High Saturation Magnetization 4πMs Research Articles

Effects of Bi2O3–CaCu3Ti4O12 composite additives on micromorphology, static magnetic properties, and FMR linewidth ΔH of NCZ ferrites

NiCuZn (NCZ) ferrites have been widely used in non-reciprocal microwave/millimeter ferrite devices, such as circulators. With the development of microwave/millimeter devices and components to high frequency, miniaturization, and lightweight applications, NCZ ferrites have needed to satisfy the essential requirements of high saturation magnetization 4πMs, low coercivity Hc, and low ferromagnetic resonance (FMR) linewidth ΔH. Herein, 0.1 wt% Bi2O3 and 0.0–3.5 wt% CaCu3Ti4O12 (CCTO) composite additives were introduced to NCZ ferrites, the influence of Bi2O3–CCTO composite additives on micromorphology, static magnetic properties, and FMR linewidth ΔH of NCZ ferrites have been demonstrated in detail. The results show that increasing the CCTO amounts in NCZ ferrites, saturation magnetization 4πMs monotonically decreases from 5484Gs to 4819Gs, and both coercive force Hc and FMR linewidth ΔH first decreases and then increases with minimums of 31A/m and 147Oe, respectively. In addition, the theory of spin-wave narrowing and the law of approach to saturation have been adopted for the separation calculation of FMR linewidth ΔH to the crystalline anisotropy linewidth ΔHa and porosity induced linewidth ΔHp. The sample with 0.1 wt% Bi2O3 and 1.5 wt% CCTO possesses high saturation magnetization 4πMs (5321Gs), remanence Br (200 mT), low coercivity Hc (31A/m), and low FMR linewidth ΔH (147Oe). The state-of-the-art NCZ ferrites with outstanding performances manifest significant applied potency for microwave/millimeter devices and components in phase array radar systems.

Epitaxial yttrium iron garnet film for fabrication of high frequency on-chip inductors

The application of epitaxial yttrium iron garnet (YIG) thin film on high frequency on-chip spiral inductors is investigated. The YIG thin film with the thickness of 3.6 μm was grown on GGG(111) substrate using the liquid phase method, which exhibits relatively high saturation magnetization 4πMs of 1615 Oe close to the bulk value of 1750 Oe and low initial coercivity Hc of 0.5 Oe that minimizes the hysteretic losses. Subsequently, the spiral inductors were directly fabricated on the YIG/GGG(111) substrate. The results show substantial improvement in the optimum operating frequency and self-resonance frequency of the on-chip spiral inductor with the YIG thin film with an increase of 50% up to ∼7.5 GHz and 14.2 GHz, respectively, implying that on-chip spiral inductors with the YIG thin film can be applied to much higher frequency RF circuits.

Effect of process temperature on structure, microstructure, residual stresses and soft magnetic properties of sputtered Fe70Co30 thin films

The effect of substrate and post-annealing temperatures on the structure, microstructure, residual stresses and soft magnetic properties of Fe70Co30 thin films was systematically investigated. Microstructural studies reveal that the films are continuous and undergo changes in shape of grain from plate like to spherical resulting in an increase in grain size with the increase in substrate temperature, whereas the post-annealed films show small pores and no significant grain growth till 500°C. Coercivity (Hc) was found decreasing with both the substrate and post-annealing temperatures; however, the best Hc value of 26Oe was obtained for the films deposited at substrate temperature of 500°C. The post-annealed films exhibited relatively higher Hc values. A good combination of high saturation magnetization 4πMs of ~23.2kG and low coercivity Hc of 26–65Oe was obtained for the films deposited at substrate temperature of 450–500°C. Residual stress analysis on films with different substrate temperatures shows the presence of tensile stress. The decrease in tensile stress is attributed to the relaxation of thermal stresses in the films.

Soft magnetic properties of (Ni80Fe20)1−x(Ni0.5Zn0.5Fe2O4)x films for high frequency applications

A series of (Ni80Fe20)1−x(Ni0.5Zn0.5Fe2O4)x films were fabricated on Si substrates by means of radio frequency magnetron sputtering and the electrical and magnetic properties were studied. Optimal films with the desired properties of low coercivity Hc ∼ 4 Oe, high saturation magnetization 4πMs ∼ 14.5 kG, and high electrical resistivity ρ ∼ 1500 μΩ cm were obtained. The permeability spectra measured shows that its natural ferromagnetic resonant frequency was about 3.4 GHz. The tested results shown that the sputtering power had an important effect on the films properties and that it can be convenient to adjust the natural ferromagnetic resonant frequency of the films.

MICROSTRUCTURES AND MAGNETIC PROPERTIES OF COBALT THIN FILMS

Cobalt thin films deposited by radio frequency sputtering were investigated. Microstructures of the Co films were analyzed by XRD and TEM. The results show that films microstructure varies with the variation of the sputter gas pressure P Ar . Magnetic properties measured by VSM show that all the films possess relatively high saturation magnetization 4πMs, and strong in-plane uniaxial magnetic anisotropy field Hk. Co films deposited below 0.3 Pa show soft magnetic properties and its microwave permeability was measured by vector network analyzer in the 0.1–5 GHz range.

Fe–Co–B/[Ni–Fe/Si] soft magnetic underlayer with high anisotropy field along cross-track direction on disk substrate

The origin of high anisotropy field Hk and low coercivity Hc of Fe–Co–B/Ni–Fe double-layered films with high saturation magnetization 4πMs was investigated. In-plane and out-of-plane X-ray diffractometry studies clarified that the lattice spacing of crystallites along the easy axis direction was expanded compared to that along the hard axis direction. It was confirmed that such an anisotropic residual stress caused the magnetic anisotropy energy of the double-layered film through magnetoelastic effect. Investigation of Ar gas pressure dependence of Hk suggested that the origin of the residual stress was due to the oblique incidence of sputtered particles. In order to align the orientation of magnetic anisotropy field along the cross-track direction, a Fe–Co–B/Ni–Fe double-layered soft magnetic underlayer was deposited on a rotating disk. The Fe–Co–B/Ni–Fe double-layered films on the rotating disk exhibited Hk values above 200Oe along the radial direction of the disk in the whole area of the disk.

High moment soft magnetic FeTiN thin films for recording head materials

Soft magnetic properties and thermal stability of Fe–Ti–N alloys films have been investigated. Thin films with composition in the range of 8–10 at. % Ti, 10.5–14 at. % N, and balance Fe were prepared by reactive sputtering method. The films exhibit good soft magnetic properties in the as-deposited condition without any post heat treatment, e.g., low coercivity Hc∼1.5 Oe, high permeability μ∼3200 at 1 MHz and very high saturation magnetization 4πMs∼24 kG. The thermal stability of these films was also found to be good, e.g., Hc was less than 2 Oe, and 4πMs was higher than 23 kG for the films annealed up to 500 °C. The high electrical resistivity ρ∼100 μ Ω cm of the films can minimize the eddy current loss in the high frequency applications. The combination of high 4πMs and relatively high anisotropy field Ha∼10 Oe in the film is conductive to the suppression of the undesirable ferromagnetic resonance interfere up to the GHz frequency range.

Deposition of Amorphous CoZrNb Films Using CMF Magnetron Sputtering Technique

Amorphous CoZrNb films with high saturation magnetization 4πMs of about 14 kG and low coercivity Hc of about 0.3 Oe have been successfully prepared by the CMF magnetron sputtering technique with a CoZrNb alloy target. Hc and 4πMs along the easy axis were changed by background pressure, film thickness and Ar pressure Pr. The applied voltage of discharge operation is as low as 270 V at Pr of 0.3 Pa. The maximum deposition rate is as large as 0.13 µm/min for a power density of 4.42 W/cm2. The target utilization efficiencies are improved in spite of using a magnetic target because a leakage magnetic field increases more to a greater extent by attaching an outer pole piece. These are about 95% and 60% in surface area and in volume, respectively. The changes in a film thickness of 1 µm deposited on the substrate were 0.05 µm at Pr of 0.2 Pa, and 0.06 µm at a distance of 50 mm between substrate and target, respectively.