Spin-Wave Resonance Studies in Invar Films

The technique of spin-wave resonance has been employed to experimentally determine the spin-wave dispersion coefficient $D$ for different compositions of nickel in iron. The results of this investigation indicate that for the fcc alloys (nickel-rich), the spin-wave dispersion coefficient decreases from its room-temperature value of 3.8×${10}^{-27\mathrm{}}$ erg ${\mathrm{cm}}^2$ at 60-at.% Ni in Fe to a minimum of 2.7×${10}^{-27\mathrm{}}$ erg ${\mathrm{cm}}^2$ at 45-at.% Ni in Fe. It then rises to a maximum of 6.5×${10}^{-27\mathrm{}}$ erg ${\mathrm{cm}}^2$ at the Invar point, 27-at.% Ni in Fe. The spin-wave dispersion coefficient for the bcc alloy (iron-rich) taken at room temperature decreases linearly from its value of 5.0×${10}^{-27\mathrm{}}$ erg ${\mathrm{cm}}^2$ at pure iron to a value of 2.7×${10}^{-27\mathrm{}}$ erg ${\mathrm{cm}}^2$ at the Invar point. The shape of both the bcc and fcc plots are in agreement with a plot constructed from data obtained using the technique of small-angle neutron scattering. The Landé $g$ factor has also been determined as a function of composition of nickel in iron. For the bcc material, $g$ is a constant at 2.20 in the range 22-31-at.% Ni in Fe. For the fcc material, $g$ varies from its value of 2.15 in the region 42-60-at.% Ni in Fe to a value of 1.79 at 33-at.% Ni in Fe and then rises to 2.00 near the Invar point. The complex spin-wave patterns that are often detected in Invar thin films of mixed crystalline structure have been attributed to the different magnetizations associated with each of the crystalline phrases.