Spin Fluctuations and the Paramagnetic-Ferromagnetic Transition in Palladium-Rhodium-Nickel Alloys.

Low-temperature 1-20 K low-field 12-4 kG magnetization and low-temperature 1-20 K zero-field electrical resistivity measurements have been made on a series of Pd95Rh51-xNix alloys x or 0.03. At 4 K the magnetization measurements were extended to 56 kG, and in the case of the more dilute alloys the resistivity measurements were extended to 300 K. Curie temperatures and spontaneous magnetization obtained by an Arrott plot analysis of the magnetization data yield a critical concentration for the onset of ferromagnetism of 1.9 or - 0.05 at Ni. In the paramagnetic region the magnetization, susceptibility dMdH, and resistivity are well fitted by a model which considers local spin fluctuations to be associated with two types of magnetic center a pair of interacting Ni atoms and a single noninteracting Ni atom. The local enhancement associated with a Ni pair is found to be roughly 3 to 4 times as large as that of a noninteracting Ni atom. The spin-fluctuation temperature and the characteristic-field parameter are, respectively, T sub s 59 or - 4 K and H sub s 225 or - 25 kG for the noninteracting Ni atom, and T sub s 18 or - 8 K and H sub s 35 or - 5 kG for the Ni pair. In the ferromagnetic alloys the magnetization of a large number of the Ni atoms appears to remain unsaturated at 4 K. The results for this system are compared with corresponding results for the Pd1-xNix system. Author