International research team demonstrates electrical switching of an antiferromagnet Ferromagnets and antiferromagnets are the two common forms of magnetically ordered materials. Traditionally we thought that magnetism can be easily controlled and utilized only in ferromagnets. Researchers from the Czech Republic, United Kingdom, and Germany change this perception by demonstrating electrical switching of magnetization in an antiferromagnetic microchip.
The work was published online by the journal Science on 14 January 2016 (DOI: 10.1126/science.aab1031).
In ferromagnetic materials, all microscopic magnets sitting on individual atoms have their north poles pointing in the same direction by which they add up into a macroscopic magnet. Without physically rotating the magnet, the direction of the north pole can be reversibly switched by running an electrical current through a nearby electromagnetic wire in one or the other direction. This is the principle of data recording and storage in ferromagnetic media.
Antiferromagnets have the north poles of half of the microscopic atomic magnets pointing in one direction and the other half in the opposite direction. Reversing the magnetization in an antiferromagnet thus requires two sets of electromagnets with opposite currents. Realizing this is unfeasible because the number of atoms in a magnetic bit is large and atoms with oppositely oriented microscopic magnets are completely mixed in the antiferromagnetic crystal with their distances typically not exceeding 10-9 meters.
Instead of the science-fiction scenario of attaching a separate electromagnetic wire next to each individual atom, members of the team have proposed a year ago a new physical phenomenon. The explanation of its origin would require a tour to the realm of relativistic quantum physics but its implication can be pictured in a remarkably straightforward way. When driving a macroscopic electrical current through certain antiferromagnetic crystals, virtual microscopic electromagnets form spontaneously at individual atomic sites and act in the precisely opposite way on atoms with oppositely oriented microscopic magnets. When the electrical current is switched off, these virtual micro-electromagnets disappear. This provides practical means for writing and storing data in an antiferromagnet (see Figure).
The research team has picked CuMnAs as one of the suitable candidate antiferromagnets for demonstrating the electrical switching, and fabricated experimental memory microchips from this material. They observe reversible electrical switching, combined with electrical readout, at room temperature and with writing currents comparably low to those used in commercial ferromagnetic memories.
“In contrast to ferromagnets, information stored by antiferromagnetic materials cannot be accidentally wiped even by large magnetic fields. Moreover, antiferromagnetic materials do not produce a stray magnetic field, eliminating the possibility of unintentional magnetic ‘cross-talk’ between neighbouring memory elements, and also of secure data being stolen by using common magnetic scanners. We have already demonstrated these favourable characteristics of antiferromagnets for digital data storage in our present work. Another foreseen advantage yet to be established is the speed by which information can be written in antiferromagnetic memories. Its physical limit is 100-1000 times higher than in ferromagnets,” says Tomas Jungwirth from the Czech Academy of Sciences.
Original publication:
Electrical switching of an antiferromagnet,
P. Wadley et al., Science published online 14 January (2016), DOI: 10.1126/science.aab1031