Matrix and Impurity-Cluster Polarization in Ni-Pt and Ni-Pd Alloys

A study of hyperfine magnetic fields at nuclei of ⁵⁷Fe diffused as impurities in the transition-metal alloys Ni-Pt and Ni-Pd and at nuclei of ⁶¹Ni in the Ni-Pt system has been carried out using the M\"ossbauer-effect technique. The fields were measured as a function of composition and temperature on the atomically disordered alloys. The experimentally determined Curie temperatures TC and saturation hyperfine fields are presented for the entire composition range of each system. Analysis of the M\"ossbauer spectra of specific samples for various diffusion times of the ⁵⁷Fe traces gives clear indication of iron impurity clustering within the Ni-Pd and Ni-Pt alloy matrices. A simple phenomenological theory is presented in an attempt to explain the TC vs concentration dependence in these alloys.