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We present here, the results of a thorough study of the longitudinal permeability ratio (LPR) and transverse permeability ratio (TPR) in sputtered Co 19.35 Fe 53.28 Hf 7.92 O 19.35 films with varying thicknesses (t = 1, 1.5, 1.8 and 2.4 μm) in the frequency range of 100 - 1000 MHz. It is found that for all samples investigated, the LPR/TPR first increases with increasing frequency, reaches a maximum at 710 MHz, and then decreases at higher frequencies. This is related to the ferromagnetic resonance. The LPR and TPR profiles measured along the easy axis of the film show a single-peak feature, whereas those measured along the hard axis of the film show a double-peak one. This indicates an existence of magnetic anisotropy and its dispersion in the films. It reveals that the study of LPR and TPR spectra provides an alternative way for the evaluation of the high-frequency magnetic softness of film-type materials.

This paper reports on the excellent high-frequency magnetic performance of Co-Fe-Hf-O thin films, which were deposited on Si(100) substrates by the oxygen reactive rf-sputtering method. It was shown that the films possessed not only high electrical resistivity but also large saturation magnetization and hard-axis anisotropy field. Among the compositions investigated, Co 19.35 Fe 53.28 Hf 7.92 O 19.35 exhibited the ultrasoft magnetic properties of high saturation magnetization, 4πM s ∼19.86 kG, and low coercivity, H c ∼1.5 Oe. The magnetic permeability remained almost constant up to 3 GHz and reached a maximum at the ferromagnetic resonant frequency of 4.024 GHz. These properties of this film together with a high electrical resistivity of 3569 μΩcm make it ideal for producing micromagnetic devices for high-frequency applications.

Fe-Al-O thin films exhibit good magnetic properties. However, their application in RF devices is mainly restricted by the low ferromagnetic resonance frequency. For practical applications it would be useful to try to shift this frequency to higher regions by exploiting the extra anisotropy induced by patterning the film. In this work, we discuss a model describing the permeability behavior as a function of frequency in patterned film samples and apply this model to explain experimental results for patterned Fe 87.3 Al 4.2 O 8.5 thin films.

The exchange bias (HE) coupling in MnCr/Co bilayers has been analysed. The exchange bias and coercivity (Hc) of the samples were investigated as a function of temperature. They reached the largest value for an annealing temperature of 300 °C at a measuring temperature of 123 K. Moreover, HE and Hc also exhibited a dependence on the thickness of ferromagnetic and antiferromagnetic layers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of microstructures on the electrical and magnetic properties of Co-Fe-Al-O thin films was studied using X-ray diffraction (XRD) analysis and conventional transmission electron microscopy (TEM). The results showed that excellent soft magnetic properties were associated with granular nanoscale grains of α-CoFe and α-Co(Fe) phases. The introduction of aluminium and oxygen to CoFe films led to a refinement of the granular microstructure. When the partial pressure of oxygen was less than 4%, oxide particles CoFe 2 O 4 , CoAl 2 O 4 or FeAl 2 O 4 were embedded in α-CoFe, α-Co(Fe) grains. A higher partial pressure of oxygen changed the crystalline oxide to amorphous oxide, resulting in the formation of smaller grains of α-CoFe and α-Co(Fe) phases. The partial pressure of oxygen caused drastic changes in the coercivity (H c ), anisotropy field (H k ), and electrical resistivity (p), the reason for which was discussed based on the microstructural observations and X-ray diffraction results. Co-Fe-Al-O thin films exhibit excellent high frequency characteristics: an effective permeability larger than 1000 and stability above 1 GHz.