Magnetic printing simulations of conventional and AFC media were performed by solving the Poisson equation for a two-dimensional model of patterned master films and a slave disk system. When the applied field for the printing is weak, the recorded magnetizations in the medium of the slave disk cannot be switched in the central region between patterned films, and the output waveforms for the recorded magnetizations are severely distorted, producing subpulses for both media. On the other hand, when the applied field is strong, though the recorded magnetizations can be switched completely, the output waveforms are also distorted, with the peaks shifted to the center of the soft magnetic patterned films. As a result, there exist optimum applied fields dependent on the patterned film thickness and the patterned interval of themaster disk. Furthermore, it is shown that the recorded magnetizations in the AFC medium just after printing are parallel between two recording layers and become antiparallel about 100 sec. after printing.
“ Proximity effects” could be the superior mechanism responsible for lowering the quality factor (Q) of ferromagnetic spiral inductors, apart from ferromagnetic resonance considerations. In this paper, a model extraction from previous measurements is described. In particular, the extracted series resistance Rs is discussed with regards to skin depth and current crowding contributions in the metal traces. Comparing air-core and ferromagnetic spirals, it is shown that“ proximity effects” are enhanced with magnetic materials leading to a much stiffer increase in Rs with frequency (f2 instead of √ f). This points out Q being naturally always lowered at the same frequency with ferromagnetic spirals, even if an adequate high FMR is realized. Thus, it is necessary to reconsider the design of spirals when using magnetic materials and some solutions are suggested at the end of this paper.
The GMI effect has been studied in 3 different families of amorphous wires: conventional amorphous wires (125 μ m; m in diameter), cold drawn wires (50 and 20 μ m in diameter) and thin glass coated amorphous microwires (with metallic nucleus diameter of about 15 μ m) has been investigated in the frequency range 1 500 MHz. A remarkable difference in magnetic field dependence of the GMI effect can be attributed to the different magnetoelastic anisotropy of these three families of the wires.
Impedance measurements as a function of the applied magnetic field are performed at high frequency using an experimental set-up specially adapted for planar samples, which is based on a microstrip transmission line. Microwave measurement techniques and a consistent data reduction procedure allow obtaining very detailed and accurate impedance measurements. The results for two different samples, an amorphous ribbon and a trilayer thin film, reveal the importance of the ferromagnetic resonance contribution at high frequency. Besides, fine details of the magneto-impedance behavior at low field confirm that it is mainly governed by magnetization processes. At high frequency, when the ferromagnetic resonance contribution at low field weakens, an impedance peak re-appears, that seems to be related with the usual peak that exists at low frequency.
Present study reports on magnetostatic interactions in highly-ordered arrays of Ni nanowires embedded in nanoporous alumina membranes. We use two techniques supplying complementary information: ferromagnetic resonance, FMR, studies from which we derive information of the whole array of nanowires, and magnetic force microscopy, MFM, that informs us about the magnetic state of individual nanowires. From FMR study of the angular dependence of resonance field and itsline-width it is concluded that the magnetostatic interaction plays an important role to decrease the effective anisotropy field of individual nanowires. This is confirmed by analysis of MFM images at remanence and its comparison with vibrating sample magnetometer measurements.
Previously we revealed that spin-sprayed ferrite films are usable for GHz-range noise suppressors. For actual use, the films must retain excellent characteristics after the reflow soldering process. In this study, we investigated how changing the compositions of films influences their electric resistivity and the noise suppression effects obtained after annealing at 260° C. We plated 3-μm-thick ferrite films #1 (Ni0.2Zn0.1Fe2.7O4) and #2 (Ni0.4Zn0.3Fe2.3O4) onto polyimide sheets. The resistivity of film #1 decreased markedly, from 4 × 102 Ω cm to 1 × 100 Ω cm as a result of the annealing. On the other hand, film #2 exhibited a smaller decrease, from 6 × 104Ω cmto2 × 104 Ω cm. The reflection parameter S11 and transmission loss Δ Ploss measured on a microstrip line for film #1, especially below 1 GHz, were increased by the annealing. This is unfavourable for use of film #1 in lowpass filters that are required to absorb noises only in the GHz range. On the other hand, S11and Δ Ploss for film #2 were not significantly affected by the annealing. This film exhibited Δ Ploss of 40 ‰ at 10GHz.Moreover, the value of S11for the film below 10 GHz was sufficiently weak, less than -12dB.Thus, we succeeded in fabricating aGHz-rangenoise suppressor, with excellent heat resistance.
Significant size reduction for RF spiral inductors is shown possible with using high magnetization (4 π Ms) ferromagnetic material. High 4 π Ms (-19kG) is suitable for realizing high ferromagnetic resonance frequencies FMR (-6GHz) and significant L-enhancements thanks to a high permeability. However, increasing the natural resistivity of FeHfN (-102 μ Ohm.cm) would be also advantageous for a better confinement of the magnetic flux and reducing the series-capacitance with the inductor. Indeed, with a very high resistivity (typically= 103 μ Ohm.cm), the magnetic materials can be almost in contact to the metal traces, therefore reducing the gap between the spiral and the magnetic planes. In a first part, we detail the optimization of FeHfN single layer films and the realization of ferromagnetic spiral inductors integrating this film as a laminated material. The results point out 30% to 130% increase in L over the air-core value which leads to a surface reduction of 25% to 50%. In a second part, we investigate the possibility of coincorporation of oxygen and nitrogen in FeHf films in order to raise the resistivity and to retain a high magnetization. It is shown that nitrogenation and oxidation processes act separately with opposed effects on the microstructures of the films (grain size, lattice parameter.) but combine advantageously. However, the expected compromise with 4 π Ms above-10kg and a resistivity of-103μΩ. cm has not been found yet. Finally, it is concluded that the dual N2-O2-reactive process with FeHf material is promising but requires further investigations.
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