Tunable Magnetic Properties Of Heterostructure Nano-materials

Recently, high permeability of magnetic materials at high frequency is a persistent requirement for electro devices. Thus, how to increase the permeability and the resonance frequency simultaneously is very important for improvement of high frequency theory and applications. In this PhD thesis, based on the LLG equation, which are the theoretical basis of high frequency magnetic materials, with bi-anisotropy model as the bias of the theory, the main line is to adjust the anisotropy of each systems, assist with the micromagnetic simulation method, we find the ways to improve the permeability and the resonance frequency of the soft magnetic materials. The main achievements of this paper are shown as follow:1. The high frequency properties of CoZr and CoHf thin films can be adjusted by the oblique deposition angle. With the deposition angle increasing, the anisotropy change from23-158Oe and30-152Oe, the permeability can be change from478-76and380-75, and the resonance frequency change from1.4-4.5GHz,1.8-4.3GHz.2. The static and microwave magnetic properties of (Co92Zr8/SiO2)15multilayer thin films were investigated. The in-plane uniaxial anisotropy field can be tailored from120-170Oe by adjusted the thickness of SiO2from10to1nm, and the resonance frequency can be tailored from3.47-3.87GHz correspondingly.3. Combine with the oblique technique and the adjustable interlayer interaction, the magnetic permeability and the resonance frequency of the CoHf/Ta multilayers can be adjusted in a wide range (the anisotropy change from23-118Oe, the permeability can be change from451-101, and the resonance frequency change from1.4-3.4GHz.).4. Studied the static and high frequency properties of bi-anisotropic nano-shell and nano-caps. The demagnetization field of the nano-shell and nano-caps are aimilar with the thin film while ratio of its inner and outer radius approaches1, combine with its own anisotropy become to a bi-anisotropic system. Then the static and high frequency properties were studied experimentally.5. Based on the three-dimensional micromagnetic simulations, we present a method to tailor the microwave permeabilities of magnonic metamaterials cells by a designed nano-ring structure. The results show that the permeabilities and resonant frequency are depended on the wall’s thickness of nano-rings. The underlying mechanism is ascribed to the presence of strong demagnetization fields, which are associated to the ring’s wall. In addition, the products of magnetic susceptibility and resonant frequency are larger than that predicted from Snoek’s law in polycrystalline particles. These results are direct manifestations of the bi-anisotropy model.