Collective effects in spin-polarized Boltzmann gases

As a result of an investigation of the real collision integral for paramagnetic atoms, we have obtained a criterion for propagation of spin waves in a spin-polarized Boltzmann gas. The main condition for propagation of weakly damped spin waves is a high anisotropy of the atomic scattering amplitude with predominance of the forward scattering. This condition is different from those suggested in earlier publications. Our results indicate that the range of paramagnetic gases where weakly damped spin waves can propagate at the room temperature is considerably wider than it was assumed previously. One example is vapors of alkali metals (Na, Cs, and Rb), where the degree of electron spin polarization can be very high.