Magnetic anisotropy in ferromagnetic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>CrI</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>
Lebing Chen, Jae-Ho Chung, Tong Chen, Chunruo Duan, A. Schneidewind, I. Radelytskyi, David Voneshen, R. A. Ewings, M. B. Stone, А. И. Колесников, Barry Winn, Songxue Chi, Richard A. Mole, Dehong Yu, Bin Gao, Pengcheng Dai
Abstract
We use neutron scattering to show that ferromagnetic (FM) phase transition in the two-dimensional (2D) honeycomb lattice ${\mathrm{CrI}}_{3}$ is a weakly first order transition and controlled by spin-orbit coupling (SOC) induced magnetic anisotropy, instead of magnetic exchange coupling as in a conventional ferromagnet. With increasing temperature, the magnitude of magnetic anisotropy, seen as a spin gap at the Brillouin zone center, decreases in a power law fashion and vanishes at ${T}_{C}$, while the in-plane and $c$-axis spin-wave stiffnesses associated with magnetic exchange couplings remain robust at ${T}_{C}$. We also compare parameter regimes where spin waves in ${\mathrm{CrI}}_{3}$ can be described by a Heisenberg Hamiltonian with Dzyaloshinskii-Moriya interaction or a Heisenberg-Kitaev Hamiltonian. These results suggest that the SOC induced magnetic anisotropy plays a dominant role in stabilizing the FM order in single layer 2D van der Waals ferromagnets.