Observation of a Bi-Domain State and Nucleation Free Switching in Mesoscopic Ring Magnets

Abstract

We present the results of a study of the magnetic properties of an array of 34-nm thick Co(100) epitaxial ring magnets, with inner and outer diameters of $d_{\mathrm{in}}=1.3\mathrm{}\mu$m and $d_{\mathrm{out}}=1.6\mathrm{}\mu$m, respectively. Magnetic measurements and micromagnetic simulations show that a two step switching process occurs at high fields, indicating the existence of two different stable states. In addition to the vortex state, which occurs at intermediate fields, we have identified a new bi-domain state, which we term the onion state, corresponding to opposite circulation of the magnetization in each half of the ring. The onion state is stable at remanence and undergoes a simple and well characterized nucleation free switching.