Transition Metal-Doped Boron Nitride Atomic Sheets with an Engineered Bandgap and Magnetization

Abstract

Controlled doping of flat atomic sheets of boron nitride (BN) can in principle break charge and spin symmetries. In contrast to graphene that oxidizes at >500 °C, due to its high melting point (ca. 2700 K) and the electrically insulating nature (Eg ∼ 5.5 eV), BN presents strong material candidature for flexible magnetic memory chips that are functional even under fire. Here, we report the transition metal (Fe and Cr) doping of BN by microwave and solvothermal methods. X-ray photoelectron spectroscopy reveals ∼17% doping by microwave (800 W) and <11% doping by the solvothermal method. Cr or Fe doping brings the bandgap down to ∼3.6 or ∼2.0 eV, respectively, for the doped BN samples. Cr doping by microwave results in intrinsic ferromagnetic ordering evident from the high Curie point (∼380 K) in contrast to orbital-mediated magnetic ordering in solvothermal Cr-doped BN systems. Fe doping raises magnetization values in particular. Spin-polarized DFT band structure calculations suggest vivid spin asymmetry caused by doping, supporting our experimental findings on doped BN samples.