Magnetisation reversal of thin submicron elliptical permalloy elements

We have studied the magnetisation reversal of elliptical, polycrystalline permalloy elements as a function of their aspect ratios by Lorentz transmission electron microscopy. In situ magnetising experiments revealed four possible types of magnetisation reversal, which depend on the in-plane and out-of-plane aspect ratios of the submicron elements. The types differ in the number of observed vortices and a low or high remnant magnetisation. Diagrams of the types of magnetisation reversal are given for submicron elliptical elements of length 350, 550, 750 nm and a thickness of 8 and 15 nm, respectively. The switching, vortex evolution and annihilation fields were investigated and show a strong correlation with the element shape. We present magnetisation loops which are obtained by micromagnetic simulations and are characteristic for the observed types of reversal.