Cycle-by-cycle observation of single-domain-to-vortex transitions in magnetic nanodisks

摘要

The switching behavior of permalloy (Ni_(81)Fe_(19)) disks with dimensions close to the experimentally determined phase boundary separating the single domain and vortex ground states was investigated. The disks fabricated with electron beam lithography and thermal evaporation were 97 nm wide and 26 nm thick. The remanence curve, measured with a magneto-optical Kerr magnetometer, shows the presence of three different remanence states in different magnetic field regimes; vortex state at fields below 110 Oe, metastable state at fields 110 Oe < H < 520 Oe, and single domain state at fields above 520 Oe. High sensitivity magneto-optical measurements combined with an advanced applied field sequence allowed a cycle-by-cycle observation of the collapse of the single domain state into the vortex ground state via a partially remanent metastable state.