Frustration model and spin excitations in the helimagnet FeP

Abstract

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 s ≈ 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 ∼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.

Systematic determination of a material’s magnetic ground state from first principles

“…Instead, a spin canting effect emerges, affecting half of the magnetic moments in the unit cell, causing them to rotate by an angle of θ = 4.19 ∘ . This spin canting angle aligns with the findings of various experimental studies on FeP 33,34 , which report a value of ~4∘ .…”

“…6a). This indicates the instability of the ferromagnetic configuration and aligns with the reported antiferromagnetic structure characterized by the propagation vector (0.0, 0.0, 0.2) 33 . From this, we automatically generate a 1 × 1 × 5 supercell (see the end of "Magnetic Ground State Workflow") containing a spin spiral A value of U = 3 eV has been used.…”

Systematic determination of a material's magnetic ground state from first principles

“…Instead, a spin canting effect emerges, affecting half of the magnetic moments in the unit cell, causing them to rotate by an angle of θ = 4.19°. This spin canting angle aligns with the findings of various experimental studies on FeP [29,30], which report a value of approximately 4°.…”

“…We observe that the dispersion of h(k) exhibits negative eigenvalues and a global minimum at k min = (0.00, 0.03, 0.21) (top part of Figure 6). This in-dicates the instability of the ferromagnetic configuration and aligns with the reported antiferromagnetic structure characterized by the propagation vector (0.0, 0.0, 0.2) [29]. From this, we automatically generate a 1 × 1 × 5 supercells (see the end of section III) containing a spin spiral magnetic structure.…”

Superlattices of Gadolinium and Bismuth Based Thallium Dichalcogenides as Potential Magnetic Topological Insulators

“…Another possibility is that the interlayer configuration is helimagnetic, which is compatible with the interlayer magnetic frustration [ 99 , 100 ]. It would also be in line with the results of the electron paramagnetic resonance study of TlGdSe [ 75 ], pointing towards a possible helimagnetic state.…”