Spin waves in ferromagnetic transition metals. I. General formalism and application to nickel and its alloys

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Abstract
A new formula is derived for the spin-wave stiffness constant D and is compared with previous work. It is shown that in NiD is very sensitive to the 'ground-state' exchange splitting Delta in the d band and that hybridisation with the sp band has little effect on D. The observed value of D yields a value of 0.40 eV for Delta , which is larger than the observed quasiparticle exchange splitting of 0.33 eV, as expected theoretically. Calculations on D in Ni alloys, within the virtual crystal approximation, are compared with experimental results on NiCo and NiFe.