Effect of 3d Transition Metal Doping on the Superconductivity in Quaternary Fluoroarsenide CaFeAsF

TL;DR

This study investigates how doping CaFeAsF with 3d transition metals affects its superconductivity, revealing that Co and Ni induce superconductivity while Cr, Mn, and Cu do not, due to their different electronic roles.

Contribution

It provides new insights into the effects of 3d transition metal doping on superconductivity in CaFeAsF, highlighting the roles of electron donation and scattering.

Findings

Co and Ni doping induce superconductivity with maximum T_c of 22 K and 12 K.

Cr, Mn, and Cu doping do not induce superconductivity and act as scattering centers.

Doping alters lattice constants and electronic properties, affecting superconductivity.

Abstract

We examined doping effect of 3d transition metal elements (TM: Cr, Mn, Co, Ni, and Cu) at the Fe site of a quaternary fluoroarsenide CaFeAsF, an analogue of 1111-type parent compound LaFeAsO. The anomaly at ~120 K observed in resistivity (rho) vs. temperature (T) plot for the parent compound is suppressed by the doping of each TM element. Furthermore, Co- and Ni-doping (CaFe1-xTMxAsF, TM = Co, Ni) induces superconductivity with a transition temperature maximized at the nominal x = 0.10 for Co (22 K) and at x = 0.05 for Ni (12 K). These optimal doping levels may be understood by considering that Ni2+(3d8) adds double electrons to the FeAs layers compared with Co2+ (3d7). Increased x for Co or Ni breaks the superconductivity while metallic nature drho/dT > 0 is still kept. These observations indicate that Co and Ni work as electron donors. In contrast, neither of Cr, Mn nor Cu-doping induce superconductivity, yielding drho/dT < 0 in the below the rho-T anomaly temperature, indicating that these transition metal ions act as scattering centers. The two different behavior of TM replacing the Fe site is discussed in relation to the changes in the lattice constants with the doping.