Abstract
In this thesis, the magnetization switching processes of ferromagnetic permalloy thin films and the applications on microelectromechanical systems and cell manipulation are investigated. The micro and nano structures are prepared by conventional photolithography and electron beam lithography. Ring-shaped geometry is a promising candidate for ultrahigh density magnetoresistive memory. However, from previous researches it can be found that two different switching mechanisms exist and its magnetization processes are hard to control. In this study, a repeatable magnetization process of permalloy rings can be effectively controlled through the introduction of notches as nucleation sites. For notches at the same side with respect to the field direction, two-step switching process is observed; for diagonal notches at opposite sides with respect to the field direction, one-step switching process is observed. An actuator with single-domain thin films is designed by modified Stoner-Wohlfarth model. The prototype of cantilever beam actuated by single-domain thin films is also fabricated experimentally. Large planar deflection is observed; the hysteresis and magnetic switching behavior of the single-domain magnetic thin films are also observed in the actuation. In addition, bio cells are successfully manipulated using ferromagnetic thin films. Different stray fields caused by the domain walls of the thin film can effectively control the distributions of bio cells on the chip.