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Simulation and Optimization for Strain-Mediated Multiferroic Applications: Memory, Logics and Sensor/Actuator


Strain-mediated multiferroic materials have high energy-efficiency when used control magnetism using electric fields. Therefore, these materials are good candidates for magnetic applications, e.g. memory, logics and sensor/actuator. This dissertation focuses on the numerical simulation of strain-mediated multiferroic systems. Numerical codes using finite element and finite difference approaches, are developed and implemented to solve the fully coupled governing equations of micromagnetism and piezoelectricity. Part I of this dissertation provides a fundamental understanding of the equilibrium states of magnetic memory elements with different shapes or applied strains at microscale. The simulation results indicate that the equilibrium states depend on many factors including the geometry, the exchange constants and even the residual strain. Part II of this dissertation primarily discusses spin waves in the mutiferroics. Spin waves can be excited by traveling mechanical waves. These spin waves, known as magnetoelastic spin waves, can propagate up to several millimeters of distance without significant decay. In addition, perpendicular standing spin waves (PSSWs) can be generated in undulating thin film, since the magnetic field is not uniform through the thickness. Thus, multiferroics are promising in applications such as spin wave excitation and high-frequency filters. In Part III, the design and development of micro-motors are discussed. These motors use electric field to move the soft-magnetic beads. The simulation predicts the bead dynamics accurately, and describe how it is influenced by the input voltage, given the magnetic and electric properties of the piezoelectric substrate, the magnetoelastic disk/ring geometry and the properties of the soft-magnetic bead. In summary, the models developed in this dissertation provide efficient tools for the design and development of the multiferroic applications.

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