Metastable states in magnetic nanorings

Magnetization states and hysteresis behavior of small ferromagnetic rings, of diameters 180–520 nm, have been investigated using magnetic force microscopy. In addition to the expected bi-domain (“onion”) and flux-closed (“vortex”) magnetization states, a metastable state has been found. This “twisted” state contains a 360° domain wall which can exist over a wide range of applied fields. Four possible configurations of the twisted state are possible. Micromagnetic modeling shows that the twisted state is stabilised in small diameter, narrow rings. Additionally, more complex configurations such as double twisted states with two 360° walls have been observed.