UCLA

The development of cell sorting technologies in the late 1960s has allowed for enhanced diagnostic tools advancing the field of biotechnology. Among the various sorting mechanisms, magnetic cell sorting is desirable for its rapid analysis capabilities and compatibility with biological samples. However, the use of a permanent magnet required for magnetic sorting mechanisms presents a challenge when scaling these devices to the nanoscale. In this work, the prospective of strain-mediated multiferroic composite structures for use in magnetic cell sorting is presented. In a multiferroic composite structure, a ferromagnetic material is layered on top of a ferroelectric substrate. By applying a voltage to the ferroelectric substrate, the substrate generates an in-plane strain. Through mechanical coupling of the two layers, the magnetization of the ferromagnetic material is rotated. As a result, magnetization can be changed without the use of a permanent magnet allowing for scalable control of magnetism. Key concepts are discussed for the successful implementation of strain-mediated multiferroic cell sorting devices. First, a new device is simulated and demonstrated to be capable of 360o magnetization rotation of an elliptical magnetic element using a simple voltage pulse. This design is an improvement over the currently available structures capable of similar magnetization dynamics. Next, the limitations of a dynamic voltage input in a multiferroic composite structure are discussed. This work offers new information about how successful performance of cell sorting devices may be impeded due to changing input voltage and fabricated defects in the structure. Additionally, a new finite element model is developed to better incorporate the material behavior of the ferroelectric substrate and its corresponding effects on magnetization in a single domain ferromagnetic material. The results of these studies are a stepping stone towards better understanding the discrepancies between the existing models of strain-mediated multiferroic structures and experimental observations of these fabricated devices. The last contribution of this work is understanding how magnetic beads used in cell sorting applications might respond to the force generated by the magnetic field in strain-mediated structures. This work lays the groundwork for better understanding the design of future strain-mediated multiferroic cell sorting devices.