Ferromagnetic resonance absorption in colloidal suspensions

Ferromagnetic resonance absorption in colloidal suspensions of pure metals and alloys has been investigated at wave-lengths of 3·14 and 1·25 cm at 290° K. The g-factor for iron is measured to be 2·06 ± 0·02 and for nickel 2·22 ± 0·02. In the nickel-iron alloys there appears to be a sharp anomaly near 40 % Ni, where the g-factor falls to 2·01, and for alloys having between 50 and 85 % Ni the g-factor is found to be 2·10 ± 0·02. Apart from nickel there seems to be good agreement between g—2 obtained from the microwave measurements and 2—g' derived from gyromagnetic experiments. The half-width of the absorption line for iron is 700 Oe ± 10 %. For the face-centred alloys the line width varies smoothly with a minimum value of about 300 Oe near 70 % Ni, where the magnetic anisotropy is least. It does not seem possible to assign the whole of the line width to spin-spin interactions of the type suggested by Kittel & Abrahams. A brief discussion of the g-factors for iron and nickel is given in terms of a localized electron model.