Unconventional Magnon Transport in Antiferromagnet NiPS₃ Induced by an Anisotropic Spin-Flop Transition

Nonlocal magnon transport can provide valuable insight into the magnetic properties of magnetic insulators (MIs). A spin-flop transition, a typical magnetic reorientation in antiferromagnets, is expected to affect magnon transport, but studies on this topic are still rare and remain challenging, especially for van der Waals materials. Here we demonstrate the unconventional magnon transport driven by an anisotropic spin-flop transition in the van der Waals antiferromagnet NiPS₃. Examining the nonlocal voltage from thermally driven magnons reveals sharp jumps at certain directions when an in-plane magnetic field aligns with the b-axis of NiPS₃, attributed to an in-plane anisotropic spin-flop transition. Furthermore, the thermally driven magnon signal exhibits a 1/d² decay in thin NiPS₃, evidencing that it is dominated by the intrinsic spin Seebeck effect. Our findings highlight that the electrical detection of magnon currents in a nonlocal device geometry serves as a powerful approach for studying magnetic phase transitions in MIs.