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 Cr₂N as one of the 2D-MXenes, high quality bilayers of Cr₂N/Co and Cr₂N/Pt are prepared by a magnetron sputtering technique. XMCD reveals the induced magnetic moment of Cr in the Cr₂N/Co interface, while it is not observed in the Cr₂N/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 Cr₂N/Cu bilayer, whose work function of Cu is consistent with Co, is prepared. HAXPES spectra for the Cr 2<i>p</i> core level near the interface of Cr₂N/Cu are consistent with that of Cr₂N/Co, indicating that the induced magnetic moment of Cr observed by XMCD for Cr₂N/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. Induced magnetic moment is found on the surface of 2D-MXene by XMCD, and angle-dependent HAXPES analysis is used to show that it is not due to charge-transfer but can be attributed to the exchange magnetic coupling with the adjacent ferromagnetic layer.