Origin of two-dimensional MXene/ferromagnetic interface evaluated by angle-dependent hard X-ray photoemission spectroscopy.

Emergent ferromagnetism on the surface of two-dimensional (2D) MXene is investigated by X-ray magnetic circular dichroism (XMCD) and angle-dependent hard X-ray photoemission spectroscopy (HAXPES). Focusing on CrN as one of the 2D-MXenes, high quality bilayers of CrN/Co and CrN/Pt are prepared by a magnetron sputtering technique. XMCD reveals the induced magnetic moment of Cr in the CrN/Co interface, while it is not observed in the CrN/Pt interface at room temperature. In order to distinguish the possible origins of either the interlayer magnetic exchange coupling or the charge transfer model as the source of ferromagnetism at the interface, the additional controlled CrN/Cu bilayer, whose work function of Cu is consistent with Co, is prepared. HAXPES spectra for the Cr 2 core level near the interface of CrN/Cu are consistent with that of CrN/Co, indicating that the induced magnetic moment of Cr observed by XMCD for CrN/Co can be attributed to the model of interlayer magnetic exchange coupling, rather than the charge transfer model, leading to emergent ferromagnetism at the interface with 2D-MXene.