Unified spin model for magnetic excitations in iron chalcogenides

Abstract

Recent inelastic neutron scattering (INS) measurements on FeSe and Fe(Te 1−x Se x ) have sparked intense debate over the nature of the ground state in these materials. Here we propose an effective bilinear-biquadratic spin model, which is shown to consistently describe the evolution of low-energy spin excitations in FeSe, both under applied pressure and upon Se/Te substitution. The phase diagram, studied using a combination of variational mean-field, flavor-wave calculations and density-matrix renormalization group (DMRG), exhibits a sequence of transitions between the columnar antiferromagnet common to the iron pnictides, the nonmagnetic ferroquadrupolar phase attributed to FeSe, and the double-stripe antiferromagnetic order known to exist in Fe 1+y Te. The calculated spin structure factor in these phases mimics closely that observed with INS in the Fe(Te 1−x Se x ) series. In addition to the experimentally established phases, the possibility of incommensurate magnetic order is also predicted.

Noncollinear antiferromagnetic order and effect of spin-orbit coupling in spin-1 honeycomb lattice

“…relatively large values of K 1 from first-principles calculations [25,26], and it turns out to be essential to correctly describe the magnon dispersion in inelastic neutron scattering [27][28][29][30]. In the present case, we shall show that the presence of the K 1 term affects the relative stability of the Néel and noncollinear magnetic states (see Sec.…”

Noncollinear Antiferromagnetic Order and Effect of Spin-Orbit Coupling in Spin-1 Honeycomb Lattice

“…( 1) is important to correctly capture the physics of spin 1 interactions, as was proven to be the case in other 3d metals with spin-1 moments, notably the iron pnictides and chalcogenides. There, one also finds negative and relatively large values of K 1 from first principles caculations 30,31 , and it turns out to be essential to correctly describe the magnon dispersion in inelastic neutron scattering [32][33][34][35] . In the present case, we shall show that the presence of K 1 term affects the relative stability of the Néel and noncollinear magnetic states (see section V B).…”