Two distinct stable magnetic states in narrow ferromagnetic rings have been reported1-4. Onion state can form in the ring structure during the magnetization reversal process from the field of saturation to the lower or even opposite one. At the relative low field, the configuration of magnetization can be in an arrangement in which the local magnetization is aligned to the direction of perimeter of the ring due to the shape anisotropy of the narrow ring. After the onion state forms, a rotating field of constant magnitude can drag the domain wall along the perimeter of the ring. This phenomenon has been demonstrated5 by measuring the magnetoresistance (MR) of the ring with keeping the magnitude of the field constant and rotating it. The purpose of this investigation is to use the rotating MR measurement to identify the critical field at which the onion state can form and the lowest field which can still drag the domain walls at the onion state.
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