1,721,027 research outputs found
Analytic description of the magnetization-reversal phase diagram in thin films with uniaxial perpendicular magnetic anisotropy
No full textWe present an analytic description of magnetization-reversal phases based on a micromagnetic theory. Calculated phase diagrams characterize three contrasting domain evolution patterns: wall-motion, dendritic-growth, and nucleation dominant phases. Gradual phase transitions are observed with respect to the magnetostatic energy, the domain-wall energy, and the temperature, while minor phase shifts are seen with respect to the anisotropy, the cell volume, the applied field, and the simulation size. Variation in the local anisotropy of only a few percent induces phase transitions.This work was supported by the Korean Ministry of Science
and Technology through the Creative Research Initiatives
Project
Phase diagram of three contrasting magnetization reversal phases in uniaxial ferromagnetic thin films
No full textWe present an analytical description of a magnetization reversal phase diagram of ferromagnetic thin films that have uniaxial perpendicular anisotropy. The phase equilibrium lines were calculated from a micromagnetic consideration of equilibrium conditions of the wall motion, dendritic growth, and nucleation processes. The phase diagram characterizes well simulated domain evolution patterns: typical domain evolution patterns are predicted accurately in the corresponding phases accompanied by gradual phase transitions across the phase equilibrium lines. (C) 2002 American Institute of Physics.This work was supported by the Korean Ministry of Science
and Technology through the Creative Research Initiative
Project
Magnetization reversal in Co/Pd multilayers with varying Co sublayer thickness
No full textWe have investigated magnetization reversal in nanostructured Co/Pd multilayers. Interestingly enough, reversal phenomena in this system were found to be very sensitive to the Co-sublayer thickness and very contrasting reversal behaviors were observed between the samples having 2-Angstrom-thick Co and 4-Angstrom-thick Co sublayers. Direct domain observation and time-dependent magnetization viscosity curves revealed the wall-motion dominant reversal in the former samples, and the nucleation dominant reversal in the latter samples. Magnetization reversal in Co/Pd multilayers was theoretically studied by Monte Carlo simulation and experimentally observed reversal behaviors could be well explained. (C) 1997 American Institute of Physics.This work was supported by the Korea Science and En-
gineering Foundation under Grant No. 941-0200-031-02 and
the Ministry of Science and Technology of Korea
Domain reversal simulation for anisotropy-energy fluctuation
No full textInfluence of a nonuniform anisotropy distribution on domain reversal dynamics in ferromagnetic thin films has been investigated. A micromagnetic model has been developed adopting a Monte Carlo algorithm to examine the thermally activated reversal process. In this study, the uniaxial magnetic anisotropy magnitude is spatially nonuniform, Interestingly, the simulation results demonstrate the crucial importance of the nonuniform anisotropy variation on the domain reversal dynamics, The reversal behavior is altered from wall-motion dominant to nucleation dominant with a small change in the spatial anisotropy distribution
Direct observation of non-Gaussian distribution of local magnetic properties in ferromagnetic thin films
No full textWe report our experimental finding that magnetic properties of Co-based multilayer films are shown to exhibit their local variations far from the Gaussian (or Lorentzian) distribution which are usually assumed. The local variations of the coercivity and the field dependence lambda(=-partial derivativeln tau/partial derivativeH) were determined from measurements of the hysteresis loop and the field-dependent switching time tau, respectively, on spatially resolved local regions 400 nm in size by means of a magneto-optical microscope magnetometer. We show that the two local magnetic properties inversely correlate with each other and a thermally activated process takes place during magnetization reversal on a submicrometer scale in ferromagnetic thin films.This work was supported by the Korean Ministry of Science
and Technology through the Creative Research Initiatives
Project
Quantitative analysis on correlation between local coercivity and reversal time in ferromagnetic thin films
No full textWe report a method to quantitatively analyze the correlation between the local coercivity variation and the local reversal-time distribution in ferromagnetic thin films. The spatial distribution of the local coercivity on a film plane was directly measured from the hysteresis loops of each local area of 320x320 nm(2) and then, the local coercivity distribution was quantitatively correlated with the local reversal-time distribution obtained from time-resolved domain evolution patterns grabbed at precisely the same position of the film. We demonstrate a clear experimental evidence of the direct correlation between the real coercivity distribution and the magnetization reversal dynamics, which could be explained within a context of a thermally activated relaxation process. (C) 2000 American Institute of Physics. [S0021-8979(00)07718-5].This work was supported by the Creative Research Initiatives
of the Ministry of Science and Technology of Korea
Spatial mapping of activation magnetic moment in ferromagnetic films
No full textWe report a technique to simultaneously determine the local activation magnetic moment with a spatial resolution of a submicrometer scale. The local activation magnetic moment is determined from the magnetic-field dependence of the magnetization reversal at the corresponding region observed by a magneto-optical microscope system. The present method has been applied to measure the activation magnetic moment distribution of Co/Pd multilayers. It was found that the activation magnetic moment was nonuniform on a submicrometer scale and that the distribution of the activation magnetic moment enhanced with increasing the film thickness. (C) 2001 American Institute of Physics.This work was supported by the Ministry of Science and
Technology of Korea through the Creative Research Initiatives
Project
Observation of unequal activation volumes of wall-motion and nucleation processes in Co/Pd multilayers
No full textWe report the difference in activation volumes of wall-motion and nucleation processes in Co/Pd multilayers. Each activation volume was estimated from field dependence of wall-motion speed and nucleation rate, obtained by real-time domain imaging using a magneto-optical Kerr effect microscope. Delicate analysis shows that the two activation volumes are generally unequal and the ratio between the volumes varies noticeably from 0.9 to 1.1 with change of the multilayered structure. We found that the inequality in the two activation volumes has a crucial influence on magnetization reversal behavior: a process having a smaller activation volume dominates.This work was supported by the Creative Research
Initiatives of the Ministry of Science and Technology
of Korea
Domain configurations and reversal dynamics in Co-based nanomultilayers
No full textDomain configurations and reversal behaviors in Go-based nanomultilayers have been quantitatively investigated. A sharp transition of domain configuration from a large area domain pattern to a striped domain configuration with increasing the Go-sublayer thickness has been experimentally observed, The transition was well explained by an analytic theory based on calculating the magnetostatic energy in the multilayered structure by solving Maxwell's equations in continuum approximation. The transition was found to be ascribed to a competition between the magnetostatic energy and the domain-wall energy. Magnetization reversal dynamics ire Co-based nanomultilayers has been investigated by the magnetization viscosity measurement and the real-time domain observation. The reversal behaviors were sensitively changed from wall-motion dominant to nucleation dominant with either increasing the Co-sublayer thickness or increasing the number of repeats. Quantitative analysis revealed that the contrasting reversal behavior was mainly caused by the sensitive change in the wall-motion speed. The reversal ratio of the wall-motion speed to the nucleation rate was found to be an important parameter to characterize the reversal behavior in these systems.This work was supported by the Creative Research Initiatives of Ministry
of Science and Technology of Kore
Complete magnetizing field relating with magnetization reversal dynamics
No full textWe report the experimental finding that a complete magnetizing field Hm, exists in magnetization reversal dynamics of ferromagnetic thin films, which is much larger than the apparent magnetic saturation field measured from the major hysteresis loop. Magnetization reversal dynamics contrastingly changes from nucleation dominated to wall-motion dominated according to an initial magnetization state magnetized by a field below H-M, whereas it is basically unchanged when the field is larger than Hm. The complete magnetizing field is found to be 1.5-2.0 times larger than the apparent magnetic saturation field and 6-10 times smaller than the anisotropy field in Co/Pd multilayer thin films. (C) 2001 Elsevier Science B.V. All rights reserved.This work was supported by the Korean
Ministry of Science and Technology through the
Creative Research Initiatives Project
- …
