Coupling of single atom magnetic anisotropy to the neighboring electric polarization

Multiferroic coupling arises when two ferroic order parameters influence each other. The most popular case is the coupling of magnetization and electric polarization, arising from the interaction of magnetic moments with the surrounding localized electrical charges. In this work we address such interaction at the atomic scale. More specifically, we have recently reported that it is possible to use the abrupt compositional discontinuity occurring at a surface to induce biestable electric polarization in ultrathin ionic insulators [Nature Nanotech. 13, 19-23 (2018)]. Scanning Probe Methods are capable to manipulate matter at the atomic scale while probing simultaneously its electronic and magnetic properties. In this way, using ultrathin films of binary rock-salts, we have built the specific structural and compositional environment that provides a bistable electric polarization controlled by an external electric field. We have deposited individual Co atoms onto the rock-salt films and measured their magnetocrystalline anisotropy by means of inelastic electron tunneling spectra. We show that the uniaxial anisotropy can reversibly tuned to two stable values following the electric polarization switching as a consequence of the crystal electric field experienced by the Co atom.