Magnetic Anisotropy and Conduction-Electron Exchange Polarization in Ferromagnetic (Rare-Earth)Al2Compounds

${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ NMR in ferromagnetic $R{\mathrm{Al}}_2$ ($R=\mathrm{P}\mathrm{r},\mathrm{N}\mathrm{d},\mathrm{S}\mathrm{m},\mathrm{G}\mathrm{d},\mathrm{T}\mathrm{b},\mathrm{D}\mathrm{y},\mathrm{H}\mathrm{o}$) has been studied. The easy direction of magnetization has been observed experimentally for the first time and a theoretical calculation, in accord with the observation, has been developed. The $s-f$ exchange parameters have been examined and in addition to the isotropic exchange parameter ${\Gamma }_{\mathrm{sf}}$, the existence of a small but significant anisotropic $s-f$ exchange term is verified experimentally for the first time. The accurately determined (±1%) isotropic exchange parameters are compared with presently available theoretical predictions.