Electrical resistivity in ferromagnetic NiCu alloys near the Curie point

Direct measurements of the temperature derivative of the electrical resistivity d/dT have been made on several ferromagnetic NiCu alloys with high Cu content (20, 30, 40, 50.4 at %). For Ni₈₀Cu₂₀ and Ni₇₀Cu₃₀ the results closely resemble the general pattern found in pure ferromagnets: d/dT - b – a ln ¦¦, for 10^–3 ¦¦ 10^–1, with a and b constants and = (T/T_c)– 1. In Ni₆₀Cu₄₀ the rounding off of the magnetic transition is already so pronounced that a similar analysis is hardly significant. In the Ni_49.6Cu_50.4 sample negative values of d/dT were confirmed above ~165 K. The possible theoretical implications of the results are briefly discussed.Work supported by Instituto de Alta Cultura, Portugal (Project PF1).