Weak itinerant-electron ferromagnetism in Ni-rich Ni-Fe-Cr and Ni-Fe-V alloys

Detailed magnetization measurements have been carried out for a number of alloys in both the ternary series Ni-Fe-Cr and Ni-Fe-V in the Ni-rich region, mainly to study the effect of the addition of Cr or V. The following points emerge from the measurements in the ferromagnetic as well as paramagnetic range of temperatures: (i) The low-temperature magnetization data reveal that in Ni-Fe-Cr alloys, along with the spin waves, Stoner single-particle excitation corresponding to weak itinerant-electron ferromagnets (following a $T^2$ law) is present. The Stoner term gains prominence with increasing Cr concentration. In Ni-Fe-V alloys there is also some indication of the existence of other than spin-wave excitations. (ii) The variation of $\bar{\mu }$ (average number of Bohr magnetons per atom) with concentration shows the same type of nonlinearity in both systems, in agreement with the earlier data of Men'shikov et al. on Ni-Fe-Cr alloys. (iii) Magnetization falls much faster with temperature than in conventional ferromagnets (e.g., Ni,Fe) over the entire ferromagnetic region. (iv) The Rhodes-Wohlfarth ratio ($\frac{q_c}{q_s}$) shows a rapid increase with increasing concentration of Cr or V (i.e., with decreasing $T_c$) and Arrott plots of the Cr- or V-rich alloys are linear over a large temperature range. From the above observations we conclude that the addition of Cr or V in Ni-Fe alloys moves them towards weak itinerant-electron ferromagnetism.