Spin fluctuation and the paramagnetic-ferromagnetic transition in (Pd₉₅Rh₅)1-xNixalloys

Low-temperature (1-20K) low-field (1/2-4 kG) magnetisation and low-temperature (1-20K) zero-field electrical resistivity measurements have been made on a series of (Pd95Rh5)1-xNix alloys (x<or=0.03). At 4K the magnetisation measurements were extended to 56 kG and in the case of the more dilute alloys the resistivity measurements were extended to 300K. Curie temperatures and spontaneous magnetisation obtained by an Arrott plot analysis of the magnetisation data yield a critical concentration for the onset of ferromagnetism of 1.9+or-0.05 at.% Ni. In the paramagnetic region the magnetisation, susceptibility (dM/dH) and resistivity are well fitted by a model which considers local spin fluctuations to be associated with two types of magnetic centre: a pair of interacting Ni atoms and a single non-interacting Ni atom. The local enhancement associated with a Ni pair is found to be roughly three to four times as large as that of a non-interacting Ni atom.