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$\cdot $14 and 1$\cdot $25 cm at 290 degrees K. The g-factor for iron is measured to be 2$\cdot $06 $\pm $ 0$\cdot $02 and for nickel 2$\cdot $22 $\pm $ 0$\cdot $02. In the nickel-iron alloys there appears to be a sharp anomaly near 40% Ni, where the g-factor falls to 2$\cdot $01, and for alloys having between 50 and 85% Ni the g-factor is found to be 2$\cdot $10 $\pm $ 0$\cdot $02. Apart from nickel there seems to be good agreement between g - 2 obtained from the microwave measurements and 2-g$^{\prime}$ derived from gyromagnetic experiments. The half-width of the absorption line for iron is 700 Oe $\pm $ 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.