Preparation Of Ni-Zn Ferrite Nano-composites,Magnetic And Microwave Absorption Properties

The spinel structure Ni-Zn of is an important functional magnetic material, because of its high resistivity, low temperature coefficient, high Curie temperature and excellent high-frequency performance; it plays a great role in the application field such as high-frequency inductor core, transformers, magnetic recording materials and microwave absorbing materials etc. In recent years, nickel-zinc ferrite nano-structured materials received wide attention, due to it high microwave permeability, high resonance frequency, and excellent microwave absorption properties in300MHz to3GHz frequency range, which indicated as a potential good microwave absorbing materials in microwave communication band. This paper adopted the following two ways to improve its high frequency magnetic properties and microwave absorption performance:(1)Synthesized nickel-zinc ferrite nano-crystalline materials, and the high-frequency magnetic-behavior of Ni-Zn ferrite nano-particles;(2) Synthesized SrFe12O19/Ni0.6Zn0.4Fe2O4nano-composites, and comparing the materials’ high-frequency magnetic behavior and microwave absorbing performance of nano-composites with those of single-component material. The main content of this paper is summarized as follows:1. Using nitrate, sodium hydroxide (analytical grade) as the reagent, the nano-crystalline Ni0.6Zn0.4Fe2O4powders were synthesized at low temperature by the hydrothermal method, the crystallite size of the sample is about20nm with uniform grain size and good dispersion. The effect of annealing temperature on the microstructure and magnetic properties of the material was studied. At the annealing temperature of1000℃, the saturation magnetization and coercivity of the samples reaches58.75emu/g and174.4Oe respectively.2. The as-prepared Ni-Zn ferrite nano-crystalline powders are dispersed into wax based on mass ratio (3:2) and compacted into rings for the permeability and permittivity measurement. The size of the ring is7mm in outer diameter,3mm in inner diameter and3mm in thickness. The complex permeability and complex permittivity of Ni-Zn ferrite/wax nano-composite in the frequency range of300MHz～2GHz are measured with an s-parameter Network Analyzer. The results show that the real part(μr)of permeability of nickel-zinc ferrite nano-material decreases monotonically with the frequency increased, the imaginary part (μr) of penneability firstly increases and then slowly reduce, the frequency dispersion of permeability behaves like relaxation-type domain-wall resonance. The real part(μr)of permeability for non-annealing sample and1000℃annealing sample both changes between1.3and3.1, and the imaginary part (μr)of permeability both changes between0and0.74. The real part(εr) of dielectric permittivity both changes between3.32and3.87, the dielectric loss changes between0and0.068, at the2GHz, the reflection loss of sample coating with the thickness of8mm reaches4.5dB. The Ni-Zn ferrite nano-crystalline materials present high microwave permeability, high magnetic loss, low dielectric constant and low dielectric loss in300MHz-2GHz band, which have an important application in the field of microwave absorption, magnetic therapy and microwave heating therapy.3. The SrFe12O19/Ni0.6Zn0.4Fe2O4composites were prepared using in-situ hydrothermal method. The microstructure, magnetic properties, and microwave absorption properties of SrFe12O19/Ni0.6Zn0.4Fe2O4composites were investigated, when the content of Ni0.6Zn0.4Fe2O4increase, the saturation magnetization of the composite slightly decreases, while the coercivity decreases rapidly. The saturation magnetization and the coercivity force of pure SrFe12O19material reaches62.52emu/g and1309.1Oe, respectively, while, The saturation magnetization and the coercivity force of SrFe12O19/wt40%Ni0.6Zn0.4Fe2O4composite reaches57.13emu/g and447.9Oe. In addition, the microwave absorption properties of composites decreased with the content of Ni0.6Zn0.4Fe2O4increase in the8GHz-15GHz frequency range, it can be ascribed to the decrease of magnetic anisotropy and saturation magnetization of the composites with the content of Ni0.6Zn0.4Fe2O4increase.