Theoretical Study On Complex Susceptibility Of Nano-particle Films

For decades, the study of the nano film material has received extensive attention due to its unique capability in the optical, magnetical and electrical fields. The study of complex susceptibility has a guiding significance in preparation and improving the absorbing of absorbing materials. In this paper, the complex susceptibility of a disordered nano-particle film is analyzed theoretically, according to the Landau-Lifshitz equation.The paper is divided into three parts. In the introduction, an overview of nano-absorbing materials is introduced and the international achievements are reviewed. In the second chapter, the model describing nano-particle film is introduced; the expressions of the anisotropy, dipole-dipole, and exchange equivalent fields are given; the equations of complex susceptibility in an ac magnetic field with high frequency and weak amplitude are deducted. In the third chapter, for different kind of interaction, the complex susceptibility of the film in which the particles with random orientation and directional orientation is studied. The main conclusions are as follows:1. When the easy magnetization axes of the nano-particles are randomly orientated, the complex susceptibility of the system with the dipole-dipole interaction (D) or with the exchange interaction (J) is calculated, and the relaxation and the resonance magnetic spectrums are obtained, we analyzed the dependence of dipole-dipole interaction and exchange interaction on the real part, the imaginary part, the maximum of the imaginary part, the resonance frequency, and the resonance line width of complex susceptibility. For the resonance magnetic spectra, it's found that the curve of the imaginary part of the complex susceptibilty split in a system with strong dipole-dipole or exchange interaction, which may be caused by non-uniform resonance phenomenon.2. Also in the randomly oriented nano-particle film, the complex susceptibility of the system with both the dipole-dipole and the exchange interaction is calculated. The D-J graph is drawn to expatiate on the relations of the microwave properties of the film with D and J. It is easily found that the microwave properties of the film show complex relations with the dipole-dipole and exchange interaction.3. When the easy magnetization axes of the nano-particles in the film are directionally orientated, the complex susceptibility of the system with different interactions is calculated. For the relaxation and the resonance magnetic spectra, we analyzed the dependence of the real part, the imaginary part, the maximum of the imaginary part, the resonance frequency, and the resonance line width of complex susceptibility on anisotropy angular dispersion.