Magnetic Properties Controlled by Interstitial or Interlayer Cations in Iron Chalcogenides

By applying density functional theory calculations to iron chalcogenides, we find that magnetic order in Fe(1+y)Te and magnetic instability at (π, π) 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 (π, π) 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.