Gyration mode splitting in magnetostatically coupled magnetic vortices in an array

We present the experimental observation of gyration mode splitting by the time-resolved magneto-optical Kerr effect in an array consisting of magnetostatically coupled Ni81Fe19 discs of 1 μm diameter, 50 nm thickness and inter-disc separations varying between 150 and 270 nm. A splitting of the vortex core gyration mode is observed when the inter-disc separation is 200 nm or less and the splitting is controllable by a bias magnetic field. The observed mode splitting is interpreted by micromagnetic simulations as the normal modes of the vortex cores analogous to the coupled classical oscillators. The splitting depends upon the strength of the inter-disc magnetostatic coupling mediated by magnetic side charges, which depends strongly on the magnetic ground states of the samples.