Magnetic Properties Controlled by Interstitial or Interlayer Cations in Iron Chalcogenides

TL;DR

This study uses density functional theory to show that interstitial and interlayer cations influence magnetic order and instability in iron chalcogenides, revealing their roles in magnetic phase transitions and potential superconductivity.

Contribution

It demonstrates how interstitial and interlayer cations control magnetic properties and phase transitions in iron chalcogenides, highlighting their importance in understanding superconductivity mechanisms.

Findings

Magnetic phases in Fe$_{1+y}$Te vary with interstitial iron concentration.

Magnetic instability at $( ext{ extpi}, ext{ extpi})$ is enhanced at low $y$ in K$_y$Fe$_2$Se$_2$.

Itinerant electrons are crucial in iron chalcogenides, similar to iron pnictides.

Abstract

By applying density functional theory calculations to iron chalcogenides, we find that magnetic order in Fe$_{1+y}$Te and magnetic instability at $(\pi,\pi)$ in K$_y$Fe$_2$Se$_2$ are controlled by interstitial and interlayer cations, respectively. While in Fe$_{1+y}$Te, magnetic phase transitions occur among collinear, exotic bicollinear and plaquette-ordered antiferronmagnetic states when the height of interstitial irons measured from iron plane or the concentration of interstitial irons is varied, the magnetic instability at $(\pi,\pi)$ which is believed to be responsible for the Cooper pairing in iron pnictides is significantly enhanced when $y$ is much smaller than $1$ in K$_y$Fe$_2$Se$_2$. Our results indicate that, similar to iron pnictides, itinerant electrons play important roles in iron chalcogenides, even though the fluctuating local moments become larger.