π -anisotropy: A nanocarbon route to hard magnetism

Hybridization and charge transfer at molecule-metal interfaces can alter the magnetic anisotropy of transition metal ferromagnets. Here, the authors show that the molecule C${}_{60}$ increases the magnetic energy product of cobalt thin films by 520 % at low temperature. The authors outline a mechanism for this effect, dubbed $\ensuremath{\pi}$-anisotropy, which explains magnetic hardening as a consequence of $p$-$d$ hybridization and broken interfacial symmetry. It is anticipated that this may provide a route towards a rare earth free high-coercivity magnet.