Spin Wave Stiffness Constant of Laves Phase Invar Compound (Zr_0.7Nb_0.3)Fe₂

The spin wave stiffness constant of a Laves phase invar compound (Zr 0.7 Nb 0.3 )Fe 2 at low temperatures was estimated to be 350±50 meVA 2 by inelastic neutron scattering experiment above room temperature. This value is significantly greater than the value (125 meVA 2 ) of the spin wave stiffness constant deduced from the magnetization measurement. Such a discrepancy has been found in all other Invar materials.