ELECTRON-TRANSPORT STUDIES IN NI-RICH GAMMA-NIFECR ALLOYS

Detailed electrical resistivity measurements in concentrated Ni-rich g amma-Ni100-x-yFexCry (8 less than or equal to x less than or equal to 17.5, 8 less than or equal to y less than or equal to 21) ternary allo ys have been made in the temperature range of 1.2 less than or equal t o T less than or equal to 290 K. The alloys with low Cr content (less than or equal to l5 at%) are ferromagnetic while those with high Cr (g reater than or equal to 18 at%) show exotic low-temperature magnetic b ehaviour with T-c (ferromagnetic Curie temperature) and T-f (spin-free zing temperature) below 60 and 20 K, respectively. The resistivity dat a 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) interact ion effects (rho proportional to root T), independent of the magnetic states of the alloys. The density of states at the Fermi level, calcul ated from the coefficient of the root T term, is in good agreement wit h that obtained from the specific heat data. This gives a strong suppo rt to the present interpretation of the resistivity minima. Further, t he 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 effe cts in the low-field limit. In the temperature range of T-min/2 less t han or equal to T less than or equal to 2T(min), besides the e-e inter action effects, magnetic (proportional to T-2) and phonon (proportiona l to T-3) contributions have been distinctly isolated. At higher tempe ratures (>100 K), a linear electron-phonon term along with the magneti c 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 (proportional to T -2) come out to be of the same order as the theoretical one (10(-5) mu Ohm cm K-2). This clearly shows that the magnetic contribution to the electrical resistivity arises due to the s-d and s-s scattering. More over, the values of the residual resistivity of all the alloys, calcul ated using the two-current model and Matthiessen's rule, are in reason able agreement with the experimental values. (C) 1998 Elsevier Science B.V. All rights reserved.