Degradation Chemistry and Kinetic Stabilization of Magnetic CrI₃

Abstract

The discovery of the intrinsic magnetic order in single-layer chromium trihalides (CrX3, X = I, Br, and Cl) has drawn intensive interest due to their potential application in spintronic devices. However, the notorious environmental instability of this class of materials under ambient conditions renders their device fabrication and practical application extremely challenging. Here, we performed a systematic investigation of the degradation chemistry of chromium iodide (CrI3), the most studied among CrX3 families, via a joint spectroscopic and microscopic analysis of the structural and composition evolution of bulk and exfoliated nanoflakes in different environments. Unlike other air-sensitive 2D materials, CrI3 undergoes a pseudo-first-order hydrolysis in the presence of pure water toward the formation of amorphous Cr­(OH)3 and hydrogen iodide (HI) with a rate constant of k I = 0.63 day–1 without light. In contrast, a faster pseudo-first-order surface oxidation of CrI3 occurs in a pure O2 environment, generating CrO3 and I2 with a large rate constant of k Cr = 4.2 day–1. Both hydrolysis and surface oxidation of CrI3 can be accelerated via light irradiation, resulting in its ultrafast degradation in air. The new chemical insights obtained allow for the design of an effective stabilization strategy for CrI3 with preserved optical and magnetic properties. The use of organic acid solvents (e.g., formic acid) as reversible capping agents ensures that CrI3 nanoflakes remain stable beyond 1 month due to the effective suppression of both hydrolysis and oxidation of CrI3.

Probing Defects and Spin‐Phonon Coupling in CrSBr via Resonant Raman Scattering

“…This likely is similar to the degradation mechanisms in CrI 3 , where hydrolysis and oxidation were demonstrated to result in the formation of Cr(OH) 3 and CrO 3 respectively. [ 58 ] Given that in this work, water and air exposure yield a similar defect response, we hypothesize that hydrolysis is the primary defect mechanism observed also given the strong effect when submerged in water.…”

Strongly Correlated Exciton‐Magnetization System for Optical Spin Pumping in CrBr3 and CrI3.

“…The observable PL arises due to the brightening of dark excitons. Based on the composition of the excitonic wave function in combination with the comparative analysis of PL and PLE spectra we identify two brightening mechanisms: 1) admixtures of bright p ‐type orbitals of the halide atoms into the excitonic wave function which gives rise to the ZPL [ 54,55 ] and 2) recombination/creation of dark ψCr, d state through many‐body processes with the emission/absorption of phonons. The latter processes give rise to broad emission/absorption bands at the lower/higher energy side of the ZPL as highlighted in Figure 1a.…”

Capturing 2D van der Waals magnets with high probability for experimental demonstration from materials science literature

“…This application has a revolutionary impact on information technologies 1–15 . However, there are a few challenging issues on the road to the practical applications of 2D vdW magnets, such as poor ambient stability and low magnetic transition temperature 16–20 . New 2D vdW magnets may provide unprecedented opportunities for tackling these issues and bring fascinating physical phenomena, providing novel platforms for studying the intrinsic mechanisms of magnetism.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] However, there are a few challenging issues on the road to the practical applications of 2D vdW magnets, such as poor ambient stability and low magnetic transition temperature. [16][17][18][19][20] New 2D vdW magnets may provide unprecedented opportunities for tackling these issues and bring fascinating physical phenomena, providing novel platforms for studying the intrinsic mechanisms of magnetism. Machine learning (ML) techniques and density functional theory (DFT) calculations have been widely utilized to accelerate the discovery of 2D vdW magnets.…”