Structure and Magnetic Properties of the Ni-Zn Ferrite Films for High-frequency Applications
|Condensed Matter Physics
|radio frequency magnetron sputtering the ferrite films soft magnetic property resonance frequency bianisotropy model
Recently, due to the ongoing trend for miniaturization and steadily increasing operating frequencies into the gigahertz range of electronic devices, Ni-Zn ferrite films with high resonance frequency, large resistivity, excellent wear resistance, and stable chemical property have been in attention extensively. In this thesis, the Ni-Zn ferrite powers have been prepared by chemical co-precipitation method firstly. And then they were pressed and sintered into the targets, which were used in the sputtering procession. The Ni-Zn ferrite films were deposited onto Si(111) substrates by radio frequency (RF) magnetron sputtering. The structural, morphological and magnetic properties were investigated systematically by the X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer, and vector network analyzer. The main results were as follows:1. We have realized in situ fabricated well-defined Ni-Zn ferrite films by sputtering without any heating treatments, and they had better soft magnetic property. The saturation magnetization of the Ni0.45Zn0.55Fe2O4 film with 300 nm was about 237.2 emu/cm3, which was much larger than that of other films in situ deposited without heated in the reports.2. The resonance frequency (fr) of the Ni-Zn ferrite films deposited by magnetron sputtering has been in the GHz range, which was much higher than the corresponding ferrite bulks and exceeding Snoek’s limit for Ni-Zn ferrite bulk. And the reason why the ferrite films have high fr has been explained by making use of the bianisotropy model.3. The ZnFe2O4 films deposited by magnetron sputtering without any heating treatments were single-phase with spinel structure and had strong ferromagnetic property at room temperature. The effect of thermal annealing on structural and magnetic properties has been investigated for ZnFe2O4 films. It was found that the magnetic property of ZnFe2O4 films annealed at relatively low temperature of 200℃was the most excellent. It had large saturation magnetization, high resonance frequency, large permeability and better noise suppression property. The resonance mechanism of the ZnFe2O4 films has been investigated, and it was considered that the resonance model was the nature resonance.4. [FeMn/Ni-Zn ferrite] layered composite films have been deposited by inserting the antiferromagnetic material of Fe50Mn50. The influence of FeMn layer on the microstructure and magnetic property of Ni-Zn ferrite film was investigated. It was found that the remarkable reduction of grain size and uniformity of grain morphology of the Ni-Zn ferrite films were obtained by introducing a FeMn layer. The magnetic softness of the ferrite film was optimized, and the coercivity decreased to 38 Oe. The high-frequency magnetic property has been improved, and the resonance frequency achieved to 1.8 GHz.5. [CoNb/Ni-Zn ferrite] layered composite films have been deposited by inserting the soft magnetic metallic material of Co9oNb10. The influence of the thickness of the Ni-Zn ferrite layer on the microstructure and magnetic property of the composite films was investigated. It was found that the saturation magnetization of the layered composite films decreased with the increasing of the thickness of the ferrite layer. However, the resonance frequency and the resonance line width increased steadily. Begin from the composite film with the ferrite layer of 10 nm, the imaginary part of permeability has shown two resonance peaks. It was because that the exchange coupling action between the metal layer and the ferrite layer in the composite films has been weakened with the increasing of thickness of the ferrite layer.