Atomically thin magnets are the key element to build up spintronics based on twodimensional materials. The surface nature of two-dimensional ferromagnet opens up opportunities to improve the device performance efficiently. Here, we report the intrinsic ferromagnetism in atomically thin monolayer CrBr3, directly probed by polarization resolved magnetophotoluminescence. The spontaneous magnetization persists in monolayer CrBr3 with a Curie temperature of 34 K. The development of magnons by the thermal excitation is in line with the spin-wave theory. We attribute the layer-number dependent hysteresis loops in thick layers to the 2 magnetic domain structures. As a stable monolayer material in air, CrBr3 provides a convenient platform for fundamental physics and pushes the potential applications of the two-dimensional ferromagnetism.Ferromagnetism in atomically thin magnet has been studied in a variety of van der Waals materials 1, 2 , including metallic Fe3GeTe2 3, 4 , semiconducting Cr2Ge2Te6 5 and insulating CrI3 6 .Even though the long-range magnetic order is highly suppressed by the thermal excitation of magnons in a two-dimensional (2D) magnet at finite temperature 7 , the magnetic anisotropy opens an energy gap in the magnon spectra and therefore, protects the ferromagnetism in two dimensions.The magnon-magnon interaction in such van der Waals ferromagnets also provides a platform to study the fundamental topological spin excitation, for example, Dirac magnon 8 and topological magnon surface state 9 . Moreover, in contrast to the three-dimensional ferromagnet, magnetic 2D materials show tunable magnetic properties due to their surface nature 1-3, 10-13 . Particularly the layer-number dependent 4, 6, 14 and gate-tunable magnetism 3, 10-13 opens a new way to build spintronic devices with high accuracy and efficiency 15-20 .Among various van der Waals ferromagnets, CrBr3 is an interesting platform to study the magnetism in low dimensions and light matter interactions in magnetic materials. The neutron scattering has revealed the Dirac points in bulk CrBr3 21, 22 , formed by acoustic and optical spinwave modes, where both intralayer and interlayer exchange interactions play an important role.On the other hand, optical absorption spectra in CrBr3 have shown the out-of-plane magnetic field dependence 23 , suggesting potential applications in optoelectronics. However, magnetism in atomically thin CrBr3, especially in monolayer limit, is still unknown.

No abstract

The development of intrinsic ferromagnetism in two-dimensional (2D) limit is at the core of ultra-compact spintronic applications. However, direct synthesis of non-layered 2D magnets with strong ferromagnetic order is still in infancy. Here we report the phasecontrollable synthesis of trigonal and monoclinic Cr5Te8 flakes via a facile chemical vapor deposition route. Both phases exhibit robust ferromagnetism with strong perpendicular anisotropy down to a few nanometers, as confirmed by both magneto-optical and 2 magnetotransport measurements. High Curie temperature up to 200 K is obtained by manipulating the phase structure and thickness. Remarkably, a colossal anomalous Hall effect is observed in the more distorted monoclinic Cr5Te8 with an enhanced anomalous Hall conductivity of 650 Ω -1 cm -1 and anomalous Hall angle of 5% achieved simultaneously. Our work paves the way for the scalable synthesis of 2D magnetic materials and highlights the great potential of Cr5Te8 for engineering future spintronic devices.

A phage-displayed library of variable domain of heavy chain of the heavy chain antibody (VHH) or nanobody (Nb) was constructed after immunizing an alpaca with aflatoxin B1 (AFB1) conjugated with bovine serum albumin (AFB1-BSA). Two AFB1-specific nanobodies were selected. The obtained nanobodies were compared to an aflatoxin-specific monoclonal antibody B5 with respect to stability under organic solvents and high temperature. The two nanobodies could bind antigen specifically after exposure to temperatures as high as 95 °C. Besides, the nanobodies showed better or similar tolerance to organic solvents. A competitive ELISA with nanobody Nb26 was developed for the analysis of AFB1, exhibiting an IC50 value of 0.754 ng/mL (2.4 μM), linear range from 0.117 to 5.676 ng/mL. Due to the high tolerance to methanol, sample extracts were analyzed by nanobody-based ELISA without dilution. The recovery from spiked peanut, rice, corn and feedstuff ranged from 80 to 115%. In conclusion, the isolated nanobodies are excellent candidates for immunoassay application in aflatoxin determination.