Stiffness constant of weak ferromagnetic Ni-based alloys. Low-temperature measurements in Ni:V, Ni:Mo, Ni:Ru, Ni:Cr: Interpretation within RPA-CPA theories

The stiffness constant D was measured at 4.2K in Ni:V, Ni:Cr, Ni:Mo, Ni:Ru for various impurity concentrations. The authors observed a great similarity between its concentration dependence and that of magnetisation in all the alloys, with, however, a slight discrepancy in Ni:Ru. Spin waves at high energy in Ni 0.96 V 0.04 are also reported. Results of measurements are interpreted within CPA-RPA theories. By determining the splitting value between up and down bands Delta (or the intra-atomic interaction constant of electron U eff ) in order to reproduce the experimental D value in pure nickel, they found that the concentration dependence of D is similar to that of magnetisation and that its evolution with the change of impurity is correct. As this agreement is related to a large value of Delta (0.06 Ryd) the role of this parameter is studied.