Short-range magnetic order and effective suppression of superconductivity by manganese doping in LaFe1-xMnxAsO1-yFy

We present a study of the structural and physical properties of directly hole-doped LaFe1-xMnxAsO (x = 0.0 -0.2) and the influence of charge compensation by additional F doping in LaFe0.9Mn0.1AsO1-yFy (y = 0.1 -0.5). High-quality polycrystalline samples were prepared for Mn-doped LaFe1-xMnxAsO and the low doping regime in LaFe0.9Mn0.1AsO1-yFy (y = 0.1 and 0.2) using a solid-state metathesis reaction. The unit cell increases upon Mn doping, but decreases again when additional F is inserted. The semiconducting character of LaFe1-xMnxAsO decreases with additional F doping. Muon spin relaxation (mu SR) measurements reveal short-range magnetic order in LaFe1-xMnxAsO and a suppression of magnetism by additional electron doping with fluoride in LaFe0.9Mn0.1AsO1-yFy. Superconductivity remains absent even though the electronic preconditions are fulfilled in electron-doped LaFe0.9Mn0.1AsO1-yFy at x > 0.1, which is suggestive of effective pair breaking by Mn in this system.