The spin excitations of the block-antiferromagnetic K$_{0.8}$Fe$_{1.6}$Se$_2$

TL;DR

This paper investigates the spin excitation spectrum of the block-antiferromagnetic K$_{0.8}$Fe$_{1.6}$Se$_2$ using an effective Hamiltonian, revealing multiple spin wave branches and calculating related magnetic properties.

Contribution

It introduces a detailed analysis of spin excitations in K$_{0.8}$Fe$_{1.6}$Se$_2$, highlighting the existence of optical-like spin wave branches and computing magnetic susceptibilities.

Findings

Existence of four spin wave branches, including three optical modes.

Calculation of spin wave corrected magnetic moments.

Determination of uniform spin susceptibilities.

Abstract

We study the spin excitations of the newly discovered block-antiferromagnetic state in K$_{0.8}$Fe$_{1.6}$Se$_2$ using an effective spin Hamiltonian suggested in the literature. Interestingly in addition to the usual Goldstone mode, there exists three other "optical" spin wave branches. These spin excitations are the analog of "optical phonons" in crystals with more than one atom per unit cell. We compute the spin wave corrected ordering moment and the uniform spin susceptibilities.