Octupole-driven magnetoresistance in an antiferromagnetic tunnel junction

The tunnelling electric current passing through a magnetic tunnel junction (MTJ) is strongly dependent on the relative orientation of magnetizations in ferromagnetic electrodes sandwiching an insulating barrier, rendering efficient readout of spintronics devices(1-5). Thus, tunnelling magnetoresistance (TMR) is considered to be proportional to spin polarization at the interface(1) and, to date, has been studied primarily in ferromagnets. Here we report observation of TMR in an all-antiferromagnetic tunnel junction consisting of Mn3Sn/MgO/Mn3Sn (ref. (6)). We measured a TMR ratio of around 2% at room temperature, which arises between the parallel and antiparallel configurations of the cluster magnetic octupoles in the chiral antiferromagnetic state. Moreover, we carried out measurements using a Fe/MgO/Mn3Sn MTJ and show that the sign and direction of anisotropic longitudinal spin-polarized current in the antiferromagnet(7) can be controlled by octupole direction. Strikingly, the TMR ratio (about 2%) of the all-antiferromagnetic MTJ is much larger than that estimated using the observed spin polarization. Theoretically, we found that the chiral antiferromagnetic MTJ may produce a substantially large TMR ratio as a result of the time-reversal, symmetry-breaking polarization characteristic of cluster magnetic octupoles. Our work lays the foundation for the development of ultrafast and efficient spintronic devices using antiferromagnets(8-10).

Automated summary

The tunnelling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) is usually studied in ferromagnetic materials, but this study reports the observation of TMR in an all-antiferromagnetic tunnel junction. A TMR ratio of about 2% was measured at room temperature, which is attributed to the configuration of cluster magnetic octupoles in the chiral antiferromagnetic state. Sign and direction of anisotropic longitudinal spin-polarized current in the antiferromagnet can be controlled by octupole direction. Theoretical analysis suggests that the chiral antiferromagnetic MTJ can produce a substantially large TMR ratio due to the time-reversal, symmetry-breaking polarization characteristic of cluster magnetic octupoles.