Spin-wave excitations in aluminum

Observation of spin-wave excitations in the conduction electrons of aluminum is reported. Using the microwave transmission technique at a frequency of 79 GHz we are able to observe the buildup and propagation of spin-wave modes over the limited temperature range of 10-20 K. At lower temperatures the spin-wave spectra are obscured by the simultaneous propagation of much stronger Gantmakher-Kaner-type oscillations. Although an exact theory for spin-wave propagation in a material as complex as aluminum is lacking, we compare our data with the theory of Platzman and Wolff and that of Wilson and Fredkin, both of which were developed for isotropic systems, in order to make an approximate determination of the exchange coupling of the conduction electrons. The analysis yields an exchange interaction that is characterized by a positive value of the Landau Fermi-liquid parameter B (or B₀) with a magnitude of approximately 0.1. Although this value is about a factor of 4 smaller than earlier estimates from the frequency dependence of the conduction-electron spin-resonance signal, these observations confirm the presence of a significant exchange interaction among the conduction electrons of aluminum and the positive sign of the parameter B.