Two-Dimensional van der Waals Nanoplatelets with Robust Ferromagnetism

Abstract

We have synthesized unique colloidal nanoplatelets of the ferromagnetic twodimensional (2D) van der Waals material CrI 3 and have characterized these nanoplatelets structurally, magnetically, and by magnetic circular dichroism spectroscopy. The isolated CrI 3 nanoplatelets have lateral dimensions of ~25 nm and ensemble thicknesses of only ~4 nm, corresponding to just a few CrI 3 monolayers. Magnetic and magneto-optical measurements demonstrate robust 2D ferromagnetic ordering in these nanoplatelets with Curie temperatures similar to those observed in bulk CrI 3 , despite the strong spatial confinement. These data also show magnetization steps akin to those observed in micron-sized few-layer 2D sheets and associated with concerted spin-reversal of individual CrI 3 layers within few-layer van der Waals stacks. Similar data have also been obtained for CrBr 3 and anion-alloyed Cr(I 1-x Br x ) 3 nanoplatelets. These results represent the first example of laterally confined 2D van der Waals ferromagnets of any composition. The demonstration of robust ferromagnetism at nanometer lateral dimensions opens new doors for miniaturization in spintronics devices based on van der Waals ferromagnets.

Magnetic Two-Dimensional Chromium Trihalides: A Theoretical Perspective

“…Open theory questions such as how quantum fluctuations that prevent broken symmetry in 1D structures, such as CrX 3 nanotubes and nanoribbons, may become relevant if these structures are fabricated. This is something to keep in mind, given the recent report on 0D CrI 3 nanoplatelets …”

A Femtosecond Magnetic Circular Dichroism Spectrometer

“…In addition to dielectrics, other new materials in ultrafast magnetism are now being pursued, such as magnetoplasmonic crystals, 11,12 molecule-based magnets, 13 and a) olof.johansson@ed.ac.uk two-dimensional ferromagnets. 14,15 However, much of the research devoted to ultrafast magneto-optics to date has only considered quasi-monochromatic light because of the lack of spectral features in reflectance and transmission spectra of metallic samples.…”

Strength of effective Coulomb interaction in two-dimensional transition-metal Halides MX$_2$ and MX$_3$ (M=Ti, V, Cr, Mn, Fe, Co, Ni; X=Cl, Br, I)

“…First-principles theoretical studies have predicted that the long-range magnetic order is also possible in other 2D monolayers of TM dihalides and trihalides (MX 2 and MX 3 , M = V, Cr, Mn, Fe and Ni, and X=Cl, Br and I) [31][32][33][34][35][36][37][38][39][40][41]. Besides CrI 3 , ferromagnetic order in the other TM halides such as CrCl 3 [42], CrBr 3 [43,44], NiI 2 [45], and VI 3 [46,47] monolayers were discovered experimentally and confirmed theoretically [48,[50][51][52][53].…”