This paper investigates the unconventional chirality-magnetism coupling in the chiral-lattice antiferromagnet Pb(TiO)6Cu4(PO4)4, where time-reversal symmetry is broken by magnetic quadrupole ordering. Experiments show that the magnetic quadrupole sign is controlled solely by a magnetic field, a phenomenon generally impossible considering the symmetry of magnetic quadrupoles. The sign of the magnetic quadrupoles is reversed by chirality switching. Theoretical calculations and a phenomenological approach reveal that this coupling is mediated by magnetic octupoles emerging due to chirality.
