Jeevan Jalli

Saturation magnetization and crystalline anisotropy calculations for MnAl permanent magnet

Theoretical saturation magnetization and magnetocrystalline anisotropy energy (MAE) of τ-phase (face-centered tetragonal) Mn50Al50 alloy were obtained by first principles calculations, and the alloy was fabricated to compare the experimental values with the theoretical predictions. The calculated magnetic moment and MAE for τ-phase Mn50Al50 were 2.37 μB/f.u. and 0.259 meV/f.u. (1.525×106 J/m3), respectively, which result in the maximum energy product (BH)max of 12.64 MG Oe and the magnetocrystalline anisotropy field of 38 kOe. The saturation magnetization for τ-phase Mn54Al46 alloy was measured to be 98.3 emu/g, which gives 4.7 MG Oe of (BH)max. The magnetization is about 70% of the theoretical value of 144 emu/g.

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

Miniaturized 0.026 ¿ Co2Z hexaferrite and Ni-Mn-Co spinel ferrite T-DMB antennas were fabricated and characterized for antenna performance. The Co2Z hexaferrites were prepared with two different processes that are water quenching and air cooling. The water quenched Co2Z hexaferrite antenna shows -6.5 dB of 3-D average gain at 190 MHz and 37 MHz of bandwidth at -10 dB. A magnetic tangent loss of water-quenched Co2Z hexaferrite was lower than that of air-cooled Co2Z hexaferrite. Compared to the hexaferrite antennas, the Ni-Mn-Co ferrite antenna shows higher frequency performance. Its gain and bandwidth were measured to be -5.83 dB at 215 MHz and 41 MHz, respectively. Omnidirectional gain pattern was observed from all fabricated ferrite antennas.

_{2}

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.

Fe

Low magnetic and dielectric loss Co2Z (Ba3Co2Fe24O41)–glass composite in the frequency range of 1–3 GHz is reported. Co2Z–glass composite was prepared by firing a mixture of 40 h shake-milled Co2Z hexaferrite powder and borosilicate glass at 950 °C for 1 h. The real part of permeability decreased slightly from 2.29 to 1.96 at 2.4 GHz as the glass content increased from 0 to 4 wt. %, but magnetic loss decreased less than 0.02. On the other hand, the real part of permittivity was 7.29 at 0 wt. % and 7.28 at 4 wt. % glass and dielectric loss was less than 0.01 at 2.4 GHz. The 3D peak gain of Co2Z–glass composite chip antenna was measured to be 3.32 dBi at 2.35 GHz. These results imply that the Co2Z–glass composite is an underpinning magnetodielectric material for gigahertz antenna applications.

_{24}

We fabricated 0.029 lambda miniaturized Co2Z hexaferrite terrestrial digital multimedia broadcasting (T-DMB) antenna. T-DMB antenna was fabricated by winding 12-turn Cu tape around the Co2Z rectangular block. Antenna was mounted on the ground substrate with connection of coaxial feeding line. Fabricated Co2Z antenna showed 196.2 MHz of center frequency, -6.55 dB of 3-D average gain and 22.13% of radiation efficiency at 195 MHz. Average gain of Co2Z antenna is found to be greater than -17.4 dB in the range of 174-216 MHz .

O

Ferrite and air-core planar inductor arrays were fabricated on 4 inch Si wafer to characterize inductor performance. Three micron thick Ni0.5Zn0.5Fe2O4 film was deposited by a low temperature electrophoresis ferrite deposition process. All ferrite inductors in the array showed 35% higher inductance (L) and 130% higher quality factor (Q) than air-core inductor. The maximum Q of ferrite inductor was found to be 53 at 2 MHz. The superimposed DC current and the rated power were measured to be about 3 A and 15 W, respectively, for a 5% drop in L. The fabricated ferrite inductor has a higher current capability than the air-core inductor. In addition, the power efficiency of the buck DC-DC converter was predicted to be 94.3% at 1.93 W.

_{41}

An array of ferrite and air-core inductors was fabricated on silicon wafer to characterize inductor performance. The 1 μm and 2.5 μm thick ferrite films for the fabrication of inductors were prepared by dc magnetron sputtering. The inductance of the ferrite inductor increased with the thickness of ferrite film from 45.5 nH for 1 μm thick ferrite to 50 nH for 2.5 μm thick ferrite. The maximum Q-factor was obtained to be 59 at 2.87 MHz from 2.5 μm thick ferrite inductor, which is higher than 49.3 at 2.26 MHz for 1 μm thick ferrite inductor and 23.2 at 1.56 MHz for air-core inductor. Superimposed dc current of 1 μm and 2.5 μm thick ferrite inductors was estimated to be 2.5 A and 2.15 A, respectively, corresponding to a 5% drop in L at 10 MHz. In addition, the power efficiency of the buck dc-dc converter based on the studied ferrite inductors was calculated to be 91.7% for 2.5 μm thick ferrite inductor and 90.1% for 1 μm thick ferrite inductor at load current of 0.647 A.

) Hexaferrite Particles

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.