  The demand for high-density storage is urgent in the current era of data
explosion. Recently, several single-molecule (-atom) magnets/ferroelectrics
have been reported to be promising candidates for high-density storage. As
another promising candidate, single-molecule multiferroics are not only small
but also possess ferroelectric and magnetic orderings, which can sometimes be
strongly coupled and used as data storages to realize the combination of
electric writing and magnetic reading. However, they have been rarely proposed,
and never been experimentally reported. Here, by building Hamiltonian models,
we propose a new model of single-molecule multiferroic in which electric
dipoles and magnetic moments are parallel and can rotate with the rotation of
the single molecule. Furthermore, with performing spin-lattice dynamics
simulations, we reveal the conditions (e.g., large enough single-ion anisotropy
and appropriate electric field) under which the new single-molecule
multiferroic can arise. Based on this model, as well as first-principles
calculations, a realistic example Co(NH3)4N@SWCNT is constructed and
numerically confirmed to demonstrate the feasibility of the new single-molecule
multiferroic model. Our work not only sheds light on the discovery of
single-molecule multiferroics but also provides a new guideline to design
multifunctional materials for ultimate memory devices.
