L-형 강자성체 나노선의 두께 변화에 따른 자구벽 동역학 시뮬레이션

박홍광,주하나 데데,이상혁,심제호,전수형,김동현 한국물리학회 2009 새물리 Vol.58 No.6

마이크로자성 시뮬레이션을 통하여 L-형 강자성체 나노선의 두께 변화에 따른 자구벽운동을 연구하였다. 외부자기장이 5 mT인 조건하에 나노선의 두께를 2.5 nm로부터 10 nm까지 변화시키면서 자구벽의 운동 및 운동과정 중 자구벽내의 마이크로스핀구조가 어떻게 변하는가를 관찰하였다. 자구벽은 횡단형과 반소용돌이형의 두자기 구조를 가지고 운동하며, 두가지 스핀구조는 자구벽의 운동과정 중 주기적으로 나타났다. 이러한 스핀구조 변화에 따라 자구벽은 앞뒤로 진동하면서 이동하였다. 자구벽의 평균 이동속도는 나노선의 두께가 얇아지면서 더 빨라졌지만, 자구벽의 진동주기는 거의 변화를 보이지 않았다. We investigated the dynamics of magnetic domain wall propagating along a nanowire. The magnetic domain wall exhibited a transitional behavior between a transverse- and an antivortex-type wall spin structure during propagation under an external field of 5 mT. Thickness of the nanowire was changed from 2.5 to 10 nm, and we found that the average domain wall speed became faster for a thinner wire, but the oscillation period did not exhibit any meaningful change.

사인곡선형 강자성체 나노선의 자구벽운동 감쇠진동 현상마이크로 자성시뮬레이션

박홍광,데데주하나,이상혁,심제호,전수형,김동현 한국자기학회 2009 한국자기학회 학술연구발표회 논문개요집 Vol.2009 No.12

환기용 축류팬의 가이드핀 블레이드 형상변화에 따른 유동특성에 관한 연구

박홍광(Hongkwang Park),이지근(Jeekeun Lee),노병준(Byungjoon Rho) 대한설비공학회 2007 설비공학 논문집 Vol.19 No.12

The effects of a guide fin blade on the flow characteristics in a ventilating axial fan were investigated experimentally. The guide fins were setup onto the pressure surface of the blade, and their effects on the flowrate were evaluated. Two types of the guide fin blade were designed. One is the stem fin blade, and the other is the radial fin blade. The stem fin is designed normal to the circumference of a circle, and the radial fin is designed along the circumference of a circle. The results from the guide fin blade fans are compared with that of the blade without guide fins. The position and the geometry of the radial fin setting up on the blade have an effect on the increase of flowrate with the minor sacrifice of rotational speed of the blades. The radial fin positioning at 0.84 times blade diameter shows highest performance in the flowrate. The increase of the blade weight resulting from applying the guide fins shows minor effect on the variation of rotational speed of the blades.

Seam Blade의 개발을 위한 성능시험평가

박홍광(H. K. Park),노병준(B. J. Rho),이지근(J. K. Lee),조민호(M. H. Cho) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-

An experimental performance test has been carried out to improve a new blade with higher performance. Most of blades of the fan are designed to be a seamless and simple type, and the flow momentum can generally be evaluated to be comparatively low. Because some portions of the blowing winds can easily be passed through the seamless sharp edge of the blade, and several results studied on these problems have been reported: on the simple blade with edge-line seam, on the simple blade with guide seam. However the results do not show the remarkable increasement of performance of the blades. In this experimental performance test of the blades the design techniques of the blades with double seams (stem seam and edge seam) and comparison tests have been focused. As a first step the comparisons of velocity distributions and flow-rates depending upon the blade are presented in this paper.

다이아몬드형 강자성체의 종횡비 변화에 따른 스핀기저상태의 마이크로자성시뮬레이션

김동현,박홍광,유성초,오석근,주하나데데 한국물리학회 2008 새물리 Vol.57 No.1

We investigated the transitional behavior of the spin ground state for diamond-shaped ferromagnets with a systematic variation of the aspect ratio by means of a micromagnetic simulation. With changing aspect ratio from 1 : 6 to 1 : 1, the spin ground state was observed to a exhibit a transition from a flux-closure to a single-domain state. Repeated simulations for various aspect ratios between 1 : 3 to 1 : 2 produced two states, regardless of the initial spin condition. A detailed analysis was made around the transitional region where the spin configuration changed from a simple single-domain state to a 4-domain Landau state with a magnetic vortex at the center. We further analyzed the magnetic energies of two possible states working as two potential wells in the magnetic energy landscape. 마이크로자성 시뮬레이션을 통해 다이아몬드형 강자성체의 종횡비 변화에 따른 스핀기저상태를 연구하였다. 다이아몬드의 종횡비를 1:6으로부터 1:1까지 변화시키면서 외부자기장이 없는 조건하에 스핀이 초기 임의적 상태로부터 출발하여 어떻게 기저상태로 변하는지를 관찰하였다. 종횡비가 작을 경우 단일자구 (single magnetic domain)상태로 되고 비율이 클 경우 자기소용돌이 (magnetic vortex)포함 4-자구 Landau 형태로 배열됨을 반복 시뮬레이션을 통해 확인하였다. 종횡비 변화에 따라 스핀상태가 어떻게 단일자구형으로부터 4-자구형으로 변화되는가를 관찰하며, 변환영역에서 총 자기에너지 변화를 정량적으로 관찰하며 스핀기저상태의 전이과정을 분석하였다.

Thiele 방정식에 기반한 자기보텍스 코어의 자이로벡터 및 감쇄텐서 계산

심제호,박홍광,김동현 한국물리학회 2011 새물리 Vol.61 No.6

A nanopatterned ferromagnetic element with a magnetic vortex spin structure is considered to be a promising future memory device. Magnetic vortex dynamics is known to be well described by the Thiele equation. In this work, we report our study on how to analytically calculate G(the gyrovector) and D(the damping tensor) in the Thiele equation. 자기 보텍스 스핀구조를 갖는 강자성 나노패턴은 미래의 유망한 메모리소자로 주목 받고 있다. 자기 보텍스 코어의 동역학은 Thiele 방정식으로잘 묘사되는 것이 알려져 있다. 본 연구에서는 Thiele 방정식의G (자이로벡터)와 D(감쇄텐서)가 어떤세부적인 계산과정을 통해 나왔는지 밝히고자 한다.

펄스 필드에 의해 여기된 초기 자기 보텍스 운동 동역학

심제호,박홍광,김동현 한국물리학회 2013 새물리 Vol.63 No.6

A nano-patterned ferromagnetic element with a magnetic vortex spin structure can be used as a memory device or a future spintronics device; thus, the reversal mechanism of the magnetic vortex core should be clearly understood before practical applications. In this work, we report our micromagnetic simulation study on the reversal phenomena of a magnetic vortex core under a short-burst magnetic field with the micromagnetic simulation based on Landau-Lifshitz-Gilbert equation. The amplitude of the burst field was varied from 30 to 50 mT, and the pulse duration was varied from 50 to 100 ps. The material parameters of Permalloy were used. The disk's thickness was 5 nm, and the disk's radius was 250 nm. We observed that a vortex core reversal occured on a 100-ps timescale under a short field burst and was initiated by a wide magnetization dip that rapidly evolved until the generation of antivortex cores needed to reverse the original core. 자기 보텍스 스핀구조를 갖는 강자성 나노패턴을 미래의 메모리 소자로이용하려면 자기 보텍스 코어 역전현상의 동역학적 메커니즘 규명이필요하다. 본 연구에서는 강한 펄스 자기장에 의해 자기 보텍스 코어가역전하는 현상을 마이크로자성 시뮬레이션을 통하여 살펴보았다. 시뮬레이션은 Landau-Lifshitz-Gilbert 방정식을 토대로 하고 있다. 펄스자기장의 세기는 30 ~ 50 mT이며, 펄스 유지시간은 50 $\sim$ 100ps이 되도록 조절하였다. 퍼멀로이 물성을 갖는 디스크에 대해서시뮬레이션을 수행하였고 디스크 두께는 5 nm이며, 반경은 250 nm이다. 보텍스 코어 역전현상이 펄스를 가한 후 100 ps 근처의 아주 짧은 시간스케일 내에서 넓은 자화우물이 반코어를 생성하면서 진행될 수 있음을발견하였다.

중국의 자성 및 자성재료 연구그룹 현황

Guangduo Lu,박홍광(Hong-Guang Piao) 한국자기학회 2017 韓國磁氣學會誌 Vol.27 No.6

Recently, one of adjacent countries, China, is poised to grow rapidly in the field of economics and science technology. In this article, by the introduction of major research groups in the field of magnetism and magnetic materials, the current situation of magnetic research in China are analyzed to promote academic exchange and cooperation between China and Korea.

환풍기용 Seam Blade 기본설계 및 시험평가

노병준(B. J. Rho),박홍광(H. K. Park),조민호(M. H. Cho),이지근(J. K. Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.9

The effects of a seam blade on the performance of an axial flow fan, which is widely used in ventilation, were investigated experimentally. The seams were setup onto the pressure surface of the blade. The four blades with edge seam, double stem seam, edge & double stem seam, and seamless were manufactured for the test, and their effects on the flowrate were evaluated. The stem seam onto the blade was designed according to the formula of quadratic curve. Axial velocity distribution and flowrate were measured using a pitot tube, and they were compared at the same condition. In addition, the fan noise and consuming power were compared with commercial products and newly designed blades. The blade with the double stem seam showed highest flowrate among them.

나노디스크에서의 자기 소용돌이 핵의 3차원 동역학 연구

문정환(Jung-Hwan Moon),이경진(Kyung-Jin Lee),김동현(Dong-Hyun Kim),박홍광(Hong-Guang Piao) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.6

Using micromagnetic simulation, we investigated the effect of thickness of a nanodisk on a resonance frequency of vortex gyration. We observed that the resonance frequency increases with increasing thickness in both cases of 2-dimensional (2D) and 3-dimensional (3D) calculation. However, there is a difference in the increasing rate of resonance frequency between 2D and 3D modeling owing to dynamically developed inhomogeneous magnetic texture along the thickness direction of disk in 3D modeling.