Field-dependent transport properties in paramagnon systems

We examine, theoretically, the low-field dependence of certain transport properties in nearly magnetic itinerant-fermion systems which exhibit strong spin fluctuations describable by the paramagnon theory. We study more precisely the viscosity η(H) of partially polarized normal liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at low field H and low temperature, and also the magnetoconductivity σ(H) of exchange-enhanced metals. We find analytical expressions relating these transport properties to the field dependence of the magnetization M=χ(H)H. We find that η(H) and σ(H) increase or decrease when H increases, depending upon whether χ(H) becomes smaller or larger than χ(0). Comparison of our results with up-to-date experiments for η(H) in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is quite satisfactory as far as the sign and magnitude of the effect are concerned.