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CoFeB/MgO 박막 재료의 열처리에 따른 강자성공명 특성
윤석수(Seok Soo Yoon),김동영(Dong Young Kim) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.1
We have measured the ferromagnetic resonance (FMR) signal in as deposited and 400 ℃ annealed CoFeB/MgO thin film to investigate the annealing effect on magnetic anisotropies and FMR linewidth (?H<SUB>PP</SUB>). The uniaxial anisotropy field (H<SUB>K1</SUB>) was only observed in the as deposited sample. Whereas, in the 400 ℃ annealed sample, the biaxial anisotropy field (H<SUB>K2</SUB>) was additionally observed in accompany with uniaxial anisotropy field (H<SUB>K1</SUB>). The appearance of biaxial anisotropy fields was originated from the crystalline growth of bcc CoFeB(001) from the MgO(001) interface and by the B diffusion during thermal annealing. Also, the ?H<SUB>PP</SUB> of 400 ℃ annealed sample was increased compared with that of as deposited sample, which was due to the broad distribution of the magnetization axis by the biaxial anisotropy.
PHR 센서의 자체 자기장을 이용한 자성 비드 신호 탐지
윤석수(Seok Soo Yoon),김동영(Dong Young Kim),이재훈(Jae-Hoon Lee),김성준(Sung-Joon Kim),김철기(Cheol-Gi Kim) 한국자기학회 2019 韓國磁氣學會誌 Vol.29 No.5
We analyzed the magnetic field dependence of V<SUB>SF</SUB> signal, which second harmonic signal was generated by self-field of planner Hall resistance (PHR) sensor. The V<SUB>SF</SUB> signal was proportional to the product of sensitivity of PHR sensor and self-field. The magnetic field dependence of bead signal detected by V<SUB>SF</SUB> signal showed maximum value at H = 0. The bead signal detected by using the Self-field sensor operated at H = 0 showed linear behavior up to 1/100 bead concentration. Thus, the Self-field sensor can be applied to the external field free biosensor.
CoFe/MnIr 박막에서 MnIr 두께에 따른 교환 결합 특성 분석
윤석수(Seok Soo Yoon),김동영(Dong Young Kim) 한국자기학회 2019 韓國磁氣學會誌 Vol.29 No.5
We analyzed MnIr thickness dependence of exchange bias fields (H<SUB>ex</SUB>) and rotatable anisotropy fields (H<SUB>ra</SUB>) by the ferromagnetic resonance method in 300℃ annealed CoFe/MnIr(t<SUB>AF</SUB>) bilayers. The critical thickness of MnIr was t<SUB>c</SUB> = 3.0 nm, the H<SUB>ex</SUB> as well as H<SUB>ra</SUB> was appeared at t<SUB>AF</SUB> > t<SUB>c</SUB>. It was due to the grain size distribution of the MnIr. The Hex was induced by fixed AF spins of MnIr grains thicker than t<SUB>c</SUB>, while H<SUB>ra</SUB> was induced by rotatable AF spins of MnIr grains thinner than t<SUB>c</SUB>. The exchange coupling field H<SUB>ec</SUB> = H<SUB>ra</SUB> + H<SUB>ex</SUB> did not depend on the MnIr thickness at t<SUB>AF</SUB> > t<SUB>c</SUB>, therefore, we concluded that the exchange coupling energy did not depend on the MnIr thickness at t<SUB>AF</SUB> > t<SUB>c</SUB>.
Cu 코어/Ni<SUB>80</SUB>Fe<SUB>20</SUB> 쉘 복합와이어를 넣은 솔레노이드 코일 인덕터를 이용하는 L/R 오실레이터 기반 지자기 센서
윤석수(Seok Soo Yoon),김동영(Dong Young Kim),최재연(Jae Yeon Choi),이상훈(Sang Hun Lee) 한국자기학회 2019 韓國磁氣學會誌 Vol.29 No.1
In recent, PNI sensor corporation has been released geomagnetic field sensor with high performance. This sensor uses a new principle measuring the period of digital output pulse of L/R oscillator circuit which is connected to the solenoid coil inductor wound on high permeability amorphous wire. In this paper, we design L/R oscillator circuit based on the PNI’s principle and connect the circuit to the solenoid coil inductor containing Cu core/Ni<SUB>80</SUB>Fe<SUB>20</SUB> shell composite wire fabricated by electrodeposition. We investigate applicability of this system to geomagnetic field sensor.
NiFe/MnIr 박막에서 교환 바이어스의 각도 의존성 연구
윤석수(Seok Soo Yoon),김동영(Dong Young Kim) 한국자기학회 2017 韓國磁氣學會誌 Vol.27 No.1
In this report, we calculated the angular dependence of exchange bias (H<SUB>ex</SUB>) by using single domain model in exchange coupled ferromagnetic (F)/antiferromagnetic (AF) bilayers, which results with AF thickness (t<SUB>AF</SUB>) were used for the analysis of measured ones in NiFe/MnIr bilayers. Angular dependence of Hex calculated at t<SUB>AF</SUB> > t<SUB>c</SUB> showed typical unidirectional behaviors, however, calculated one at 0.5t<SUB>c</SUB> < t<SUB>AF</SUB> < t<SUB>c</SUB> showed peculiar angular behaviors by fixed AF spins at specified angle near θ<SUB>H</SUB>= 90°. Angular dependence of H<SUB>ex</SUB> measured in NiFe/MnIr (20 nm) bilayers showed typical unidirectional behaviors. However, measured one in NiFe/MnIr (4 nm) bilayers showed mixed behaviors including both of unidirectional and peculiar angular behaviors, which was explained by the grain size distribution of polycrystalline MnIr.
교환 결합력을 갖는 NiFe/CoFe 박막에서 강자성 공명 신호의 각도 의존성 연구
윤석수(Seok Soo Yoon),김동영(Dong Young Kim) 한국자기학회 2022 韓國磁氣學會誌 Vol.32 No.5
The angular dependence of ferromagnetic resonance signal showed single resonance mode (H<SUB>r</SUB>) at near in-plane (θ<SUB>H</SUB> ≈ 0), and dual resonance modes (H<SUB>r1</SUB> < H<SUB>r2</SUB>) at near normal to plane (θ<SUB>H</SUB> ≈ 90˚) in NiFe(100 ㎚)/CoFe(5 ㎚) thin film, respectively. The single mode H<SUB>r</SUB> was due to effective magnetic properties by the ferromagnetic exchange coupled NiFe/CoFe bilayers. The H<SUB>r1</SUB> of dual mode was same as the ferromagnetic resonance field of the NiFe single layer, and H<SUB>r2</SUB> of dual mode was explained by the ferromagnetic exchange coupling effect.
교환 결합력을 갖는 CoFe/MnIr 박막에서 강자성 공명 선폭의 각도 의존성 연구
윤석수(Seok Soo Yoon),김동영(Dong Young Kim) 한국자기학회 2016 韓國磁氣學會誌 Vol.26 No.2
We analyzed the angular dependence of ferromagnetic resonance linewidth in exchange coupled CoFe/MnIr bilayers. The maximum and minimum linewidth was observed in the easy and hard direction of unidirectional anisotropy by exchange coupling, respectively, and it was well agreed with the angular dependence of exchange bias field. The maximum linewidth was due to the twist of CoFe magnetization near CoFe/MnIr interface from direction of pinned MnIr spin to direction of applied magnetic field. While, minimum linewidth more higher than that of CoFe was related to rotatable anisotropy field, and explained by easy axis distribution of MnIr grains.
평면홀 센서를 이용한 비정질 CoFeB 박막의 저주파수 투자율 측정
윤석수(Seok Soo Yoon),김동영(Dong Young Kim) 한국자기학회 2020 韓國磁氣學會誌 Vol.30 No.1
We measured the permeability of amorphous CoFeB thin film by using second harmonic signals of planner Hall resistance (PHR) sensor. The permeability of amorphous CoFeB thin film measured using PHR sensor was constant value in the low frequency range of 10 Hz~50 kHz. The measured high frequency permeability of amorphous CoFeB thin film was analyzed by complex permeability equation in order to compare with the low frequency permeability. We confirmed that the constant value of low frequency permeability was correspond to the initial permeability of amorphous CoFeB thin film. Thus the PHR sensor could be used to the low frequency permeameter.
탄소강 강판에 대한 저주파수 와전류 신호의 두께 의존성 연구
윤석수(Seok Soo Yoon),김동영(Dong Young Kim) 한국자기학회 2020 韓國磁氣學會誌 Vol.30 No.6
We analyzed the thickness dependence of eddy current (EC) signals measured using a AMR based EC sensor in ferromagnetic SM20C carbon steel plate. The high frequency EC signals showed nearly constant value with thickness. While in the low frequency EC signals, the amplitude was exponentially decreased and the phase was linearly increased, respectively. The phase of EC signals was more sensitive than the amplitude of EC signals with thickness of carbon steel plate. Thus the phase of low frequency EC signals can be applied for the thickness measurement of ferromagnetic carbon steel plate.
전기도금 된 Cu/Ni<SUB>80</SUB>Fe<SUB>20</SUB> 코어/쉘 복합 와이어에서 자기임피던스 및 자기완화
윤석수(Seok Soo Yoon),조성언(Seong Eon Cho),김동영(Dong Young Kim) 한국자기학회 2015 韓國磁氣學會誌 Vol.25 No.1
The model for the magneto-impedance of composite wires composed of highly conductive nonmagnetic metal core and soft magnetic shell was derived based on the Maxwell’s equations. The Cu(100 μm diameter)/Ni<SUB>80</SUB>Fe<SUB>20</SUB>(15 μm thickness) core/shell composite wire was fabricated by electrodeposition. The impedance spectra for the Cu/Ni<SUB>80</SUB>Fe<SUB>20</SUB> core/shell composite wire were measured in the frequency range of 10 kHz~10 MHz under longitudinal dc magnetic field in 0 Oe~200 Oe. The spectra of complex permeability in circumferential direction were extracted from the impedance spectra by using the derived model. The extracted spectra of complex permeability showed relaxation-type dispersion which is well curve-fitted with Debye equation with single relaxation frequency. By analyzing the magnetic field dependence of the complex permeability spectra, it has been verified that the composite wire has magnetic anisotropy in longitudinal direction and the origin of the single relaxation process is the magnetization rotation in circumferential direction.