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 [3]. In an outlook, it will be demonstrated that also other iron rich phyllosilicates can serve as a platform for 2D magnetism.

LOCATION:  Institute Ruđer Bošković, 3rd wing, lecture hall

 

Seminar hosts: Neven Šantić i Damir Dominko