Importance of Paramagnetic Background Subtraction for Determining the Magnetic Moment in Epitaxially Grown Ultrathin van der Waals Magnets

Due to the atomically thin nature of monolayer and few-layer van der Waals magnets, the undesired background signal from the substrate can have significant contribution when characterizing their magnetic properties. This brings challenges in accurately determining the magnitude of the magnetic moment of the epitaxially grown van der Waals magnets on bulk substrates. We discuss the impact of the background subtraction method for accurately determining the magnetic moments in such systems. Using the recently reported intrinsic two-dimensional van der Waals ferromagnet MnSe2 as an example, we show that a normal diamagnetic background subtraction method in analyzing the bulk magnetometry measurement will result in an unexpectedly large magnetic moment (greater than ~10 μB per formula unit). Through our systematic growth study, we identify an additional paramagnetic signal due to unintentional Mn doping of the substrate. To extract the correct magnetic moment, a paramagnetic background should also be considered. This yields a total magnetic moment of ~4 μB per formula unit in monolayer MnSe2, which is in close agreement to the theoretically predicted value.