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Jalli, Jeevan,Hong, Yang-Ki,Bae, Seok,Lee, Jae-Jin,Abo, Gavin S.,Lyle, Andrew,Gee, Sung-Hoon,Lee, Hwachol,Mewes, Tim,Sur, Jeong-Chul,Lee, Sung-Ik American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>Liquid phase epitaxy technique was used to grow 144 mu m thick barium ferrite (BaFe12O19; BaM) single crystalline films on (111) Gd3Ga5O12 substrate. The growth rate of 72 mu m/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 (4 pi M-s) and the anisotropy field (H-k) were found to be 4.2 kG and 16.0 kOe, respectively. The ferrimagnetic resonance linewidth (Delta H) at 35 GHz was measured to be 0.1 kOe. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3062824]</P>
Gavin S. Abo,Yang-Ki Hong,Jeevan Jalli,Jaejin Lee,Jihoon Park,Seok Bae,Seong-Gon Kim,Byoung-Chul Choi,Terumitsu Tanaka 한국자기학회 2012 Journal of Magnetics Vol.17 No.1
The coercivity of a single 27 nm-spherical barium ferrite (S-BaFe) particle was simulated using three models: 1) Gibbs free energy (GFE), 2) Landau-Lifshitz-Gilbert (LLG), and 3) Stoner-Wohlfarth (S-W). Spherically and hexagonally shaped particles were used in the GFE and LLG simulations to investigate coercivity with the different shape anisotropies. The effect of shape was not included in the S-W model. It was found that the models using a spherical shape resulted in a coercivity higher than the models using the hexagonal shape with both shapes having the same diameter. The coercivity estimated with the S-W model was approximately the same as that for the spherical-shape models, which indicates that spherical shape has no significant effect on the particle’s coercivity at nanoscale.
Optimized Design of Low Voltage High Current Ferrite Planar Inductor for 10 ㎒ On-chip Power Module
Seok Bae,Yang-Ki Hong,Jae-jin Lee,Gavin Abo,Jeevan Jalli,Andrew Lyle,Hongmei Han,Gregory W. Donohoe 한국자기학회 2008 Journal of Magnetics Vol.13 No.2
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 ㎒, and resonance frequency (?r) 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 ?r of 316.3 ㎒ were obtained with coil space of 127 ㎛, Cu thickness of 67.8 ㎛, ferrite thickness of 130.3 ㎛, 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.
Spin-polarized Current Switching of Co/Cu/Py Pac-man type II Spin-valve
Andrew Lyle,Yang-Ki Hong,Byoung-Chul Choi,Gavin Abo,Seok Bae,Jeevan Jalli,Jae-jin Lee,Mun-Hyoun Park,Ryan Syslo 한국자기학회 2010 Journal of Magnetics Vol.15 No.3
We investigated spin-polarized current switching of Pac-man type Ⅱ (PM-Ⅱ) nanoelements in Pac-man shaped nanoscale spin-valves (Co/Cu/Py) using micromagnetic simulations. The effects of slot angle and antiferromag-netic (AFM) layer were simulated to obtain optimum switching in less than 2 ns. At a critical slot angle of 105˚, the lowest current density for anti-parallel to parallel (AP-P) switching was observed due to no vortex or antivortex formation during the magnetic reversal process. All other slot angles for AP-P formed a vortex or antivortex during the magnetization reversal process. Additionally, a vortex or anti-vortex formed for all slot angles for parallel to anti-parallel (P-AP) switching. The addition of an AFM layer caused the current density to decrease significantly for AP-P and P-AP at slot angles less than 90˚. However, at slot angles greater than 90˚, the current density tended to decrease by less amounts or actually increased slightly as shape anisotropy became more dominant. This allowed ultra-fast switching with 5.05 and 5.65 x 10? A/㎠ current densities for AP-P and P-AP, respectively, at a slot angle of 105˚.
Seok Bae,Yang-Ki Hong,Jaejin Lee,Jihoon Park,Jeevan Jalli,Gavin S. Abo,Hyuck M. Kwon,Chandana K. K. Jayasooriya 한국자기학회 2013 Journal of Magnetics Vol.18 No.1
A pulsed ferrite magnetic field generator (FMFG) was designed for the use in the 1000 m long through-theearth (TTE) communication system for mining disaster situations. To miniaturize the TTE system, a ferrite core having 10,000 of permeability was used for the FMFG. Attenuation of the magnetic field intensity from the FMFG (200-turn and 0.18 m diameter) was calculated to be 89.95 ㏈ at 1000 m depth soil having 0.1 S/m of conductivity. This attenuation was lower than 151.13 dB attenuation of 1 ㎑ electromagnetic wave at the same conditions. Therefore, the magnetic-field was found to be desirable as a signal carrier source for TTE communications as compared to the electromagnetic wave. The designed FMFG generates the magnetic field intensity of 1 × 10?¹? Tesla at 1000 m depth. This magnetic field is detectable by compact magnetic sensors such as flux gate or magnetic tunneling junction sensor. Therefore, the miniature FMFG TTE communication system can replace the conventional electromagnetic wave carrier type TTE system and allow reliable signal transmission between rescuer and trapped miners.