Phase diagram for magnetic nano-rings

The minimum-energy single-domain magnetization state in a magnetized nano-ring is determined as a function of material and shape parameters. A phase diagram is derived within the framework of a Fourier-space approach for magnetic computations, showing the expected position of the ground state for any given set of external degrees of freedom. A series of micromagnetic simulations for suitably chosen parameters, show excellent agreement with the obtained theoretical results. An electron holography experiment has been carried out as a test on phase diagram reliability. The validity of the treatment, in particular the simplification employed in choosing ideal uniform rather than more physical quasi-uniform single-domain states, is thoroughly discussed in order to establish clear boundaries of applicability of the phase diagram.