Direct Imaging of Antiferromagnetic Domains and Anomalous Layer-Dependent Mirror Symmetry Breaking in Atomically Thin MnPS3

Abstract

We have developed a sensitive cryogenic second-harmonic generation microscopy to study a van der Waals antiferromagnet MnPS3. We find that long-range Néel antiferromagnetic order develops from the bulk crystal down to the bilayer, while it is absent in the monolayer. Before entering the long-range antiferromagnetic ordered phase in all samples, an upturn of the second harmonic generation below 200 K indicates the formation of the short-range order and magneto-elastic coupling. We also directly image the two antiphase (180 • ) antiferromagnetic domains and thermally-induced domain switching down to bilayer. An anomalous mirror symmetry breaking shows up in samples thinner than ten layers for the temperature both above and below the Néel temperature, which indicates a structural change in few-layer samples. Minimal change of the second harmonic generation polar patterns in strain tuning experiments indicate that the symmetry crossover at ten layers is most likely an intrinsic property of MnPS3 instead of an extrinsic origin of substrate-induced strain. Our results show that second harmonic generation microscopy is a direct tool for studying antiferromagnetic domains in atomically thin materials, and opens a new way to study two-dimensional antiferromagnets.

Universal three-state nematicity and magneto-optical Kerr effect in the charge density waves in AV$_3$Sb$_5$ (A=Cs, Rb, K)

“…We also do not see any change across the T CDW . Our observation of AV 3 Sb 5 being centrosymmetric agrees with previous studies [30,49], and our detection sensitivity is much higher [58,59]. Interestingly, in the CsV 3 Sb 5 , within the same birefrigence domain as shown in Extended Fig.…”

Observation of giant surface second harmonic generation coupled to nematic orders in the van der Waals antiferromagnet FePS$_3$

“…E i (ω) is the electric field from the fundamental light, and d is the sample thickness. Note that the SHG signal scales with the effective thickness as reported in the previous research [32].…”

“…1(b)). According to the previous studies, in the Néel-type antiferromagnet MnPS 3 , an electric-dipole SHG signal induced by the magnetism is observed down to bilayer samples [12,32]. It is usually believed that, however, the second-harmonic response is insensitive to the Zigzag-type antiferromagnetic orders because of the preserved inversion symmetry [12].…”

“…1(d) show the temperature dependence of SHG intensity of a 3 L and a 12 L MnPS 3 flake. A sudden rise of SHG intensity below the Néel temperature of 78 K is observed, because the Néel-type antiferromagnetism breaks the inversion symmetry in this system [12,32]. The SHG response is believed to have two parts, including the electric-dipole term and the electric-quadruple term:…”

Limited Ferromagnetic Interactions in Monolayers of MPS3 (M = Mn and Ni)

“… 72 In the case of MnPS 3 , the magnetic order has been presented down to the bilayer and was reported to be absent in the monolayer. 74 The suppression of the Néel temperature in thin samples can be associated with reducing the interplanar coupling in atomically thin samples. 3 , 72 Aforementioned results demonstrate that the magnetic ordering in monolayers of MPX 3 is still under a hot debate and many experiments are being carried out to verify the theoretical predictions.…”