Exchange Stiffness Constants in Ni–Co Alloys

Abstract

Magnetization measurements of f.c.c. Ni–Co alloys using pendulum-type magnetometer have been made from liquid He temperature to room temperature. Magnetization vs temperature curves have been analysed on the basis of the spin wave theory. The exchange integral J and the exchange stiffness constant D are estimated. The composition dependence of D is not consistent with that obtained by Hinoul et al. from spin wave resonance experiments nor with that obtained by Wakoh from the calculation on the basis of itinerant electron model. The experimental results seem to support that the contributions to the spin wave dispersion relation from the itinerant and localized characters of electrons are additive as shown by Englert et al. and Yamada et al. The role of the inter-atomic exchange interaction in Ni–Co alloys seems to be important in order to explain the observed values of D.