Unconventional ferrimagnetism and enhanced magnetic ordering temperature in monolayer CrCl₃ by introducing O impurities and Cl vacancies

Abstract

Among chromium trihalides, a specific group of layered van der Waals magnetic materials, chromium trichloride (CrCl3) is the only system relatively stable under ambient conditions. This is also observed in reduced dimensionality where the emergence of extrinsic long-range ordered oxidized and Cl-vacancy-defective CrCl3 phases is experimentally reported. In this work, the magnetic properties of such extrinsic two-dimensional (2D) systems are studied using density functional theory (DFT) calculations, including the electron-electron (U) repulsion interactions, and Monte Carlo (MC) simulations. Once the Cl vacancies are introduced, the results indicate that the monolayer CrCl3 has a magnetic moment that is enhanced linearly (up to 3.14 μB/Cr) in the (1-10 %) vacancy concentration range. This determines a strengthening of the ferromagnetic state and a two-fold increase of the Curie temperature (up to 146 K) as valuated from MC simulations. More interestingly, once oxygen extrinsic impurities are considered, the monolayer CrCl3 structure is hybridized forming a stable ordered phase (O-CrCl3) with oxygen atoms allocated on the Cr atomic layer in the center of the honeycomb ring formed by Cr atoms. The magnetic moments of the O-CrCl3 system are localized on both Cr and O atoms, with oxygen which is antiferromagnetically coupled with chromium, resulting in a 2D ferrimagnetic hexagonal lattice system with an average magnetic moment of 2.14 μB/Cr and a high magnetic ordering temperature (110 K) predicted with DFT in the mean field approach.

Two-Dimensional CrCl3-Layered Trihalide Nanoflake Sensor for the Detection of Humidity, NO2, and H2

“…Like zeolites and metal–organic frameworks (MOFs), monolayered TMTHs such as CrCl 3 can be classified as 2D microporous materials ( D pore < 2 nm) because of the presence of intrinsic atomic pores in a size range of 1.53–1.94 Å, as indicated by the dotted-black squares in Figure a . These empty cages, located at the center of the honeycomb lattice formed by Cr atoms (Figure a), similar to the model of Li adsorption over CrI 3 , can be spontaneously filled by ambient oxygen (red spheres in Figure a), resulting in the formation of an ordered semioxidized O–CrCl 3 surface phase, with oxygen impurities intercalated in the Cr atomic layer under ambient conditions, as recently demonstrated by theoretical and experimental observations. ,, Moreover, the presence of Cl vacancies in 2D-CrCl 3 flakes must be also considered, as indicated by the dotted-black circles in Figure a, which are energetically favorable, as proven in refs , . Consequently, the presence of the O–CrCl 3 phase and Cl vacancies induces a partial electron charge transfer from O and Cl atoms to Cr, ,, eventually encouraging the electrostatic interactions of ambient molecules over preferential atomic polar sites.…”