Abstract
The ground state phase diagram, the physical properties of spin waves and the dynamic structure factor of the new family of 122 iron-vacancy ordered compound K2Fe7Se8 are theoretically investigated based on the J1–J2 Heisenberg model. Four antiferromagnetic phases are found to be stable in the reasonable physical parameter region. The dispersion relations of the spin waves for the newly discovered AFM2 and AFM3 phases are studied using the linearized spin wave theory. Two acoustic spin wave branches and 12 optical spin wave branches are present in both the AFM2 and AFM3 phases, and each of them are twofold degenerate. One more interesting finding is that the spin waves of K2Fe7Se8 have the quasi-one-dimensional character at the high frequency range. To offer theoretical guidance for the further neutron scattering experiments, the inelastic neutron scattering patterns for the AFM2 and AFM3 phases are also investigated.
Highlights
The ground state phase diagram, the physical properties of spin waves and the dynamic structure factor of the new family of 122 iron-vacancy ordered compound K2Fe7Se8 are theoretically investigated based on the J1–J2 Heisenberg model
Using the linear spin wave theory, we have investigated the dispersion relations of the spin wave for the newly discovered AFM2 and AFM3 phases, which have two acoustic spin wave branches and 12 optical spin wave branches
Owing to four different parameters in the J1–J2 Heisenberg model, the phase diagram is plotted in the J1 − J2 space while other parameters are fixed, i.e. J1 = ±1 and J2 = 1
Summary
The ground state phase diagram, the physical properties of spin waves and the dynamic structure factor of the new family of 122 iron-vacancy ordered compound K2Fe7Se8 are theoretically investigated based on the J1–J2 Heisenberg model. When the spin coupling J1 is dominant in the parameter region (i.e. J1 → −∞), J1 favors the FM magnetic configuration along the diagonal direction around the centered Fe vacancy, which induces the super-moment. To give a qualitatively understanding of the newly discovered AFM2 and AFM3 phases, we will discuss their spin wave characters based on the linear spin wave theory.
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