “Our findings open a route to integrate semiconducting and spin-based microelectronics by utilizing antiferromagnets”, says Xavi Marti from the Institute of Physics.
For detail information contact Xavi Marti or Tomáš Jungwirth from the Institute of Physics ASCR, Cukrovarnická 10, 162 53 Praha 6, e-mail: xmartifzu [dot] cz or jungwfzu [dot] cz