A. Lyle

New Synthetic Route of Z-Type (Ba

Z-type barium hexaferrite particles were synthesized by a one-step mixing-calcination process (MCP) and its magnetic properties were characterized and compared to the sol-gel (SGP) and the conventional ceramic (CCP) processed Z-type Ba hexaferrite with two-step calcination. We have used 71.2% pure M-type (BaFe12O19) and 83.8% pure Y-type (Ba2Co2Fe12O22) precursors to synthesize Z-type by the MCP. As a result, 77.8% pure Co2Z hexaferrite particles were obtained. The purities of Co2Z hexaferrite particles processed by SGP and CCP were 75.1% and 70.7%, respectively. It was found that purity of Z-phase was controllable by purity of M- and Y-type precursor particles in the MCP. Loss tan delta of sintered MCP Co2Z decreased from 0.17 at 50 MHz to 0.068 at 300 MHz, while loss tan delta of sintered SGP and CCP Co2Z were 0.12 and 0.09 at 300 MHz. It is found that this loss tan delta is controllable by the purity of Z-phase and sintering process. These results imply that our new process is potentially applicable to synthesis of any other hexaferrites and also cost-effective.

_{3}

Magnetic properties of sol-gel and conventional ceramic processed Ba3Co2Fe2O41 hexaferrite were investigated and compared for terrestrial digital multimedia broadcasting (T-DMB) antenna application. All of the synthesized powder and sintered body showed almost single Z-phase. The loss tan δ of sol-gel processed and sintered Co2Z hexaferrite was 0.010 at 200 MHz, while conventional ceramic processed and sintered Co2Z showed 0.068. The ωd (resonance frequency of domain wall) and ωs (resonance frequency of spin components) of sol-gel and ceramic processed hexaferrites were estimated to be 10 and 1160 MHz and 17 and 1025 MHz, respectively. The frequency difference between ωd and ωs (1150 MHz) for the sol-gel processed hexaferrite is wider than that (1008 MHz) for the ceramic processed hexaferrite. The permeabilities of sol-gel and ceramic processed hexaferrites were 6.91 and 9.23 at 200 MHz, respectively. Both permeabilities are higher than 6.88 and 7.64 of corresponding permittivities at the same frequency, ...

Co

We fabricated 3 times 3 array of 1 mum thick Ni-Zn-Cu ferrite and air-core planar inductors (5 times 5 mm2 in size; 2.5, 3.5, and 4.5 turns of Cu coil) on 4 inch bare Si wafer and 300 nm thick SiO2/Si wafer, respectively. The ferrite inductor showed higher Q than that of air-core inductor in the range of 7 to 100 MHz. The Q (= 19.5) of 4.5 turn ferrite inductor is 3.3 times higher than that (= 5.9) of 4.5 turn air-core inductor at 10 MHz, and inductance (L) increased by 10%. The Q-factors were found to be about 50 at 2.3 MHz and 20 at 10 MHz, respectively, for the ferrite inductor.

_{2}

Performance of inverted F meander antenna with a lossy ferrite film was investigated and compared to air-core antenna with the same design. We have fabricated ferrite film antenna using 3μm thick plated Ni0.21Zn0.45Fe2.34O4. Loss tanδμ of the plated ferrite was about 1.5 around 500MHz. It was found that bandwidth significantly increased by the use of lossy ferrite, while radiation efficiency (RE) decreased. However, the RE increases as the thickness of lossy ferrite film decreases below 10μm. The fractional bandwidth of ferrite film antenna was found to be 13.8%, which shows a 431% as compared to an air-core antenna. The center frequency (fc) for ferrite film antenna decreased from 584to534MHz of the air-core antenna. This implies 7.5% decrease in the fc, while the gain of the ferrite was not much lower than the air-core antenna. Lossy ferrite thin film has been found to be effective in broadening of bandwidth, while retaining an acceptable gain.

Fe

A combination of energetic shake-milling and a subsequent double sintering process was employed to synthesize Co_0.8Zn_1.2Z (Ba₃Co_0.8Zn_1.2Fe₂₄O ₄₁) hexaferrite nanoparticles with a high-saturation magnetization and a low coercivity. A homogeneous mixture of BaCO₃, CoO, ZnO, 40-nm sized alpha-Fe₂O₃, and heat-treating in an oxygen environment were important factors for synthesizing single-phase Co₂Z-type ferrite nanoparticles. In addition to an X-ray diffraction pattern, Mossbauer spectra confirmed that only Fe³⁺ cations are present in the synthesized Co_0.8Zn_1.2Z particles, implying single phase of the particles. Low-temperature sintering processing, 900degC, was then successfully applied to the single-phase Co_0.8Zn_1.2Z particles. The coercivities of the Co _0.8Zn_1.2Z powder and the low-temperature sintered disk were 9 and 20 Oe, respectively, while maintaining the saturation magnetization of 50 emu/g

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In this paper, design parameters of high Q (> 50), high current inductor for on-chip power module were optimized by 4 Xs 3 Ys DOE (Design of Experiment). Coil spacing, coil thickness, ferrite thickness, and permeability were assigned to Xs, and inductance (L) and Q factor at 10 MHz, and resonance frequency ( fr) were determined Ys. Effects of each X on the Ys were demonstrated and explained using known inductor theory. Multiple response optimizations were accomplished by three derived regression equations on the Ys. As a result, L of 125 nH, Q factor of 197.5, and fr of 316.3 MHz were obtained with coil space of 127 μm, Cu thickness of 67.8 μm, ferrite thickness of 130.3 μm, and permeability 156.5. Loss tan δ = 0 was assumed for the estimation. Accordingly, Q factor of about 60 is expected at tan δ = 0.02.

O

Liquid phase epitaxy technique was used to grow 144 μm thick barium ferrite (BaFe12O19; BaM) single crystalline films on (111) Gd3Ga5O12 substrate. The growth rate of 72 μm/h was achieved with a flux system of Fe2O3–BaCO3–Na2CO3. The grown BaM films show single crystalline (000l) orientation that was confirmed by x-ray diffraction and magnetic torque curves. The saturation magnetization (4πMs) and the anisotropy field (Hk) were found to be 4.2 kG and 16.0 kOe, respectively. The ferrimagnetic resonance linewidth (ΔH) at 35 GHz was measured to be 0.1 kOe.

_{41}

Samarium (Sm) doped M-type strontium ferrite single crystals have been successfully grown from melts using a flux system of SrCO3 and Na2CO3. The crystals exhibited the typical hexagonal ferrite growth habit with a plate-like geometry, and the largest crystals obtained are of 10 mm in length and 3-4 mm in thickness, respectively. It was observed that the saturation magnetization and anisotropy field are greatly affected by the doping concentration of Sm. A saturation magnetization (sigmas) of 69.8 emu/g and an anisotropy field (H k) of 25 kOe was achieved. Room temperature FMR measurements show 85 Oe of linewidth (DeltaH) at 53 GHz.

) Hexaferrite Particles

Interactions between neighboring cells become increasingly important due to the miniaturization of magnetoelectronic devices. This paper studies the effect of magnetic interaction on the switching behaviors in two different configurations of paired Pac-man shape Permalloy elements: back-to-back and face-to-face configurations. From as-patterned state MFM images, it is observed that the face-to-face configuration is prone to form either two single domains with an antiferromagnetic configuration, one single domain with one vortex or a double vortex configuration. MOKE hysteresis loops show that the coercivity for the face-to-face configuration is smaller than the back-to-back configuration. These experimental results indicate that the back-to-back configuration has weaker interaction between the two Pac-man elements than the face-to-face configuration. We further varied the aspect ratio of Pac-man elements in the pair arrays to tune the magnetic interaction. It was found that the coercivity of pair array increased with the higher cell aspect ratio. Micromagnetic simulation was also performed to simulate the switching process for the two different configurations. Overall, the back-to-back configuration is recommended for applications that demands less inter-cell interactions.

Low loss Z-type barium ferrite (Co2Z) for terrestrial digital multimedia broadcasting antenna application

We investigated spin-polarized current switching of elongated Pac-man (EPM) elements in a Pac-man shaped spin valve (Co/Cu/Py). The aspect ratio, pulse duration, and effect of antiferromagnetic (AFM) layer were simulated to obtain coherent switching. Pulse duration was varied on the picosecond (ps) scale and showed that ultra-fast switching could be achieved. A critical aspect ratio of 4.2 was found, where a minimum current density was observed. For antiparallel to parallel (AP-P) switching, a vortex formed during the switching process for aspect ratios less than 7. Aspect ratios of 7 or higher did not form a vortex and showed similar current densities to parallel to antiparallel (P-AP) switching as a result. It was found that the AFM layer prevented the formation of a vortex at the critical aspect ratio of 4.2 and effectively changed the switching mechanism. This allowed coherent switching with current densities for AP-P and P-AP to be only 7% from each other at the aspect ratio of 4.2.