Magnetic van der Waals (vdW) materials, including ferromagnets (FM) and antiferromagnets (AFM), have given access to the investigation of magnetism in two-dimensional (2D) limit and attracted broad interests recently. However, most of them are semiconducting or insulating and the vdW itinerant magnets, especially vdW itinerant AFM, are very rare. Here, we studied the anomalous Hall effect of a vdW itinerant magnet Fe5GeTe2 (F5GT) with various thicknesses down to 6.8 nm (two unit cells). Despite the robust ferromagnetic ground state in thin-layer F5GT, however, we show that the electron doping implemented by a protonic gate can eventually induce a magnetic phase transition from FM to AFM. Realization of an antiferromagnetic phase in F5GT highlights its promising applications in high-temperature antiferromagnetic vdW devices and heterostructures.
Superparamagnetic nanoparticles with superhigh T2 relaxivity and cellular uptake are strongly desired for ultrasensitive magnetic resonance imaging (MRI). Towards this end, highly monodispersed manganese ferrite nanoparticles (MNPs, 6 nm) with mPEG‐g‐PEI and PEG coatings as model system are employed in this study to investigate the coating engineering for simultaneously high T2 relaxivity and cellular uptake. The quantitative evaluations of the intracellular uptake indicate that mPEG‐g‐PEI modified MNPs possess highly efficient cellular uptake, 2.4‐fold larger than that with mPEG coating. More significantly, this coating simultaneously leads to a remarkably high T2 relaxivity up to 331.8 mm−1 s−1, which is 4 times larger than that of the mPEG control and the largest value reported for superparamagnetic iron oxides with similar size. Modeling analysis reveals that the superior relaxivity is mainly attributed to the largely reduced diffusivity of water molecules trapped in the mPEG‐g‐PEI net. Further MRI of MDA‐MB‐231 breast cancer cells loaded MNPs with mPEG‐g‐PEI coating demonstrated the strong MR contrast in vitro effect with a T2 relaxivity as high as 92.6 mm−1 s−1, 2.5‐folds larger than reported 10 nm MNPs. This study provides a universal strategy of coating engineering of various magnetic nanoparticles for highly sensitive MRI.
Using first-principles calculations, the structural and electronic properties of monolayer SnO doped with 3d transition metals from V to Ni were investigated. The results indicate that the substitutional doping is preferred under oxygen-rich conditions for all transition metals. In addition, all dopants induce magnetism by forming TMsub except for Ni. Such a magnetic behavior is due to the interaction between the dopants and the surrounding Sn/O atoms. The stability and the origin of magnetism are investigated by considering different defect complexes. The results show that a defect complex composed of substitutional dopants and oxygen vacancies has the same magnetic moment as that of substitutional dopants of TMsub alone, whereas the magnetic moments of defect complexes composed of ubsubstitutional, TMsub, and tin vacancy, VSn, vary significantly. The moments of defect complexes, such as (Cosub + VSn) and (Nisub + VSn), are enhanced compared to those of the substitutional alone. On the other hand, the magnetic moments of (Fesub + VSn) and (Mnsub + VSn) are the same as those of substitutional dopants alone, whereas (Crsub + VSn) and (Vsub + VSn) have lower magnetic moments than single TMsub.
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