Mechanism of magnetic coupling in rare-earth-Al2and rare-earth-Zn compounds

By analyzing ordering-temperature and nuclear-magnetic-resonance measurements in ordered rare-earth-zinc and rare-earth-${\mathrm{Al}}_2$ compounds we conclude that although strong orbital polarization of the conduction band is present in the vicinity of the $4f$ electrons, it does not propagate between ions. The dominant mechanism of magnetic coupling in these compounds is via the classical spin polarization. Some evidence exists suggesting that the strength of the exchange interaction is greater for light rare earths than for heavy rare earths.