New spin torque effect switches antiferromagnetic memory devices

Researchers have demonstrated a way to electrically switch the magnetic state of nanoscale antiferromagnetic tunnel junctions at room temperature. The finding, reported in Nature, establishes a mechanism called octupole-driven spin-transfer torque, or OTT, that could help make these materials useful for magnetic memory.

The devices combine two layers of platinum manganese, PtMn3, separated by a magnesium oxide insulating barrier. The researchers report tunnelling magnetoresistance of 363% at room temperature, alongside switching current densities on the order of 10 million amperes per square centimetre.

Together, those measurements establish complementary capabilities: distinguishing magnetic states electrically and using current to change them. Resistance provides the readout signal, while the newly identified torque supplies a way to write information into the antiferromagnetic junction.

Conventional magnetic tunnel junctions rely on ferromagnets and already underpin applications in storage, computing and sensing. Their electrical readout and switching mechanisms were long considered difficult to reproduce at substantial strength in devices made entirely from antiferromagnets, which have no net magnetization.

Earlier research had shown that tunnel junctions using chiral antiferromagnets could produce a measurable resistance contrast between magnetic configurations. Their electronic structure supports spin polarization that depends on electron momentum, even without an overall magnetization. The remaining question was whether a corresponding current-driven switching effect could also exist.

The new work demonstrates that counterpart despite the total electrical current being spin-neutral. The researchers’ theoretical model attributes the torque to unequal spin currents flowing within and between magnetic sublattices. They also describe the mechanism through the cluster magnetic octupole polarization of each platinum manganese layer, which captures its more complex spin arrangement.

A team led by Northwestern Engineering’s Pedram Khalili carried out the research. In the university’s account, the significance extends beyond another switching technique: the work broadens how researchers understand interactions between electrical current and magnetic order when a material has no net magnetic dipole.

Antiferromagnets are attractive for memory partly because their cancelling spin arrangements make them less vulnerable to interference from external magnetic fields. Combining electrical writing and reading in nanoscale junctions could therefore support compact, more field-resistant information storage. Those potential advantages do not by themselves establish a commercially ready memory technology.

The researchers also see opportunities beyond storage because antiferromagnetic dynamics can reach terahertz frequencies, above the gigahertz range typical of ferromagnets. However, the reported work does not demonstrate terahertz operation. It instead provides a possible means of electrically accessing those dynamics in future devices.

According to Northwestern, the team plans to test other noncollinear antiferromagnetic materials for stronger effects and investigate direct access to terahertz dynamics. Integrating the junctions with conventional semiconductor electronics is another prospective direction, with practical memory and high-frequency applications remaining goals for further research.