Anomalous magnetic behavior of Ce1−xMxCo5(M=Zr,Hf) alloys

The compound CeCo₅ is ferromagnetically ordered with a Curie temperature (T_c) of 641 K and a moment (μ_Co) of 1.36μ_B per Co atom at 77 K. Replacement of Ce by Hf or Zr in CeCo₅ reduces the magnetic moment on cobalt but substantially increases the Curie temperature. For instance, in Ce_0.8Hf_0.2Co₅μ_Co=1.12μ_B at 77 K and T_c=846 K. These results indicate a much stronger d-d electron interaction in the ternary alloys than in CeCo₅. Ce in these systems behaves as if it is nearly quadrivalent.