  Hard magnets with high coercivity, such as Nd2Fe14B and SmCo5 alloys, can
maintain magnetisation under a high reverse external magnetic field and have
therefore become irreplaceable parts in many practical applications. Molecular
magnets are promising alternatives, owing to their precise and designable
chemical structures, tuneable functionalities and controllable synthetic
methods. Here, we demonstrate that an unusually large coercive field can be
achieved in a single-chain magnet. Systematic characterisations, including
magnetic susceptibility, heat capacity and neutron diffraction measurements,
show that the observed giant coercive field originates from the spin dynamics
along the one-dimensional chain of the compound because of the strong exchange
coupling between Co(II) centres and radicals.
