Synthesis And Performance Study Of Spinel Mn-Zn Ferrite Thin Films For High Frequency Applications

Stealth using radar absorbing materials enables the control or reduction of the signatures of weapon systems. National security is enhanced by new combat aircraft that use stealth materials to help control their signature, so scientists from various countries focus to develop the radar absorbing materials. The ferrite thin films have been considered as good candidates from some practical considerations such as high permeability, impedance matching, light quality, high temperature resistant and corrosion resistant. In recent years, as electronic devices have become more miniaturized, offering increasing high levels of performance, the study of electronic devices under much higher-signal frequencies has become a trend. The growth of thin layers of magnetically soft ferrites such as Mn-Zn or Ni-Zn ferrite has been studied by various groups. This trend and interest are motivated by potential applications such as magnetic thin-film read heads, cladding layers for thin film inductors and microwave acoustic devices.Owing to their large resistivities, low power losses, and high permeabilities, ferrites have become very important in high frequency soft magnetic applications. Although Mn-Zn ferrite films have such good properties including high resistivity, good quality at high frequency, and good performance of soft magnets, during their preparation there are many factors that are not easy to control. Mn-Zn ferrite is sensitive to its fabrication environment, especially at high annealing temperature. So the study of soft ferrite thin films such as Mn-Zn and Ni-Zn ferrite thin films are underway and interesting.We have prepared Mn_1-xZn_xFe₂O₄(0.1≤x≤0.9) thin films of different thickness and Zn concentration by electroless plating method in aqueous solution and rf sputter deposited method, respectively. With XRD, SEM, VSM, CEMS and an Agilent vector network analyzer (PNA 8363B). the crystallographic structure, morphology of the films. the high-frequency performance. the macroscopic magnetic properties and their correlations are characterized and discussed. The main conclusions are as follow:1. We have designed and fabricated the equipment of electroless plating. Mn_1-xZn_xFe₂O₄ (0.1≤x≤0.9) thin films of good quality with different thickness and Zn concentration were prepared on glass substrates firstly without heat treatment by electroless plating in aqueous solution at 90℃.2. The change of the coercivity of the plated Mn_1-xZn_xFe₂O₄ thin films is not consistent with that of the bulk materials. As the Zn content in the films increases, the value of H_c decreases firstly, and then increases. At x=0.5, H_c of Mn_1-xZn_xFe₂O₄ thin film shows a minimum of 3.7 kA/m and M_s shows a maximum of 419.6 kA/m. Here, M_s is much smaller and H_c is much larger than those of the bulk materials, which may be due to the following factor: the defects in the film microstructure can affect the M_s and H_c obviously: and the grain size of our samples is much smaller than that of bulk materials, which induces an increase in the number of grain boundaries, and then acts as pinning sites for domain walls , so H_c of Mn_1-xZn_xFe₂O₄ films plated is much larger than the value of the bulk materials.3. For the electroless plated Mn-Zn ferrite thin films with different Zn concentration, the Fe³⁺ ions transfer from A sites to B sites and the hyperfine magnetic field (HF) reduces with the increase of Zn content, meaning that Zn²⁺ ions have strong chemical affinity towards the A sites.4. The CEMS results indicate that the cation distribution of Mn_1-xZn_xFe₂O₄ ferrite thin films fabricated by electroless plating method and rf sputter deposited method is different from the bulk materials' and a great quantity of Fe³⁺ ions are still present on A sites, which reduces the number of unpaired spins between the A sites and B sites, so M_s of Mn_1-xZn_xFe₂O₄ thin films plated is much smaller than the value of the bulk materials.5. For the rf sputter deposited Mn-Zn ferrite thin films, H_c is much larger than those of the electroless plated thin films with same Zn content the and bulk materials.6. For the Mn_1-xZn_xFe₂O₄ ferrite thin films fabricated by electroless plating method and rf sputter deposited method, the distribution of the magnetic moments in the sample is perpendicular to the incident direction ofγ-rays. In another word, the array of magnetic moments lies in the plane thin film. For the electroless plated Mn-Zn ferrite thin films and the rf sputter deposited Mn-Zn ferrite thin films, the real partμ' of samples keep from 15 to 35 and the peak frequency f_r keep from 400 to 900 MHz corresponds to a natural resonance frequency. The peak frequency f_r is much higher than that of the bulk materials.7. For the Mn_1-xZn_xFe₂O₄ ferrite thin films fabricated by electroless plating method and rf sputter deposited method, the spectra of real and imaginary permeabilities accord with fitting the data. Damped precession of the magnetic moments corresponds to the classical Landau-Lifshitz-Gilbert formula, and the mechanism of the absorption of the high electromagnetic waves is relevant to the natural resonance theory.