Evidence of short-range order in NiCo (25at%Co) alloy by electrical resistivity

Abstract

Lattice parameter and atomic volume measurements against Co content in NiCo alloy, annealed at 900 C and slowly cooled to room temperature, showed a pronounced inflection near 33.1% Co. Fine filings of the same alloy quenched from 900 C showed higher lattice parameters than slowly cooled samples. These parameters became even smaller once the NiCo alloy was annealed for a long time at 750 C and quickly cooled to room temperature. These results should indicate the existence of a critical temperature of ordering, Tc, in the range 750--800 C. Because of the similarity of the scattering factors of Ni and Co, the X-ray technique could not confirm the existence of the superstructure. According to Collins and Wheeler, there are small anomalies in the magnetization saturation and thermal e.m.f. indication some ordering degree in the Ni[sub 3]Co alloy. Bozorth using magnetic permeability and electrical resistivity with this alloy composition has not been able to detect these anomalies. Parizek and Cizek studied the NiCo (21at%Co) alloy above the Curie temperature and observed a lower electrical resistivity in the deformed state than in the annealed state, possibly due to the modified electronic structure. The contribution of the magnetic transition, near the Curie temperature,more » should also be considered in the short range order (SRO).« less