Spectrum of noncollinear metastable configurations of a finite-size discrete planar spin chain with a collinear ferromagnetic ground state

A theoretical method is used to find, in an accurate and systematic way, all the possible equilibrium magnetic states of a finite-size one-dimensional chain of classical planar spins, interacting via ferromagnetic nearest neighbor symmetric exchange and subjected to a uniaxial anisotropy which favors the orientation of the spins along an easy axis within the plane perpendicular to the chain. For a chain with N spins, the energy is a function of N absolute orientation angles and, owing to the absence of energy competition, the ground state is collinear ferromagnetic and doubly degenerate. The ground state corresponds to a global minimum of the energy in the N-dimensional space, while metastable states correspond to local minima.