On the superparamagnetic size limit of nanoparticles on a ferroelectric substrate

When decreasing the size of nanoscale magnetic particles, their magnetization becomes vulnerable to thermal fluctuations as the superparamagnetic limit approaches, thus hindering applications relying on a stable magnetization. Here, we theoretically investigate how a magnetoelectric coupling to a ferroelectric substrate modifies the superparamagnetic limit, with a special focus on the possible realization of substantially smaller multiferroic clusters with thermally stable magnetization. For an estimate of cluster size we perform calculations for iron nanoparticles multiferroically coupled to a BaTiO3 substrate. Our numerical results indicate that steering the polarization of BaTiO3 with electric fields affects the magnetism of the deposited magnetic clusters. The work provides a suggestion on how the strength of the magnetoelectric coupling might be extracted from telegraph noise experiments. (paper)