Magnetic exchange interactions in monolayer CrI₃ from many-body wavefunction calculations
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The marked interplay between the crystalline, electronic, and magnetic structure of atomically thin magnets has been regarded as the key feature for designing next-generation magneto-optoelectronic devices. In this respect, a detailed understanding of the microscopic interactions underlying the magnetic response of these crystals is of primary importance. Here, we combine model Hamiltonians with multireference configuration interaction wavefunctions to accurately determine the strength of the spin couplings in the prototypical single-layer magnet CrI₃. Our calculations identify the (ferromagnetic) Heisenberg exchange interaction J = −1.44 meV as the dominant term, being the inter-site magnetic anisotropies substantially weaker. We also find that single-layer CrI₃ features an out-of-plane easy axis ensuing from a single-ion anisotropy A = −0.10 meV, and predict g-tensor in-plane components gxx = gyy = 1.90 and out-of-plane component gzz = 1.92. In addition, we assess the performance of a dozen widely used density functionals against our accurate correlated wavefunctions calculations and available experimental data, thereby establishing reference results for future first-principles investigations. Overall, our findings offer a firm theoretical ground to recent experimental observations.
原子级薄层磁体的晶体结构、电子结构与磁结构之间存在显著的相互耦合作用，这被认为是设计下一代磁光电子器件的核心特性。鉴于此，深入理解这类晶体磁响应背后的微观相互作用至关重要。本研究将模型哈密顿量与多参考组态相互作用波函数相结合，精准测定了典型单层磁体CrI₃中的自旋耦合强度。计算结果表明，（铁磁性）海森堡交换相互作用J = −1.44 meV为主要项，而位点间磁各向异性的强度则显著更弱。本研究还发现，单层CrI₃具有由单离子各向异性A = −0.10 meV引发的面外易磁化轴，并预测其g张量的面内分量gxx = gyy = 1.90，面外分量gzz = 1.92。此外，本研究以精准的关联波函数计算结果与已公开实验数据为基准，评估了十余种常用密度泛函的计算性能，从而为未来的第一性原理研究确立了参考标准。综上，本研究的发现为近期的实验观测结果提供了坚实的理论依据。
