Dynamic Cantilever Magnetometry Of Micro-nano Samples

Magnetic materials are an important branch of functional materials.Magnetic components made of magnetic materials play an irreplaceable role in our daily lives.With the advancement of nanotechnology,micro-nano magnetic samples have also begun to enter everyone’s sight.It has important application prospects in the field of high-density magnetic storage,magnetic force detection,magnetic sensors and biomedicine.At present,the characterization methods of micro-nano magnetic samples mainly include magnetic force microscope,Lorentz transmission electron microscope,magneto-optic Kerr microscope,vibrating sample magnetometer,transport measurement and neutron scattering.These characterization methods have certain requirements on the morphology and volume of samples,so it is difficult to meet the testing requirements of all samples.As a new micro-nano magnetic sample research method,dynamic cantilever magnetometry has the following characteristics:there is no requirement for the shape of the sample(could be micro rods,nano wires,nano rods,nano films,nano particles,etc.)The measured physical quantities are the magnetic moment and anisotropy of the sample,which reflect the overall magnetism of the samples.The sensitivity is extremely high,our current minimum limit is detecting the magnetic moment of 1.7×10-15 emu of a ferromagnetic sample.This dissertation is divided into several parts to introduce my work:The first two chapters mainly introduce the research background and related knowledge of dynamic cantilever magnetometry.Chapters 3 and 4 mainly introduce the device and the Micro-nano processing technology of the dynamic cantilever magnetometry.Chapters 5 and 6 are experimental parts.Chapter 5 introduces the characterization of three ferromagnetic samples using dynamic cantilever magnetometry;Chapter 6 introduces the characterization of two magnetic phase transition samples using dynamic cantilever magnetometry.Chapter 7 summarizes my work in dynamic cantilever magnetometry measurement.At the same time,having an outlook of the potential development of dynamic cantilever magnetometry in the future.Appendix A is the operation manual of the dynamic cantilever magnetometry device summarized by me.Appendix B is the simulation operation method of the vibration frequency and elastic coefficient of the cantilever beam by COMSOL.I hope they can help other people in the research group to do better in the future experiments!There are three main innovations in this dissertation:1.Previously,the work reported in the field of dynamic cantilever magnetometry is mostly related to the research of one-dimensional nanowire and nanotube samples.In order to enrich the sample selection of this method,we have explored two complete micro-nano processing technology,which can accurately and efficiently process and transfer most micro-nano magnetic samples,greatly enriching the sample selection for dynamic cantilever magnetometry.2.Conventional characterization methods are difficult to obtain anisotropy and other parameters of micro-nano magnetic samples.For nanoparticle-scale samples,conventional characterization methods are even difficult to measure magnetic signals.We made full use of the characteristics of high sensitivity of dynamic cantilever magnetometry to study the anisotropy,coercivity,saturated magnetization field and other characteristics of a variety of nano-scale ferromagnetic materials.Among them,the side length of a single CoFe2O4 nano-pyramid is only 90 nm,and the thickness of self-assembled monolayer of Fe3O4 nano-particles is about 15 nm.These works have a positive effect on the study of nanoscale magnetic materials and even nano-particle magnetic materials.3.Previously,micro-nano samples’ magnetic phase transition mostly stayed in the stage of local characterization or unidirectional characterization.We use dynamic cantilever magnetometry to detect the skyrmion and phase diagrams in different directions of the FeGe films,and the magnetic phase change detection of the cobalt-based coordination polymer.These works help us to understand the generation and elimination of skyrmion,magnetization mechanism of large molecular magnets..