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Spontaneous Domain Wall Motion at Zero External Magnetic Field in Ferromagnetic Nanowire
Djuhana, D.,Hong-Guang Piao,Je-Ho Shim,Sang-Hyuk Lee,Su-Hyeong Jun,Seong-Cho Yu,Suhk Kun Oh,Dong-Hyun Kim IEEE 2010 IEEE transactions on magnetics Vol.46 No.2
<P>We have explored a spontaneous domain wall motion in ferromagnetic nanowire at zero external magnetic field by means of micromagnetic simulation. Very interestingly, even with no external magnetic field, a spontaneous domain wall motion is observed with a speed about few tens of m/s, which is significant and not negligible in analysis of the domain wall dynamics on nanowires. The spontaneous zero-field wall motion is explained based on the minimization condition of the magnetostatic energy, preferring to have a wire magnetically saturated. Average speed of the spontaneous wall motion is found to increase as the wire thickness increases.</P>
Dede Djuhana,Candra Kurniawan,김동현 한국물리학회 2018 Current Applied Physics Vol.18 No.2
The complete understanding of domain wall (DW) dynamics is important in the design of future spintronic devices. The characteristics of faster time-scale and lower current amplitude to move DW along nanowire are crucial in fabrication upgrade. In this study, we have investigated depinning behavior of magnetic domain wall triggered by nanosecond current pulse in notched Permalloy nanowires by means of micromagnetic simulation. We introduced double-triangular notch as the constrictions in the nanowire. The non-adiabaticity of the spin-transfer-torque is considered in simulation by varying the non-adiabatic constant (β) value. We observed that the depinning current density (Jd) was not significantly affected by β for notch size (s) < 50 nm. Interestingly, we found that the depinning time (td) for β ≥ 0.04 was slightly constant for all the cases with s > 70 nm, where the DW structure was kept to be a transverse structure during the depinning process. The broadly applicable depinning behavior is considered to contribute to the development of high-speed memory storage devices based on magnetic domain wall.
Dede Djuhana,Bambang Soegijono,Hong-Guang Piao,Suhk Kun Oh,Seong Cho Yu,김동현 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have investigated the domain wall (DW) depinning behavior around the symmetric notches inferromagnetic nanowires by means of a micromagnetic simulation. We observed that the depinningfield decreases as the size of the notch increases. The change in the ratio of the height to the lengthof the bottom of the triangular notch is also considered, and a relatively insensitive variation of thedepinning field is observed with for ratios greater than 2. When the depinning field strength is varied,the DW internal structure is found to change during the depinning process. At a lower depinningfield (< 4 mT), the DW keeps its initial transverse wall structure whereas at a higher depinningfield (> 4 mT), the DW is depinned with a transformation of the inner structure with an antivortexsoon after the DW has escaped from the notch due to the Walker breakdown phenomenon. Veryinterestingly, with any external field, the depinned DW with antivortex inner structure is observedto move back to the original notch position. This is explainable because the notch acts as anattractive pinning potential for the DW.
D. Djuhana,L. Rohman,D. H. Kim 한국자기학회 2017 Journal of Magnetics Vol.22 No.3
In this study, we have systematically calculated the dynamic susceptibility spectra of LSMO (La0.7Sr0.3MnO₃) ferromagnetic nanopillars by means of a micromagnetic simulation. Simulation has been carried out for LSMO nanopillars consisted of disk and square shapes with respect to the height variation. The diameter of disk pillar and the length of square pillar were fixed to be 50 nm and the height of pillar were varied from 100 to 500 nm with increment of 50 nm. The exponential type magnetic pulses have been applied in the long axis and perpendicular to the initial spin configuration of the pillars. The dynamic susceptibility spectra of the pillar were determined by fast Fourier transform (FFT) based on the magnetization response. We have obtained the resonance frequency of the pillars from the imaginary part of the dynamic susceptibility spectra. Interestingly, the resonance frequency peak of the nanopillars increased as the height increased and followed the Kittel’s resonance formula. It was found that the demagnetization energy from dipolar interaction mainly contributed to the frequency resonance of the nanopillars.
Suppression of Magnetization Ringing After Domain Wall Collision Studied by Micromagnetic Simulation
Dede Djuhana,Hong-Guang Piao,Sang Hyuk Lee,Su-Hyeong Jun,Je-Ho Shim,Dong-Hyun Kim 한국자기학회 2008 Journal of Magnetics Vol.13 No.4
Magnetization ringing following domain wall collision on a ferromagnetic nanowire has been investigated by micromagnetic simulation. Suppressed magnetization ringing is observed with the introduction of a small ribbon to the nanowire. Magnetization ringing has been analyzed in a frequency space by a fast Fourier transform. With the introduction of a small ribbon and/or taping of the wire, the amplitude of ringing is reduced with a shifted frequency peak.
Kurniawan Candra,Djuhana Dede,Soegijono Bambang,Kim Dong-Hyun 한국물리학회 2021 Current Applied Physics Vol.27 No.-
We report our micromagnetic simulations based on Landau-Lifshitz-Gilbert (LLG) equation for CoFeB nanowire which was exposed by sub-nanosecond magnetic pulse with varied pulse width between 100 and 1000 ps. It is found that the Walker Breakdown field (HWB) shifted as the field pulse duration decreased and reached at the highest value in case of 100 ps pulse width, then decreased steeply with respect to the pulse width up to 400 ps. HWB values are not significantly dependent for pulses longer than 500 ps. It is observed that, below the HWB, the exchange energy is larger than the demagnetization energy in the wider nanowire. By energy density analysis, it is understood that the increase of HWB values in the cases of narrower pulse width was to compensate the energy needed to move the DW.