Reversal mechanism of patterned ferromagnetic elements

Understanding of magnetization reversal dynamics in patterned ferromagnetic elements, or building blocks, is crucial to the development of modern magnetic storage media and spintronic devices. Using state-of-the-art, field-emission transmission electron microscope (TEM) equipped with a custom-made objective lens (the only one of its kind in the world) that allows high-resolution magnetic imaging and electron holography, we study the reversal mechanism and hysteresis behavior of patterned rings, squares, and ellipses with different aspect ratios of Permalloy and Co thin-films. By quantitative analysis of the local magnetization, we measure magnetic properties and shape effect of individual elements, and compare experimental observations with theoretical calculations. We explain why a parent state of the elements, isolated or in an array environment, can result in different low-energy ground states, depending on the switching rate, and how the energy barrier to the vortex nucleation can be measured. New results using a magnetic force microscope built into a TEM stage to locally induce magnetic field gradient and to change magnetic polarization of the elements to study element-element interaction and magnetic reversal will be also reported.