  The bistability of ordered spin states in ferromagnets (FMs) provides the
magnetic memory functionality. Traditionally, the macroscopic moment of ordered
spins in FMs is utilized to write information on magnetic media by a weak
external magnetic field, and the FM stray field is used for reading. However,
the latest generation of magnetic random access memories demonstrates a new
efficient approach in which magnetic fields are replaced by electrical means
for reading and writing. This concept may eventually leave the sensitivity of
FMs to magnetic fields as a mere weakness for retention and the FM stray fields
as a mere obstacle for high-density memory integration. In this paper we report
a room-temperature bistable antiferromagnetic (AFM) memory which produces
negligible stray fields and is inert in strong magnetic fields. We use a
resistor made of an FeRh AFM whose transition to a FM order 100 degrees above
room-temperature, allows us to magnetically set different collective directions
of Fe moments. Upon cooling to room-temperature, the AFM order sets in with the
direction the AFM moments pre-determined by the field and moment direction in
the high temperature FM state. For electrical reading, we use an
antiferromagnetic analogue of the anisotropic magnetoresistance (AMR). We
report microscopic theory modeling which confirms that this archetypical
spintronic effect discovered more than 150 years ago in FMs, can be equally
present in AFMs. Our work demonstrates the feasibility to realize
room-temperature spintronic memories with AFMs which greatly expands the
magnetic materials base for these devices and offers properties which are
unparalleled in FMs.

Materials Science