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.

Ordered mesoscale structures in 2D materials induced by small misorientations have allowed for a wide variety of electronic, ferroelectric, and quantum phenomena to be explored. Until now, the only mechanism to induce this periodic ordering was via mechanical rotations between the layers, with the periodicity of the resulting moiré pattern being directly related to twist angle. Here we report a fundamentally distinct mechanism for emergence of mesoscopic periodic patterns in multilayer sulfur-containing metal phosphorus trichalcogenide, MnPS3, induced by the electron beam. The formation under the beam of periodic hexagonal patterns with several characteristic length scales, nucleation and transitions between the phases, and local dynamics are demonstrated. The associated mechanisms are attributed to the relative contraction of the layers caused by beam-induced sulfur vacancy formation with subsequent ordering and lattice parameter change. As a result, the plasmonic response of the system is locally altered, suggesting an element of control over plasmon resonances by electron beam patterning. We pose that harnessing this phenomenon provides both insight into fundamental physics of quantum materials and enables device applications by enabling controlled periodic potentials on the atomic scale.

Second-harmonic generation has been applied to study lattice, electronic, and magnetic proprieties in atomically thin materials. However, inversion symmetry breaking is usually required for the materials to generate a large signal. In this work, we report a giant second-harmonic generation that arises below the Neél temperature in few-layer centrosymmetric FePS 3 . A layer-dependent study indicates the detected signal is from the second-order nonlinearity of the surface. The magnetism-induced surface secondharmonic response is 2 orders of magnitude larger than those reported in other magnetic systems, with the surface nonlinear susceptibility reaching 0.08−0.13 nm 2 /V in 2−5 L samples. By combing linear dichroism and second-harmonic generation experiments, we further confirm the giant second-harmonic generation is coupled to nematic orders formed by the three possible Zigzag antiferromagnetic domains. Our study shows that the surface secondharmonic generation is also a sensitive tool to study antiferromagnetic states in centrosymmetric atomically thin materials.

Nowadays, one-phase and full-color phosphors have gained increasing interest. Here, we show that Mn-activated zinc gallogermanate, Zn 1+x Ga 2-2x Ge x O 4 : Mn, x = 0 ~1, phosphors exhibit a broadly tunable luminescence from green to deep red with the substitution of Ga 3+ by Ge 4+ . The green and deep red emissions are attributed to Mn 2+ and Mn 4+ occupying the tetrahedrally coordinated Zn 2+ and octahedrally coordinated Ga 3+ sites, respectively. The origin of the tunable luminescence is discussed. The present phosphors have potential uses in field emission displays and in vivo bio-imaging. The in vivo activation of persistent nanophosphors for optical imaging of vascularization, tumours and grafted cells," Nat.

In this study, the Indium (In) doped Cd1–xMnx Te (xMn=0.1, CdMnTe) crystals with excess Te in the amount of 0 and 1.2 at% were grown by the Bridgman method. The segregation coefficient of In dopants distributions in the CdMnTe crystals with and without excess Te were determined to be 0.08 and 0.11, respectively. The IR transmission microscopy shown that the size of Te inclusions in CdMnTe crystal with excess Te increased to 5–13 μm with the concentrations of (2–3)×105 cm–3. The PL spectra indicated the formation of Te antisite donor and the compensation of Cd vacancies by Te antisites. The Current‐Voltage measurements were performed and the resistivity of the CdMnTe crystal with excess Te was in the range of 108–109 Ω·cm, increased by one order as compared to the crystal without excess Te. Under the radiation of 59.5 keV 241Am, The CdMnTe planar detectors fabricated from the crystal with excess Te revealed the energy resolution of 8.4%, however, no energy response is resolved in the CdMnTe detectors without excess Te. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)