Abstract
Single crystals of Na1-delta (Fe1-x T (x) )As with T = Pd, Ni, Cr, and Mn were investigated by magnetic susceptibility, specific heat, and electronic transport measurements. The structural and spin density wave phase transitions are completely suppressed when Fe in NaFeAs is substituted by those different heterovalent dopings. While superconductivity is only observed for formal electron doping (viz. by substituting Fe with either Pd or Ni), a non-superconducting phase down to 1.8 K is achieved by formal hole doping when Fe is substituted by Cr or Mn in NaFeAs along with the formation of a magnetic phase. This magnetic phase has also strong impact on the material properties.