Micromagnetic Simulation of CNT-MFM Probes under Magnetic Field

Takashi Manago,Hironori Asada,Hiromi Kuramochi 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12

On the ferromagnetic-film-coated carbon nanotube for a magnetic force microscope (CNT-MFM)probe, the stability of the magnetic structure in an external magnetic field was investigated usinga three-dimensional micromagnetic simulation. When a magnetic field was applied along the longitudinaldirection, in the direction opposite that of the magnetization of the probe, the directionof the magnetic moments of the probe remained the same up to –200 mT and then reversed all atonce. When a magnetic field was applied along horizontal direction, the direction of the magneticmoments gradually tilts with increasing field. MFM observations seem to be possible for magneticfields up to 100 150 mT, judging from the magnetic structure of the probe. In contrast, themagnetic structures of pyramidal probes show vortex-like magnetic structure and low tolerance toan external magnetic field. The CNT-MFM probe is relatively robust under an external magneticfield due to the strong shape anisotropy attributed to its cylindrical shape.

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.

Micromagnetic Simulations for Spin Transfer Torque in Magnetic Multilayers

Chun-Yeol You 한국자기학회 2012 Journal of Magnetics Vol.17 No.2

We investigate spin transfer torque (STT) in magnetic multilayer structures using micromagnetic simulations. We implement the STT contribution for magnetic multilayer structures in addition to the Landau-Lifshitz-Gilbert (LLG) micromagnetic simulators. In addition to the Sloncewski STT term, the zero, first, and second order field-like terms are also considered as well as the effects of the Oersted field due to the running current are addressed. We determine the switching current densities of the free layer with the exchange biased synthetic ferrimagnetic reference layers for various cases.

Magnetization Dynamics Modeling in a Like Iron-Silicon Thin Film by the Micromagnetic Approach

Messaoud Boufligha,Lakhdar Bessissa,Djillali Mahi 한국자기학회 2023 Journal of Magnetics Vol.28 No.3

Iron-silicon thin films used as a single layer or in sandwich structures are currently regarded as a promising candidate in high magnetic sensors. A detailed understanding of magnetization dynamics in such thin films is of great interest. In this work, we only focused on modeling the magnetization reversal. Numerical solution to the nonlinear Landau-Lifshitz-Gilbert (LLG) equation can be used to conduct the study. With the help of our developed Matlab code, the simulations were carried out. External field strength, damping parameter and temperature all have an impact on the speed of the magnetization reversal. The validation of our computations is achieved via a separate simulation. It relates to the solution of the standard problem proposed by the micromagnetic Modeling Activity G roup (μMAG ). T he r esults are in agreement with the ones presented in the National Institute of Standards and Technology (NIST) website.

Spin-polarized Current Switching of Co/Cu/Py Pac-man type II Spin-valve

Andrew Lyle,Yang-Ki Hong,Byoung-Chul Choi,Gavin Abo,Seok Bae,Jeevan Jalli,Jae-jin Lee,Mun-Hyoun Park,Ryan Syslo 한국자기학회 2010 Journal of Magnetics Vol.15 No.3

We investigated spin-polarized current switching of Pac-man type Ⅱ (PM-Ⅱ) nanoelements in Pac-man shaped nanoscale spin-valves (Co/Cu/Py) using micromagnetic simulations. The effects of slot angle and antiferromag-netic (AFM) layer were simulated to obtain optimum switching in less than 2 ns. At a critical slot angle of 105˚, the lowest current density for anti-parallel to parallel (AP-P) switching was observed due to no vortex or antivortex formation during the magnetic reversal process. All other slot angles for AP-P formed a vortex or antivortex during the magnetization reversal process. Additionally, a vortex or anti-vortex formed for all slot angles for parallel to anti-parallel (P-AP) switching. The addition of an AFM layer caused the current density to decrease significantly for AP-P and P-AP at slot angles less than 90˚. However, at slot angles greater than 90˚, the current density tended to decrease by less amounts or actually increased slightly as shape anisotropy became more dominant. This allowed ultra-fast switching with 5.05 and 5.65 x 10? A/㎠ current densities for AP-P and P-AP, respectively, at a slot angle of 105˚.

Metastable Vortex State of Perpendicular Magnetic Anisotropy Free Layer in Spin Transfer Torque Magnetic Tunneling Junctions

Chun-Yeol You,Hyungsuk Kim 한국자기학회 2013 Journal of Magnetics Vol.18 No.4

We find a metastable vortex state of the perpendicular magnetic anisotropy free layer in spin transfer torque magnetic tunneling junctions by using micromagnetic simulations. The metastable vortex state does not exist in a single layer, and it is only found in the trilayer structure with the perpendicular magnetic anisotropy polarizer layer. It is revealed that the physical origin is the non-uniform stray field from the polarizer layer.

Dynamics of Transverse Magnetic Domain Walls in Rectangular-shape Thin-film Nanowires Studied by Micromagnetic Simulations

Jun-Young Lee,Sangkook Choi,Sang-Koog Kim 한국자기학회 2006 Journal of Magnetics Vol.11 No.2

Dynamic behaviors of transverse domain walls (TDWs) in rectangular shaped thin-film magnetic nanowires with different widths under applied magnetic fields less than the Walker field were studied by micromagnetic simulations. It was found that the velocity of stable TDWs in the viscous region increases from 147 to 419 ㎧ and their mass decreases from 6.24 × 10?²³ to 2.70 × 10?²³ ㎏ with increasing strength of the applied magnetic field ranging from 5 to 20 Oe for the nanowire with a dimension of 10 ㎚ in thickness and 5 ㎛ in length, and 50 ㎚ in width. With increasing the width of nanowires from 50 to 125 ㎚ at a specific field strength of 5 Oe, the TDW’s velocity also increases from 147 to 246 ㎧ and its mass decreases from 6.24 × 10?²³ to 5.91 × 10?²³ ㎏.

강자기 소용돌이의 단조화 운동 유도 및 수치 검증

김준연(Junyeon Kim),최석봉(Sug-Bong Choe) 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.4

We report a theoretical description of ferromagnetic vortex motion in sub-micrometer size magnetic thin film. Based on Thiele's equation combined with later theoretical achievements, we derive the analytic description of dynamics of ferromagnetic vortex core as a damped harmonic oscillatory motion. Consequently, the relations about frequency and damping constant in damped harmonic oscillation are presented. The validity of the results is verified through micromagnetic simulation.

Field-controllable injection of virtual magnetic domainwall in discrete magnetic nanodot chains

Xiao-Ping Ma,김선대,PIAO HONGGUANG,김동현 한국물리학회 2018 Current Applied Physics Vol.18 No.1

Periodic injection behaviors of virtual magnetic domain wall (VDW) have been systematically investigated in asymmetrically shaped nanodot chains by means of micromagnetic simulations. Systematic investigation on a controllable VDW injection has been carried out. We demonstrate that precise control of VDW injection is achievable by using different nanodot shapes as well as by changing alternating magnetic field (AC field) profiles. The VDW position can be tuned by adjusting AC field frequency and amplitude. Field-controllable periodic VDW injection phenomenon is found to be sustainable over wide ranges of phase diagram spanned by AC field frequency and amplitude.

Embedded Object-Oriented Micromagnetic Frame (OOMMF) for More Flexible Micromagnetic Simulations

Hyungsuk Kim,Chun-Yeol You 한국자기학회 2016 Journal of Magnetics Vol.21 No.4

We developed an embedded Object-Oriented Micromagnetic Frame (OOMMF) script schemes for more flexible simulations for complex and dynamic mircomagnetic behaviors. The OOMMF can be called from any kind of softwares by system calls, and we can interact with OOMMF by updating the input files for next step from the output files of the previous step of OOMMF. In our scheme, we set initial inputs for OOMMF simulation first, and run OOMMF for Δt by system calls from any kind of control programs. After executing the OOMMF during Δt, we can obtain magnetization configuration file, and we adjust input parameters, and call OOMMF again for another Δt running. We showed one example by using scripting embedded OOMMF scheme, tunneling magneto-resistance dependent switching time. We showed the simulation of tunneling magneto-resistance dependent switching process with non-uniform current density using the proposed framework as an example.