Competitive contributions of short-range magnetic order and chemical disorder to the resistivity in Co30Pt70

A comparative study of the dependence on T of the resistivity in non-magnetic Ni 30 Pt 70 and paramagnetic Co 30 Pt 70 alloys in their ordered (L1 2 -type structure) and disordered (A 1 ) phase is presented. In order to make measurements of as far as possible real thermodynamic equilibrium states, the heating rates were chosen taking into account previous (Co 30 Pt 70 ) or present (Ni 30 Pt 70 ) order kinetics data. The authors find that in Ni 30 Pt 70 the resistivity can be analysed in terms of two main contributions: (i) a term of 4 K residual resistivity associated with the chemical disorder, and its variation with T, which is separately measured using a specific device; and (ii) a phonon-like term, proportional to T. In Co 30 Pt 70 , a further term associated with the spin-disorder scattering at present. In the paramagnetic range, this term decreases with T as the chemical disorder increases, the decrease being especially large at the order-disorder (L1 2 -A 1 ) transition. Such behaviour is attributed to the existence of short-range magnetic order in the paramagnetic state of Co 30 Pt 70 , which would be enhanced by the increase of the chemical disorder, i.e. by the increase of the Co-Co coordination, thus reducing the spin-disorder contribution to the resistivity. All the data are in very good agreement with a previous comparative study of equi-atomic NiPt and CoPt phases, which led to a similar conclusion.