Spin excitations in K$_{0.84}$Fe$_{1.99}$Se$_2$ superconductor as studied by M\"ossbauer spectroscopy

TL;DR

This study uses Mössbauer spectroscopy to investigate spin excitations and magnetic structure in the K$_{0.84}$Fe$_{1.99}$Se$_2$ superconductor, revealing a spin excitation gap and insights into magnetic interactions.

Contribution

It provides site-specific magnetic information and models the magnetic interactions, highlighting the coexistence of superconductivity and magnetism in this material.

Findings

Detection of a spin excitation gap of approximately 5 meV.

Confirmation of ferromagnetically coupled spin blocks with antiferromagnetic interactions.

Reproduction of hyperfine magnetic field temperature dependence using a simple theoretical model.

Abstract

M\"ossbauer spectroscopy was used to probe the site specific information of the $K_{0.84}Fe_{1.99}Se_2$ superconductor. Possibility of coexistence of superconductivity and magnetism is discussed. A spin excitation gap, $\Delta E \approx$5\,meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field (HMF) at the iron site within the spin wave theory. Using a simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the iron-selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.