CrI₃ magnetic nanotubes: A comparative DFT and DFT+U study, and strain effect

In this paper, structural and electronic properties of CrI₃ magnetic nanotubes (NTs) are studied using density functional theory. Both armchair and zigzag CrI₃ nanotubes demonstrate a high correlation in strain energy between each other independently on accounting the Hubbard correction. The strain energies decrease with expansion of the tube diameter making the tubes’ synthesis with a diameter larger than 45 Å to be energetically possible. The nanotubes of both zigzag and armchair chirality are ferromagnetic semiconductors with band gaps close to that of the CrI₃ monolayer. The band gaps are suppressed by reducing the tube diameters due to the structural stress leading to deformation of the Cr–I crystal field and changes in the bond lengths. The external strain can be utilized to flexibly tune the electronic properties of CrI₃ nanotubes with the desired spin-up/spin-down band gap ratio. Strong distortion of the octahedral Cr–I crystal field under compression results in nontrivial behavior in the spin-up band gap of (4, 4) tube. Stretching of tubes leads to the enhancement of the exchange energy that should result in higher Curie temperature, therefore providing a good platform for potential applications in spintronic nanodevices.