Researchers from the Institute of Physics introduce antiferromagnetic memories
In ferromagnetic materials, information can be stored in “zeros” and “ones” defined by the orientation of magnetic moments, which can be pictured as small compasses (see Fig. 1a). This technology is behind a range of memory applications from kilobyte magnetic stripe cards to terabyte computer hard disks. It is dangerous to place a parking ticket or a hard disk next to another magnet or device generating strong magnetic fields because the magnetic moments of the memory can be unintentionally reoriented and the information lost (see Fig. 1b).
Moreover, being magnetic on outside, a ferromagnetic bit could disturb the neighboring one if
the integration of bits in high-density memories was pushed to limits.
Researchers from the Institute of Physics of the Academy of Sciences of the Czech Republic, in
collaboration with researchers from Berkeley and Barcelona, have demonstrated that it is possible
to use another type of magnetic materials, the so-called antiferromagnets to store information. The
work entitled “Room-temperature antiferromagnetic memory resistor” has been published in
Nature Materials (DOI: 10.1038/NMAT3861; 26th January 2014).
Antiferromagnetic materials are magnetic inside, however, their microscopic magnetic moments
sitting on individual atoms alternate between two opposite orientations (see Fig. 1c). This
antiparallel moment configuration in antiferromagnets, instead of the parallel configuration in
ferromagnets, makes the magnetism in antiferromagnets invisible on the outside. It implies that if
information was stored in an antiferromagnetic memory it would be insensitive to disturbing
external magnetic fields (see Fig. 1d), and an antiferromagnetic bit would also not affect the
neighboring antiferromagnetic bit no matter how densely the bits were arranged in the memory. The
outstanding question, however, is how to read and write information on an antiferromagnetic
bit.
The answer is provided in the above
Nature Materials articleby using a special antiferromagnet which changes to a ferromagnet
upon heating. To be able to select the magnetic moment direction of the antiferromagnet for
encoding “zeros” or “ones” (see Fig. 1c), it is heated up to bring the material into the
ferromagnetic phase. A magnetic field pointing along one or another direction is then applied and
the material is allowed to cool down back into the antiferromagnetic state where the direction of
the antiparallel moments “freezes” (Fig. 1c) along the magnetic field direction applied during
cooling. Once in the antiferromagnetic state, the information is written and is no more sensitive
to external magnetic fields. Information is subsequently read by simply measuring the electrical
resistance which depends on the relative angle between the measuring current run through the
antiferromagnetic bit and the direction of the antiparallel magnetic moments in the bit (see Fig.
1c). “We have introduced a new class of materials that can be used for constructing more robust
magnetic memories”, says Xavi Marti from the Institute of Physics.
For detail information contact Xavi Marti or Tomáš Jungwirth from the Institute of Physics ASCR,
v.v.i., Cukrovarnická 10, 162 53 Praha 6, e-mail: xmarti@fzu.cz or
jungw@fzu.cz
3 Feb 2014
