Magnetic materials have been used for storing information for more than half a century, from the first magnetic tapes to modern data servers. These technologies have in common the usage of ferromagnets, producing magnetic fields which are easily measurable. Researchers at the University of Nottingham are working with Diamond Light Source to develop new technologies based on a different class of magnetic material: an antiferromagnet, which does not produce a magnetic field, but which has a hidden magnetic order that can be used to store the ones and zeros of information.
Looking at the atomic scale, each atom is like a small magnetic compass, having a small magnetic moment. In a ferromagnet, once the information is written, all those atomic moments remain oriented in the same direction. In antiferromagnets, each magnetic moment aligns exactly opposite to its neighbours, effectively cancelling them out (Figure 1). This arrangement has some important advantages for memory applications: magnetic bits do not interact with each other, so can be packed more closely; they do not interact with external magnetic fields; their resonant frequencies, which determine the speed that information can be written, is typically 1000 times larger than in ferromagnets. Antiferromagnets can therefore be useful, but how would you store and read information in a material whose total magnetic moment is always zero? Dr Peter Wadley, a researcher at the University of Nottingham, and Sonka Reimers, a joint Nottingham and Diamond PhD student, are trying to answer that question in their search for new technologies for information storage and processing.
Figure: Schematic of magnetic moment orientation for binary information storage using (left) a ferromagnet. Full image here.