Electron transport studies in Ni-rich γ-NiFeCr alloys

Abstract

Detailed electrical resistivity measurements in concentrated Ni-rich γ-Ni 100− x− y Fe x Cr y (8⩽ x⩽17.5, 8⩽ y⩽21) ternary alloys have been made in the temperature range of 1.2⩽T⩽290 K. The alloys with low Cr content (⩽15 at%) are ferromagnetic while those with high Cr (⩾18 at%) show exotic low-temperature magnetic behaviour with T c (ferromagnetic Curie temperature) and T f (spin-freezing temperature) below 60 and 20 K, respectively. The resistivity data of all the alloys exhibit distinct minima lying between 7 and 35.5 K, nearly unaffected by external magnetic fields. Below the minima, the resistivity is well described by the electron–electron (e–e) interaction effects ( ρ∝ T ), independent of the magnetic states of the alloys. The density of states at the Fermi level, calculated from the coefficient of the T term, is in good agreement with that obtained from the specific heat data. This gives a strong support to the present interpretation of the resistivity minima. Further, the positive magnetoresistance at 4.2 K till magnetic fields of 14 kOe has shown an H 2 dependence, as expected from the e–e interaction effects in the low-field limit. In the temperature range of T min/2⩽ T⩽2 T min, besides the e–e interaction effects, magnetic (∝ T 2) and phonon (∝ T 3) contributions have been distinctly isolated. At higher temperatures (>100 K), a linear electron–phonon term along with the magnetic term are observed till about 200 K for the low-Cr alloys. But above 200 K, only a linear term is obtained in the low-Cr alloys whereas in the high-Cr ones, it is found right from 100 K onwards. Interestingly, the values of the coefficient of the magnetic term (∝ T 2) come out to be of the same order as the theoretical one (10 −5 μΩ cm K −2). This clearly shows that the magnetic contribution to the electrical resistivity arises due to the s–d and s–s scattering. Moreover, the values of the residual resistivity of all the alloys, calculated using the two-current model and Matthiessen's rule, are in reasonable agreement with the experimental values.