Institut für Physik, Montanuniversität Leoben, A-8700 Leoben, Austria
07/07/2022/ at 11:00h
IRB 3rd wing, lecture hall
Since the first reports on intrinsically magnetic two-dimensional (2D) materials in 2017 [1,2], the price-to-pay for accessing their monolayers is still the lack of ambient stability.
We discovered in a mineral aggregate – mainly composed of hematite, magnetite, and chalcopyrite – soft layers of which macroscopic flakes easily could be peeled off that stuck to a permanent magnet. Employing mechanical exfoliation, we succeeded in thinning and transferring micrometer sized – mainly hexagonally shaped – flakes to SiO2 substrates. Energy dispersive x-ray spectroscopy (EDS) revealed magnesium and silica as major components of the flakes. Raman spectroscopy indicated the presence of hydroxide groups, pointing towards talc, a hydrated magnesium phyllosilicate mineral, namely talc (Mg3Si4O10(OH)2). Long-term EDS and Raman spectroscopy revealed that in the flakes about 10 % of the Mg atoms are substituted by Fe which clusters into about 20 nm regions according to scanning transmission electron microscopy (STEM). With atomic force microscopy, a minimum flake thickness of 1 nm was determined indicating cleavage down to a talc monolayer. Combined magnetic force microscopy (MFM) measurements in external out-of-plane fields up to 0.5 T and SQUID magnetometry measurements imply that the 2D Fe-rich talc exhibits weak ferromagnetic behavior. The flakes are also showing long-term stability under ambient conditions in contrast to the 2D magnets reported so far . In an outlook, it will be demonstrated that also other iron rich phyllosilicates can serve as a platform for 2D magnetism.
 B. Huang, et al., Nature 546, 270 (2017).
 A. Matković, et al., npj 2D Mat. Appl. 5, 94 (2021).
Work is supported by FWF, Austria via 2020 START program (grant # Y1298 N) and has been performed in collaboration with A. Matković, M. Z. Khan, K.-P. Gradwohl, M. Kratzer O. E. Peil, C. Gammer, R. Bakker, J. Raith (all Leoben), E. Fisslthaler, D. Knez, F. Hofer (all Graz), and A. Sharma, D.R.T. Zahn, G. Salvan (all Chemnitz).