Helimagnet FeP中的阻挫模型和自旋激发
Frustration model and spin excitations in the helimagnet FeP
摘要：
金属化合物FeP属于具有由磁阻挫驱动的复杂非共线自旋序的材料类别。虽然它的双螺旋磁性结构与周期$λ_{\text{s}} \approx 5c$，其中$c$是晶格常数，以前确定，相关的自旋自旋相互作用，导致该基态仍然未知。通过进行广泛的非弹性中子散射测量，我们获得了自旋激发谱的动量-能量空间的很大一部分。谱图表明磁振子带隙能量为$\sim$ 5 meV。尽管三维晶体结构，磁振子模式显示强烈的各向异性色散，揭示了准一维字符的磁性相互作用FeP。然而，材料的物理性质并不是由占主导地位的交换决定的，它是铁磁性的。相反，刚性铁磁自旋链之间较弱的二维反铁磁相互作用驱动磁阻挫。使用线性自旋波理论，我们能够构建一个有效的海森堡哈密顿量与各向异性项能够再现所观察到的光谱。这使我们能够量化FeP中的交换相互作用，并确定其磁阻挫的机制。
英文摘要：
The metallic compound FeP belongs to the class of materials that feature a complex noncollinear spin order driven by magnetic frustration. While its double-helix magnetic structure with a period $λ_{\text{s}} \approx 5c$, where $c$ is the lattice constant, was previously well determined, the relevant spin-spin interactions that lead to that ground state remain unknown. By performing extensive inelastic neutron scattering measurements, we obtained the spin-excitation spectra in a large part of the momentum-energy space. The spectra show that the magnons are gapped with a gap energy of $\sim$5 meV. Despite the 3D crystal structure, the magnon modes display strongly anisotropic dispersions, revealing a quasi-one-dimensional character of the magnetic interactions in FeP. The physics of the material, however, is not determined by the dominating exchange, which is ferromagnetic. Instead, the weaker two-dimensional antiferromagnetic interactions between the rigid ferromagnetic spin chains drive the magnetic frustration. Using linear spin-wave theory, we were able to construct an effective Heisenberg Hamiltonian with an anisotropy term capable of reproducing the observed spectra. This enabled us to quantify the exchange interactions in FeP and determine the mechanism of its magnetic frustration.
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