Iron-rich talc as air-stable platform for magnetic two-dimensional materials

Abstract

Intrinsically magnetic layered materials – especially monolayers – suffer from the lack of ambient stability and mostly exhibit magnetic ordering only at cryogenic temperatures. These restrains impose a great challenge for the integration of two-dimensional magnetic materials into future technologies. We propose to overcome this by exploiting phyllosilicates, such as iron-rich talc. Via combined magnetic force microscopy in applied external magnetic fields, superconducting quantum interference device magnetometry, first-principle calculations, and structural analysis, we demonstrate that incorporated iron ions in talc are in a very robust high spin state, resulting in a weak ferromagnetic behavior at room temperature. Iron-rich talc can be thinned down to a monolayer, remaining fully stable under ambient conditions, and retaining magnetic properties even in monolayers. Finally, we propose iron-rich end members of the phyllosilicates as very promising platforms for air-stable magnetic monolayers.

Raman and Far-Infrared Synchrotron Nanospectroscopy of Layered Crystalline Talc: Vibrational Properties, Interlayer Coupling, and Symmetry Crossover

“…The Raman peaks at 194.5, 362.1, 676.2, and 1050.5 cm –1 are ascribed to the fundamental vibrations of silicates in talc, and the peak at 3678.8 cm –1 is the characteristic OH mode of talc hydroxyl groups bound to the talc octahedral layer . The additional peak at 3663.4 cm –1 may indicate a slight octahedral distortion, which leads to the splitting of the MgO–OH mode, or iron contamination in the talc octahedral layer. However, the latter is less likely to be the cause, as the measured Raman shift of the talc fundamental peaks of our sample agree with that of high-quality standard talc samples, without any indication of iron impurities or the three characteristic Fe–OH modes near 3678 cm –1 in iron-rich talc …”

“…The additional peak at 3663.4 cm –1 may indicate a slight octahedral distortion, which leads to the splitting of the MgO–OH mode, or iron contamination in the talc octahedral layer. However, the latter is less likely to be the cause, as the measured Raman shift of the talc fundamental peaks of our sample agree with that of high-quality standard talc samples, without any indication of iron impurities or the three characteristic Fe–OH modes near 3678 cm –1 in iron-rich talc Figure b shows the DFPT-simulated Raman spectrum of bulk talc, showing excellent agreement between theory and the experiment (see Table and the Supporting Information, where we compare the results for the bulk talc Raman-active modes obtained by using PBEsol and rVV10 functionals).…”

“…The Raman peaks at 194.5 cm -1 , 362.1 cm -1 , 676.2 cm -1 and 1050.5 cm -1 are ascribed to the fundamental vibrations of silicates in talc, and the peak at 3678.8 cm -1 is the characteristic OH mode of talc hydroxyl groups bound to the talc octahedral layer 69 . The additional peak at 3663.4 cm -1 may indicate a slight octahedral distortion 69 , which leads to the splitting of the MgO-OH mode, or iron contamination in the talc octahedral layer 70,71 .…”

“…Monolayer (1L) and few-layer (FL) talc have recently revealed interesting magnetic, optical, − electrical, ,,, and mechanical ,− properties as a single material and when combined with other LMs in van der Waals heterostructures (vdWHs). Although the structural properties of talc have been investigated previously, ,,− ,, to the best of our knowledge, no work has fully described its Raman and far-infrared (Far-IR) active modes in the ultrathin form (Figure d) as a function of layer thickness. Here, we investigate the structural and vibrational properties of talc layers, from their ultrathin form to bulk scale using ab initio calculations, Raman spectroscopy, and synchrotron infrared nanospectroscopy (SINS).…”

Phyllosilicates as earth-abundant layered materials for electronics and optoelectronics: Prospects and challenges in their ultrathin limit

“…One of the challenges in using naturally occurring vdWs materials for 2D-based applications is the existence of impurities and defects in their crystal lattice. 2,20,22,27,29,[35][36][37] There can be point defects (e.g., vacancies, substitutional or interstitial impurities) or extended defects (e.g., grain boundaries, twin planes…”