Size-Dependent Critical Temperature and Anomalous Optical Dispersion in Ferromagnetic CrI₃ Nanotubes.

Mohammed Moaied,Jisang Hong

doi:10.3390/nano9020153

Abstract

Using first principles calculations, we explored the magnetic and optical properties of chromium(III) iodide (CrI3) nanotubes (NTs) by changing their chirality and diameter. Here, we considered six types of NTs: (5,0), (5,5), (7,0), (10,0), (10,10), and (12,0) NTs. We found that both zigzag and armchair NTs had a ferromagnetic ground with a direct band gap, although the band gap was dependent on the chirality and diameter. Using the Monte Carlo simulation, we found that the Curie temperatures (Tc) exhibited chirality and diameter dependence. In zigzag NTs, the larger the tube diameter, the larger the Tc, while it decreased with increasing diameter in the armchair tube. We found that the Tc was almost doubled when the diameter increased two-fold. This finding may guide development of room temperature ferromagnetism in zigzag NTs. We also found that the CrI3 NTs displayed anisotropic optical properties and anomalous optical dispersion in the visible range. Specifically, the (10,0) zigzag NT had a large refractive index of 2 near the infrared region, while it became about 1.4 near blue light wavelengths. We also obtained large reflectivity in the ultraviolet region, which can be utilized for UV protection. Overall, we propose that the CrI3 NTs have multifunctional physical properties for spintronics and optical applications.

Highlights

Extensive studies have focused on two-dimensional (2D) materials because they display many peculiar physical properties not found in bulk or macroscopic structures
We found that all CrI3 NT systems had a direct band gap with a ferromagnetic ground state, and the band gap was dependent on the chirality and the diameter
The band gap of zigzag NTs was increased with larger diameter, while the armchair NT showed the opposite trend

Summary

Introduction

Extensive studies have focused on two-dimensional (2D) materials because they display many peculiar physical properties not found in bulk or macroscopic structures. Numerous types of 2D materials have been fabricated Most of these are non-magnetic, few theoretical works have investigated the physical properties of magnetic 2D structures. It was recently reported that the chromium(III) iodide (CrI3) monolayer has a finite band gap of 1.2 eV with an FM ground state. The pristine CrI3 layer consists of three monoatomic planes: one plane of chromium (Cr) atoms sandwiched between two atomic planes of iodine (I). The Cr in the pristine CrI3 layer is expected to have a +3 state with an electron configuration of 3d34s0. This is consistent with the observed saturation magnetization of CrI3, which has a magnetic moment of around 3 μB per Cr atom [2]

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Conclusion