Octupole-driven spin torque switching of antiferromagnetic tunnel junctions

Magnetic tunnel junctions based on ferromagnets are canonical devices in spintronics, with wide-ranging applications in data storage, computing and sensing. They simultaneously exhibit mechanisms for electrical detection and control of magnetic order through the tunnelling magnetoresistance (TMR)^1-5 and spin-transfer torque^6-9 effects, respectively. It was long assumed that neither of these effects could be sizeable in all-antiferromagnetic tunnel junctions (AATJs), considering that they have no net magnetization. However, it was recently shown that AATJs based on chiral antiferromagnets do exhibit TMR due to their non-relativistic momentum-dependent spin polarization and cluster magnetic octupole moment, which are manifestations of their spin-split band structure^10-13. However, the reciprocal effect, that is, the antiferromagnetic counterpart of spin-transfer torque, has been assumed non-existent due to the total electric current being spin-neutral. Here we report nanoscale AATJs that display this reciprocal effect, which we term octupole-driven spin-transfer torque (OTT). We demonstrate current-induced OTT switching of PtMn₃|MgO|PtMn₃ AATJs, with a TMR value of 363% at room temperature and switching current densities of the order of 10 MA cm^-2. Our theoretical modelling explains the origin of OTT in terms of the imbalance between intra- and inter-sublattice spin currents across the AATJ, and, equivalently, in terms of the non-zero net cluster octupole polarization of each PtMn₃ layer. This work establishes a new materials platform for antiferromagnetic spintronics and provides a pathway towards deeply scaled magnetic memory and room-temperature terahertz technologies.