Antiferromagnetic materials, contrary to ferromagnets such as iron, are not influenced by external magnetic fields. Researchers from Great Britain, the Czech Republic, Germany and Poland show how they could still be used to store data more reliably than using ferromagnetic materials. They succeeded for the first time in electrically controlling the switching and read-out of the magnetic moment of an antiferromagnetic material. Their research work will be published online by the journal Science on 14 January 2016 (DOI: 10.1126/science.aab1031).
Ferromagnets react to external #magnetic fields by reorienting their atomic magnetic moments, or, the so-called spins. For magnetic strips on credit cards or hard drives on computers, this effect is useful on the one hand, as it allows #data to be written. On the other hand, it is necessary to shield these #materials from unwanted magnetic fields, generated for instance by certain kinds of medical equipment, so that data is not deleted by mistake.
In antiferromagnets, half of the spins point in one direction, while the other half point in the opposite direction, in a kind of chessboard pattern. The antiferromagnetic materials are therefore not influenced by magnetic fields, and are of no use in magnetic data writing methods commonly utilized today. Until now, it has only been possible for them to be used in the field of information technology in combination with other classes of materials. However, due to the fact that antiferromagnets are magnetically more robust and can in principle be switched much #faster than ferromagnets, the scientists from Forschungszentrum Jülich and their European partners looked for a way to develop them into an independent data storage material class.
Using samples made from copper manganese arsenide, they were able to #demonstrate that the alignment of the magnetic moments of certain types of antiferromagnets could be controlled with electrical pulses. “The electric current brings about a quantum mechanical torque on individual spins and allows each of them to tilt 90 degrees”, reported Dr. Frank Freimuth of the Peter Grünberg Institute and the Institute for Advanced Simulation in Jülich.
Simulation software developed in Jülich helped the theoretical physicist and his colleagues understand in detail just how the switching occurs. Importantly, the electric current must flow parallel to the original direction of the spin. To switch the spins back, a current flowing perpendicular to the first electric pulse is needed. To read out the various states of the magnet, the #researchers took advantage of the fact that the electrical resistance of the material depends on the spin direction.
“The speed with which the spins change direction depends on a material-specific interaction of the spins amongst themselves, the so-called exchange interaction, which stabilises the spin alignment. Switching can therefore take place ten times faster in antiferromagnets than in ferromagnets”, explained Freimuth’s co-worker Prof. Yuriy Mokrousov, leader of the “Topological Nanoelectronics Group” in the same institute, pointing out an advantage of the method.
Additionally, a #device that is switched electrically can be miniaturized more efficiently than one requiring a magnetic field to operate, as smaller storage areas can be manipulated by currents. Moreover, there is a wide spectrum of different materials that are antiferromagnetic at room temperature, which is essential for practical use. Antiferromagnetism is far more common than ferromagnetism and is found, for example, in metals, semiconductors and insulators, which simplifies its integration in existing concepts.