• Current Applied Physics
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• v.18 no.11
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• pp.1185-1189
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• 2018

Thickness-dependent magnetic domain structure of ultrathin Co wedge films (0.3 nm-1.0 nm) sandwiched by Pt layers was investigated by scanning transmission x-ray microscopy (STXM) employing X-ray magnetic circular dichroism (XMCD), utilizing elliptically polarized soft x-rays and electromagnetic fields, with a spatial resolution of 50 nm. The magnetic domain images measured at the Co $L_3$ edge showed the evolution of the magnetic domain structures from maze-like form to the bubble-like form as the perpendicular magnetic field was applied. The asymmetric domain expansion of a 500 nm-scale bubble domain was also measured when the in-plane and perpendicular external magnetic field were applied simultaneously.

• Journal of the Korean Magnetics Society
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• v.27 no.1
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• pp.35-40
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• 2017

Kerr microscopy was assembled to observe magnetic domain image of ultra thin 3 %Si-Fe by using parts of an optical microscope. Digital images were obtained from CCD camera attached to the microscopy. A method was suggested to decide a boundary between magnetic domain regions in this study. The method was using some operations such as subtraction, integration and least mean square approximation for pixel values in the digital image. The method has a strong point that high priced image processor is not needed in the Kerr microscopy system. From the results that three different domain walls were observed and magnetic flux density of 0.085 [T], this method could be applied in the magnetic domain regions having a straight $180^{\circ}$ domain wall.

• 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.

• 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.

• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.305-308
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• 2008

In this paper, the magnetic domain states and recordability of the molded magnetic nanopillars were examined and analyzed by magnetic force microscopy (MFM) measurement. We focused on the some of the technical issues for MFM measurement regarding the lift height and geometry of the MFM tip. The effects of MFM tip shape and lift height on the MFM resolution were analyzed. Finally, we showed that the magnetic film on each molded nanopillars has a single magnetic domain state.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.681-684
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• 2015

Magnetization is very important in the ferro-magnetic physics and provides useful informations in the application field of magnetic devices. Generally, the only first acquired domain pattern is not helpful to recognize domain pattern. Many images are needed to visualize domain pattern through image processing. These images were obtained a 8-bit digital camera. The operation was the subtraction of pixel values of multi domain imanges from the images with 255 of pixel value, which was obtained in the saturated state of magnetic materials. The magnetic domain images was visualized gradually with increasing the number of subtracion operation. LABVIEW was used as an image processing tool and the optic microscope with a polarizer was used in this experiment.

• Journal of Magnetics
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• v.17 no.4
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• pp.242-244
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• 2012

We report on the basis of experiments that magnetic domain structures exhibit a transition between single and dendrite domains with respect to the width of ferromagnetic nanowires. This transition is directly observed in CoFe/Pt multilayered nanowires having a width in the range of 580 nm to 4.2 ${\mu}m$ with a magnetic force microscope. Nanowires wider than 1.5 ${\mu}m$ show typical dendrite domain patterns, whereas the nanowires narrower than 690 nm exhibit single domain patterns. The transition occurs gradually between these widths, which are similar to the typical widths of the dendrite domains. Such a transition affects the strength of the domain wall propagation field; this finding was made by using a time-resolved magneto-optical Kerr effect microscope, and shows that the domain wall dynamics also exhibit a transition in accordance with the domain configuration.

• Korean Journal of Materials Research
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• v.14 no.2
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• pp.94-100
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• 2004

We have investigated the magnetic domain structure and the thermal stability of magnetotransport properties of IrMn biased spin-valves containing Co, CoFe and NiFe. The magnetic domain structures were imaged using a magneto-optical indicator film(MOIF) technique. To investigate the thermal stability, magnetoresistance(MR) was measured at annealing temperature(TANN) and room temperature($T_{RT}$) followed by the annealing. Domain imaging reveal that the increase of annealing temperature led to changes in the exchange coupling between the two ferromagnet(FM) layers through nonmagnetic layer rather than between FM and antiferromagnet. unlike the NiFe biased IrMn spin valve with large domains, MOIF pictures of Co and CoFe biased IrMn spin valve structures show the formation of many small microdomains. The magnetic structure, as revealed by the domain images, appeared unchanged while the MR dropped dramatically. From the combined giant magnetoresistance(GMR) and MOIF results, it was apparent that the decrease of MR ratio was not related to the spin valve magnetic structure up to about $350^{\circ}C$($T_{RT}$ ).

• Journal of Magnetics
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• v.15 no.3
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• pp.99-102
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• 2010

We present the fractal properties of the magnetic domain walls in $(5-{\AA}\;Co_{90}Fe_{10}/10-{\AA}\;Pt)_n$ multilayer films with perpendicular magnetic anisotropy for the number of repeats n (1 to 5). In these films, the magnetization reversed due to the domain wall propagation throughout the films with rare nucleations. As n increased, it was observed that the jaggedness of the domain walls increased noticeably, which is possibly due to the accumulation of irregularities at the layer interfaces. The jaggedness of the domain walls was analyzed in terms of the fractal dimension by use of the ruler method, and it was revealed that the fractal dimension significantly changed from $1.0{\pm}0.002$ to $1.3{\pm}0.05$ as n increased from 1 to 5.