Exchange Bias in Antiferromagnetic Mn3Sn Monolayer Films

${\mathrm{Mn}}_{3}\mathrm{Sn}$ is an antiferromagnet with a noncollinear spin order, and the spin structures can be controlled by an external magnetic field. When a magnetic field is applied, ${\mathrm{Mn}}_{3}\mathrm{Sn}$ with the inverse triangular spin structure exhibits the coexistence of antiferromagnetism and weak ferromagnetism. Here we observe that both the magnetization hysteresis loops and anomalous Hall curves of ${\mathrm{Mn}}_{3}\mathrm{Sn}$ single-layer films present exchange bias after field cooling, which are generally observed in ferromagnet/antiferromagnet bilayers. A part of the antiferromagnetic spin structure of ${\mathrm{Mn}}_{3}\mathrm{Sn}$ with negligible net moments is frozen by the field-cooling process, while for the other part of ${\mathrm{Mn}}_{3}\mathrm{Sn}$, the switching of the inverse triangular spin structure with weak moments by external magnetic fields results in sizable anomalous Hall curves. The stable frozen antiferromagnetic part pins the weak moments and the inverse triangular spin structures can explain the exchange bias in magnetization hysteresis loops and anomalous Hall curves. The finding of exchange bias in antiferromagnetic ${\mathrm{Mn}}_{3}\mathrm{Sn}$ single-layer films with noncollinear spin order adds a different dimension to antiferromagnetic spintronics.