• Title, Summary, Keyword: magnetic wall

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Current Density and Thickness Effects on Magnetic Properties of Electrodeposited CoPt Magnetic Films

  • Kim, Hyeon Soo;Jeong, Soon Young;Suh, Su Jeong
    • Journal of Magnetics
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    • v.18 no.4
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    • pp.417-421
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    • 2013
  • The dominant magnetization reversal behavior of electrodeposited CoPt samples with various thicknesses deposited at different current densities was the domain wall motion by means of wall pinning. The magnetic interaction mechanism was dipolar interaction for all samples. The dipolar interaction strength was significantly affected by the sample thickness rather than by the current density, while the magnetic properties were closely related to the current density.

Micromagnetic Analysis of Thermal Magnetization Fluctuations in Ferromagnetic Nanowires (미세자기 동역학을 이용한 강자성 나노선의 자기 잡음 연구)

  • Yoon, Jung-Bum;You, Chun-Yeol;Jo, Young-Hun;Park, Seung-Young;Jung, Myung-Hwa
    • Journal of the Korean Magnetics Society
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    • v.20 no.1
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    • pp.1-7
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    • 2010
  • We investigate the spin dynamics of the magnetic domain wall using the magnetic noise in the magnetic nanowire structure by employing micromagnetic simulations. Magnetic noise due to the thermal fluctuations in ferromagnetic materials is related to magnetic susceptibility and resonance frequency, which are important physical quantities in the study of the spin dynamics. In this study, we present the magnetic noise of the single domain without magnetic domain wall, and with the magnetic domain wall between two magnetic domains in ferromagnetic nanowires. It is confirmed that the Kittel equation with simple ellipsoid model with demagnetizing factor well describe the resonance frequency due to magnetic noise of the single domain. Besides, we find that there is a distinguishable additional resonance frequency, when a magnetic domain wall exists. It is verified that the additional resonance frequency is originated from the magnetic domain wall, and it is lower than one of the single domain. It implies that the spins inside the domain wall have a different effective field.

Domain Wall Motions in Ferromagnetic Thin Film Induced by Laser Heating Pulse

  • Park, Hyun Soon
    • Applied Microscopy
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    • v.48 no.4
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    • pp.128-129
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    • 2018
  • Soft ferromagnetic materials are utilized for various electromagnetic devices such as magnetic recording heads and magnetic shielding. In situ observation of magnetic microstructures and domain wall motions are prerequisite for understanding and improving their magnetic properties. In this work, by the Fresnel (out-of-focus) method of Lorentz microscopy, we observe the domain wall motions of polycrystalline Ni/Ti thin film layers triggered by single-shot laser pulse. Random motions of domain walls were visualized at every single pulse.

Simulation of the Effect of Soft Underlayer Domain Wall Structure on Output Signal in Perpendicular Magnetic Recording

  • Kim, Eun-Sik;Lim, Chee-Kheng;Kim, Yong-Su;Lee, Ju
    • Journal of Magnetics
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    • v.11 no.2
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    • pp.83-86
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    • 2006
  • Controlling magnetic domains in soft underlayer (SUL) of perpendicular magnetic recording (PMR) is an important issue for the application of PMR in HDD. We studied the magnetic domain structures in SUL using the finite element based micromagnetic simulation (FEMM) for the SUL models with different thicknesses. The purpose is to simulate the magnetic domain wall noise when the SUL thickness and saturation magnetization are changed. The simulation results show that a 15 nm SUL forms simpler Neel wall domain wall pattern and 40 nm SUL forms complex Bloch wall. To visualize the effect of these domain walls stray field at a read sensor position, the magnetic stray field of the domain walls at air bearing surface (ABS) which is 50 nm above the SUL was simulated and the results imply that Bloch walls have stronger stray field with more complicated field patterns than Neel walls and this becomes a significant noise source. Therefore, the thickness of the SUL should be controlled to avoid the formation of Bloch walls.

Current-Induced Magnetic Domain-Wall Motion by Spin Transfer Torque: Collective Coordinate Approach with Domain-Wall Width Variation

  • Jung, Soon-Wook;Lee, Hyun-Woo
    • Journal of Magnetics
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    • v.12 no.1
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    • pp.1-6
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    • 2007
  • The spin transfer torque generated by a spin-polarized current can induce the shift of the magnetic domain-wall position. In this work, we study theoretically the current-induced domain-wall motion by using the collective coordinate approach [Gen Tatara and Hiroshi Kohno, Phys. Rev. Lett. 92, 86601 (2004)]. The approach is extended to include not only the domain-wall position and the polarization angle changes but also the domain-wall width variation. It is demonstrated that the width variation affects the critical current.

A Study on the Flow Analysis for Natural Convection of Magnetic Fluid in a Cubic Cavity (밀폐공간내 자성유체의 유동특성에 관한 연구)

  • Ryu, Shin-Oh;Park, Joung-Woo;Seo, Lee-Soo
    • Proceedings of the KSME Conference
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    • pp.142-147
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    • 2001
  • Natural convection of a magnetic fluid is different from that of Newtonian fluids because magnetic body force exists in an addition to gravity and buoyancy. In this paper, natural convection of a magnetic fluids(W-40) in a cubic cavity is examined by numerical and experimental method. One side wall was kept at a constant temperature($25^{\circ}C$), and the opposite side wall was also held at a constant but lower temperature($20^{\circ}C$). Under above conditions, various magnitudes of the magnetic fields were applied up. GSMAC scheme is used for a numerical method, and the thermo-sensitive liquid crystal film(R20C5A) is utilized in order to visualize wall-temperature distributions as an experimental method. This study has resulted in the following fact that the natural convection of a magnetic fluids is controlled by the direction and intensity of the magnetic fields.

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Guideline for the Design of Wall-Climbing Mobile Robot Using Permanent Magnetic Wheels (영구 자석 바퀴를 이용한 벽면 이동 로봇의 설계시의 설계지침)

  • 이화조;김은찬;한승철
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.548-553
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    • 2002
  • Most tasks of the large vertical or ceiling structures have been carried out by human power. Those tasks require us much operation costs and times, safety devices, etc. So the need of automation for those tasks have been rising. That automation needs a wall-climbing mobile vehicle. Most former researches are things about attachment devices and moving mechanisms. A wall-climbing mobile vehicle must be designed by a method different from the case of the vehicle of the horizontal environment. That is because gravity acts as a negative role on the stability of a wall-climbing vehicle. In this thesis, the particular shape characteristics of a wall-climbing mobile vehicle are derived by the wall-environment modeling. In addition, some design constraints of the permanent magnetic wheel as an attachment device was studied. According to those requirements and constraints, one specific wall-climbing mobile vehicle was designed and some experiments were made on the attachment ability of that vehicle.

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A Study on the Flow Behavior of Magnetic Fluids in a half Circular Pipe (반원관내 자성유체의 자연대류에 관한 연구)

  • Hwang, Sung-Wook;Park, Joung-Woo;Seo, Lee-Soo
    • Proceedings of the KSME Conference
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    • pp.3098-3103
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    • 2007
  • In this paper, natural convection of a magnetic fluids(W-40) in a half circular pipe enclosure are investigated by numerical and experimental method. One side wall is kept at a constant temperature(25$^{\circ}C$), and the opposite side wall is also kept at a constant temperature(20$^{\circ}C$). Under above conditions, various magnitudes of the magnetic fields were applied up. Theoretical study through the governing equation derived by Siliomis is carried out with numerical analysis by the GSMAC Method. And the thermo-sensitive liquid crystal film(R20C5A) is utilized in order to visualize wall-temperature distributions as an experimental method. This study has resulted in the following fact that the natural convection of a magnetic fluids are controlled by the direction and intensity of the magnetic fields.

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A Study On The Propagation Failure Modes of Ion Implanted Magnetic Bubble Computer Memory Devices (이온주입식 자기버블 전산기 기억소자에서의 자기버블 전파실패에 관한 연구)

  • Jo, Soon-Chul
    • Proceedings of the KIEE Conference
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    • pp.339-342
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    • 1988
  • Typical magnetic bubble propagation failure modes of ion implanted magnetic bubble computer memory devices were observed and their failure mechanisms were analize. The skidding failure mode is due to the pushing of a strong repulsive charged wall. If this pushing is stronger than the edge affinity of the bubble in the cusp, the bubble moves out of the cusp when it is supposed to stay there. The stripeout failure modes across the adjacent track or along the track can be explained by considering the relative strength of the charged wall and the edge affinity encountered by both ends of the stripe. The skipping of the first cusp of a track is believed to be due to the whipping motion of the charged wall. The bubble moves directly to the second cusp via the long charged wall pointing to the second cusp skipping the first cusp.

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A Modelling of magnetization reversal characteristics in magneto-optic memory system (광자기 기억장치에서의 자화반전 특성 모델링)

  • 한은실;이광형;조순철
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.19 no.10
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    • pp.1849-1860
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    • 1994
  • Domain wall dynamics in thin film of amorphous Rare Earth-Transistion Metal alloys were investigated using numerical integration of the Landau-Lifshitz-Gilbert equation. The thin film was divided into a two-dimensional square lattice ($30\times30$) of dipoles. Nearest-neighbor exchange interaction magnetic anisotropy, applied magnetic field, and demagnetiing field of interacting anisotropy, applied magnetic field, and demagnetizing field of interacting dipoles were considered. It was assumed that the film had perfect uniaxial anisotropy in the perpendicular direction and the magnetization reversal existed in the film. The time of domain wall creation and the thickness of the wall were investigated. Also the motion of domain walls under an applied field was considered. Simulation results showed that the time of domain wall creation was decreased significantly and the average velocity of domain wall was increased somewhat when the demagnetizing field was considered.

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