Chiral-lattice magnets can exhibit a variety of physical phenomena when time-reversal symmetry is broken by their magnetism. For example, nonreciprocal responses of (quasi)particles have been widely observed in chiral-lattice magnets with macroscopic magnetization. Meanwhile, time-reversal symmetry can also be broken in antiferromagnets without magnetization. Here we report an unconventional chirality-magnetism coupling in a chiral-lattice antiferromagnet Pb(TiO)Cu₄(PO₄)₄ whose time-reversal symmetry is broken by an ordering of magnetic quadrupoles. Our experiments demonstrate that a sign of magnetic quadrupoles is controllable by a magnetic field only, which is generally impossible in consideration of the symmetry of magnetic quadrupoles. Furthermore, we find that the sign of magnetic quadrupoles stabilized by applying a magnetic field is reversed by a switching of the chirality. Our theoretical calculations and phenomenological approach reveal that this unusual coupling between the chirality and magnetic quadrupoles is mediated by the previously-unrecognized magnetic octupoles that emerge due to the chirality.

当时间反转对称性被其磁性破坏时，手性晶格磁铁可以表现出多种物理现象。例如，在具有宏观磁化强度的手性晶格磁铁中广泛观察到（准）粒子的非互易响应。同时，在没有磁化的反铁磁体中，时间反转对称性也可以被破坏。在这里，我们报告了手性-晶格反铁磁体 Pb(TiO)Cu ₄ (PO ₄ ) _{4 中}的非常规手性-磁性耦合其时间反转对称性被磁性四极子的排序破坏。我们的实验表明，磁四极杆的符号只能由磁场控制，考虑到磁四极杆的对称性，这通常是不可能的。此外，我们发现通过施加磁场稳定的磁性四极杆的符号通过手性的切换而反转。我们的理论计算和现象学方法表明，手性和磁性四极杆之间的这种不寻常的耦合是由以前无法识别的由于手性而出现的磁性八极子介导的。