Mao-Peng Miao, Nanshu Liu, Wen-Hao Zhang, Jian-Wang Zhou, Dao-Bo Wang, Cong Wang, Wei Ji, and Ying-Shuang Fu
Abstract:
Noncollinear magnetic orders in monolayer van der Waals magnets are crucial for probing delicate magnetic interactions under minimal spatial constraints and advancing miniaturized spintronic devices. Despite their significance, achieving atomic-scale identification remains challenging. In this study, we utilized spin-polarized scanning tunneling microscopy and density functional theory calculations to identify spin-spiral orders in mono- and bi-layer NiI2, grown on graphene-covered SiC(0001) substrates. We discovered two distinct spin-spiral states with Q vectors aligning and deviating by 7° from the lattice direction, exhibiting periodicities of 4.54 and 5.01 times the lattice constant, respectively. These findings contrast with bulk properties and align closely with our theoretical predictions. Surprisingly, the finite sizes of monolayers induce incommensurability with the spin-spiral period, facilitating collective spin switching behavior under magnetic fields. Our research reveals intrinsic noncollinear magnetism at the monolayer limit with unprecedented resolution, paving the way for exploring novel spin phenomena.
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