Vortex chirality in an array of ferromagnetic dots

Magnetization of an array of submicron permalloy dots was investigated using the diffracted magneto-optical Kerr effect. The shapes of the higher-order hysteresis loops are explained by the magnetic form factors associated with a vortex spin structure in each disk. The imaginary part of the form factor also explains the unexpected measured differences between hysteresis loops obtained on positive and negative diffraction orders. Shape effects account for the coherent chirality of the vortices over the array