Study Of Microstructure And Magnetic Response Properties At High Frequency Of Ferromagnetic Films

Ferromagnetic materials with excellent dynamic magnetic properties in Gigahertz range can be widely used in microwave devices,electromagnetic interference devices and microwave absorbers in the future.With the development of electronic devices,magnetic devices would meet the development requirement with thin film or even patterned properties.So far,the research about ferromagnetic films mainly concentrated on materials selection and preparation technology,which could improve the high frequency properties.With decrease of thin films size,the effect of geometrical size and magnetic structure cannot be ignored.Traditional theory could not work to explain certain phenomenon.In this thesis,conbined with experiments and micromagnetic simulation,the high frequency dynamic magnetic properties of ferromagnetic films have been discussed,which follows the main line of reducing size of thin film.With design of film structure,this thesis explored the controllability as well as physics mechanism of ferromagnetic films in GHz range from four aspects i.e.the reduction of thickness,patterned film,the reduction of unit size and structure period.During this research,from the view of micro-structure and internal magnetic properties,micromagnetic simulation and the connection between micromagnetic and macromagnetic properties gave the chance to explore the dynamic response of magnetic films within micrometer and nanometer range.Design and optimization of ferromagnetic film structure in micrometer and nanometer size may clear the way to produce light,integrated and controllable novel microwave magnetic devices.The major works and the innovations involved in the dissertation are as follows:1.Combined the micromagnetic model and experiment,this theis demonstrated that local-area order in FeCo-based amorphous films could induce the uniaxial anisotropy,thus realizing the controllability of the resonance frequency by the variable film thickness in GHz range,which was more promising in the application compared to the films with external field.2.By studying the resonance behavior of uncoupled FeCo-based soft striped film,an overlay model of the resonance peak is established,which provided a feasible method for controlling the number and the location of peak in high frequency.Based on the Rado-Weertman boundary condition,this thesis induced the pinning boundary conditions into the stripe patterned thin films with uneven edges and put up with pinning parameters formula with parameters of energy contribution and edge geometrical characters,which was essential for the research of edge impact to the high frequency properties of magnetic films.3.This thesis designed a FeNi nanodisk structure with thick edge,which broke the critical size for the existence of vortex state in traditional nanodisk.The controllability of polarization could be realized by the excited energy of GHz rotating field in dynamic response model due to the mechanism of spin wave of vortex state in high frequency range.Moreover,compared to the traditional nanodisk,this design could possess larger face density and faster response rate without any interference between structure units.4.This thesis designed a L1₀-FePt/FeNi double-layer film with Skyrmion-like magnetic structure without any external inducing field.Such structure realized the stable state of Skyrmion-like magnetic distribution with unit pattern design.Such magnetic structure revealed a novel dynamic response mode,which enriched the multiple resonance peaks model of high frequency dynamic magnetic response and was not affected by the element spacing over a wide range.In conclusion,the research of this thesis concentrated on the dynamic response of magnetic moments excited by microwave field within limited system.During the research,this thesis designed and optimized the structure of ferromagnetic thin films by dynamic properties of films effectively in GHz range while reducing the size of corresponding structure.The theoretical models and micromagnetic analysis involved in the research gave us a new idea to study the mechanism of high frequency response impacted by micro-structure and lay a theoretical foundation as well.