Gd Mössbauer effect and magnetic properties of GdCo5-χGaχ

We have investigated the effect of Ga substitution on the magnetic properties and the ¹⁵⁵Gd Mössbauer spectra of GdCo₅. A substantial increase was observed in the values of the electric field gradient derived from the quadrupole splitting of the spectra. This was ascribed to a preferred substitution of Ga into the 2c Co site in GdCo₅. This preferred Ga substitution also led to a change in the easy magnetization direction from parallel to the c axis (GdCo₅) to perpendicular to the c axis (GdCo₃Ga₂). Increasing the amount of Ga substitution was found to decrease strongly the magnetic ordering temperature and the Co-induced transferred Gd hyperfine field in the series GdCo_5-χGa_χ.