We present a theory for the relaxation time of the octupole order parameter in nanoscale chiral antiferromagnets (AFMs) coupled to thermal baths and spin injection sources. Using stochastic spin dynamics simulations, we demonstrate that the octupole moment relaxes through two distinct mechanisms—escape over a barrier and precessional dephasing—as the barrier for octupole fluctuations is lowered relative to the thermal energy. Notably, the octupole moment relaxes orders of magnitude faster than the typical dipolar order parameters, reaching picosecond timescales. By combining Langer’s theory with an effective low-energy description of octupole dynamics in chiral AFMs, we derive analytical expressions for the relaxation times. We find that relaxation in chiral AFMs parallels dipole relaxation in $XY$ magnets, with exchange fields serving the role of the dipole fields. Further, by drawing on the analogy between order parameter dynamics in $XY$ magnets under spin injection and current-biased Josephson junctions, we propose a new scheme for electrically tuning the octupole relaxation times. Our Letter offers fundamental insights for the development of next-generation spintronic devices that harness octupole order parameters for information encoding.

Close

PrevNext

View figure in article

• Kinetic theory
• Magnetization dynamics
• Probabilistic computing
• Spin relaxation
• Chiral magnets
• Perturbation theory