Observation of ferromagnetism in black phosphorus nanosheets with high magnetization by liquid exfoliation

The Black Phosphorus (BP) nanosheets were prepared by liquid ultrasonic exfoliating the grinded layered BP bulk in organic solutions under protecting atmosphere. The samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as selective electron diffraction (SED). The possible magnetic (Fe, Co, Ni) impurities in the BP material were analyzed by an inductively coupled plasma-atomic emission spectrometry (ICP-AES). Magnetization measurements were performed using a vibrating sample magnetometer (VSM, Quantum Design PPMS-9T). The results indicate that the BP nanosheets sample has a weak ferromagnetic ordering with high magnetization 1.83 emu/g at room temperature. Analysis states the ferromagnetism is intrinsic to the BP samples, ruling out extrinsic ferromagnetism arising from magnetic metal impurities. The combination effects of magnetic moments resulting from defects or vacancies, the formation of edge states and the p orbital spin polarization of the oxygen and phosphorus atoms of the surface PO bonds contribute to the observed ferromagnetism in BP nanosheets sample. The conversion of ferromagnetism of 2D material BP at room temperature will be of great implication for spintronics application in the future.