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이온주입식 자기 버블 전파 회로에서의 자기 버블의 등방성 전파
최연봉,조순철,Choi, Yeon-Bong,Jo, Soon-Chul 대한전자공학회 1990 전자공학회논문지 Vol. No.
자기 응력 계수의 변화에 따른 자기 버블의 등방성 전파 여부를 규명하기 위하여 자기 응력 계수가 거의 등방화(${\lambda}111{\simeq}{\lambda}100$) 된 세가지 버블 가네박막(AK92, AKa8, AKb1)의 바이어스 마진과 버블 소멸 자장을 $2.5{\mu}m$ 주기를 갖는 다이아몬드 패턴에서 측정하였다. 측정 결과 바이어스 마진은 각 박막의 경우 우수, 보통, 열등 회로에서 상당히 등방화된 값을 얻을 수 있었다. 버블 소멸 자장으로부터 회전 자장의 방향에 따른 버블 포텐셜 우물을 구하였다. 버블 포텐셜 우물로부터 자기 응력 이방성 정도를 나타내는 ${\Delta}(=({\lambda}111-{\lambda}100)/{\lambda}111)$값이 0.5인 AK92인 경우 우수, 보통, 열등 회로에서 버블 포텐셜 우물이 상당한 차이가 있는 반면 0.3인 AKa8과 0.1인 AKb1의 경우 각 회로에서 거의 등방화가 이루어진 것을 볼 수 있었다. 위의 두가지 측정 결과에서 ${\Delta}$값이 0.1~0.3일때 거의 등방적인 버블 전파가 일어남을 알 수 있었다. To find out whether isotropic magnetic bubble propagation can be achived by changing magnetostriction coefficients, bias margins and bubble collapse fields of $2.5{\mu}m$ period "diamond" bubble propagation tracks were measured which were fabricated on three magnetic garnet thin films with nearly isotropic magnetostriction coefficients (${\lambda}111{\simeq}{\lambda}100$). The results showed substantially isotropic bubble propagation in "super","good" and "bad" tracks for all three garnet films. From the bubble collapse fields, the bubble potential well depths vs. the direction of the in-plane rotating magnetic fields were plotted. The results showed that substantial differances in the potential well shapes exist for the three "good," "bad" and "super" tracks when ${\Delta}(=({\lambda}111-{\lambda}100)/{\lambda}100)$ was 0.5 (film AK92). However, the differences were minimal when ${\Delta}$ were 0.3 (film Aka8) or 0.1 (film AKb1). In other words, the bubble potential wells were nearly isotropic. The above two measurements indicate that nearly isotropic bubble propagation can be achieved when B is between 0.1 and 0.3.
스핀 밸브 Ta 하지층의 질소함유량 변화와 열처리 온도에 따른 자기적 특성
최연봉(Yeonbong Choi),김지원(Jiwon Kim),조순철(Soonchul Jo),이창우(Chang-Woo Lee) 한국자기학회 2005 韓國磁氣學會誌 Vol.15 No.4
In this research, magnetic properties and annealing effects of the spin valve structures were investigated, which have Ta underlayer deposited with Ar and N₂ gas mixture. Also, TaN underlayer as a diffusion barrier and the substrate were investigated. The structure of the spin valve was Si(SiO₂)/Ta(TaN)/NiFe/CoFe/Cu/CoFe/FeMn/Ta. Deposition rate was decreased and resistivity and roughness of the TaN films were increased as the N₂ gas flow was increased. The XRD results after high temperature annealing showed that Silicides were created in Si/Ta layer, but not in Si/TaN layer. Magnetoresistance ratio (MR) and exchange coupling field (Hex) were decreased when the N₂ gas flow was increased over 4.0 sccm. The MR of the spin valves with Ta and TaN films deposited with up to 4.0 sccm of N₂ gas flow was increased about 0.5 % until the annealing temperature of up to 200℃ and then, decreased. TaN film deposited with 8.0 sccm of N₂ gas flow showed twice the adhesion of the Ta film. The above results indicate that with 3.0 sccm of N₂ gas flow during the Ta underlayer deposition, the magnetic properties of the spin valves are maintained, while the underlayer may be used as a diffusion barrier and the adhesion between the Si substrate and the underlayer is increased.
NiFe / FeMn / NiFe / CoFe / Al₂O₃ / CoFe / NiFe 스핀 터널링 접합의 자기적 특성과 열처리 효과
최연봉(Yeonbong Choi),박승영(Seungyung Park),강재구(Jaegoo Kang),조순철(Soonchul Jo) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.6
DC 마그네트론 스퍼터링 방법으로 금속 마스크를 사용하여 십자형태로 substrate/Ta/NiFe/FeMn/NiFe/CoFe/Al₂O₃/CoFe/NiFe와 substrate/Ta/NiFe/CoFe/Al₂O₃/CoFe/NiFe/FeMn/NiFe 스핀 터널링 접합 구조를 제조하였다. 이러한 구조에서 절연층(Al₂O₃)의 형성조건과 각 층의 두께와 파워에 대한 증착율에 변화를 주어 24.3 %의 자기 저항비를 얻었다. 두 종류의 구조에 대한 자기적 특성 비교와 Coming glass 7059와 Si(111) 기판의 종류에 따른 결과를 비교하였으며 소자 제조 때 수반되는 온도변화에 대한 특성변화를 알아보고자 열처리를 하였다. 열처리 결과 자기 저항비는 150 ℃까지는 어느 정도 일정한 값을 유지하다가 180 ℃ 열처리 후 갑자기 감소하는 결과를 얻었다. Cross-shape structures of spin tunneling junctions were fabricated using DC magnetron sputtering and metal masks. The film structures were substrate/Ta/NiFe/FeMn/NiFe/CoFe/Al₂O₃/CoFe/NiFe and substrate/Ta/NiFe/CoFe/Al₂O₃/CoFe/NiFe/FeMn/NiFe. Fabrication conditions of insulating layer (Al₂O₃) and thickness and sputtering power of each film layer were varied, and maximum magnetoresistance ratio of 24.3 % was obtained. Magnetic characteristic variations in the above mentioned two structures and two types of substrates (Coming glass 7059 and Si(111)) were compared. Annealing of the junctions was performed to find out magnetic characteristic variations expected from the device fabrication. Magneoresistance Ratio were observed to maintain as-deposited value up to 150 ℃ annealing and then to drop rapidly after 180 ℃ annealing.
NiFe / FeMn / NiFe / CoFe / Al₂O₃ / CoFe / NiFe 스핀 터널링 접합의 자기적 특성과 열처리 효과
최연봉(Yeonbong Choi),박승영(Seungyung Park),강재구(Jaegoo Kang),조순철(Soonchul Jo) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.6
DC 마그네트론 스퍼터링 방법으로 금속 마스크를 사용하여 십자형태로 substrate/Ta/NiFe/FeMn/NiFe/CoFe/Al₂O₃/CoFe/NiFe와 substrate/Ta/NiFe/CoFe/Al₂O₃/CoFe/NiFe/FeMn/NiFe 스핀 터널링 접합 구조를 제조하였다. 이러한 구조에서 절연층(Al₂O₃)의 형성조건과 각 층의 두께와 파워에 대한 증착율에 변화를 주어 24.3 %의 자기 저항비를 얻었다. 두 종류의 구조에 대한 자기적 특성 비교와 Coming glass 7059와 Si(111) 기판의 종류에 따른 결과를 비교하였으며 소자 제조 때 수반되는 온도변화에 대한 특성변화를 알아보고자 열처리를 하였다. 열처리 결과 자기 저항비는 150 ℃까지는 어느 정도 일정한 값을 유지하다가 180 ℃ 열처리 후 갑자기 감소하는 결과를 얻었다. Cross-shape structures of spin tunneling junctions were fabricated using DC magnetron sputtering and metal masks. The film structures were substrate/Ta/NiFe/FeMn/NiFe/CoFe/Al₂O₃/CoFe/NiFe and substrate/Ta/NiFe/CoFe/Al₂O₃/CoFe/NiFe/FeMn/NiFe. Fabrication conditions of insulating layer (Al₂O₃) and thickness and sputtering power of each film layer were varied, and maximum magnetoresistance ratio of 24.3 % was obtained. Magnetic characteristic variations in the above mentioned two structures and two types of substrates (Coming glass 7059 and Si(111)) were compared. Annealing of the junctions was performed to find out magnetic characteristic variations expected from the device fabrication. Magneoresistance Ratio were observed to maintain as-deposited value up to 150 ℃ annealing and then to drop rapidly after 180 ℃ annealing.
Ta / NiFe / Co / Cu / Co / NiFe / FeMn 스핀밸브구조에서 Ar 압력과 Co 사이층 두께에 따른 GMR 특성 변화
최연봉(Yeonbong Choi),류상현(Sanghyun Ryu),조순철(Soonchul Jo) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.2
We have studied changes of coercivity (Hc), exchange anisotropy field (Hex) and MR ratio in glass/Ta/NiFeⅠ/CoⅠ(t)/Cu/CoⅡ(3/4 t)/NiFeⅡ/FeMn spin valve structures by changing Ar pressure and thicknesses of Co layers using DC, RF sputtering methods. We obtained minimum coercivity of 2.8 Oe at 4 mTorr of Ar pressure, exchange anisotropy field of 50.0 Oe at 6 mTorr and 5.3 % of MR ratio at 10 mTorr. Also, we obtained 3.0 Oe of coercivity at 40 Å of CoⅠ layer, 65.9 Oe at 13 Å and 4.7 % of MR ratio at 27 Å and 34 Å by changing the thicknesses of Co layers.
RF Diode 스퍼터 방법으로 증착된 FeN 다층 박막의 자기적 특성
최연봉(Y. B. Choi),박세익(S. I. Park),조순철(S. C. Jo) 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.1
FeN thin films for inductive recording heads were sputter deposited using RF diode sputtering method from a pure iron target onto 7059 glass substrates, and their magnetic properties were measured. The magnetic properties were greatly affected by film thickness, gas pressure, sputter power and flow ratio of N₂ to Ar. Single layer FeN films with their thickness varied from 1,000 Å to 6,000 Å were doposited. 800 W sputter power, 3 mT gas pressure, N₂ to AT flow ratio of 6.6 : 100 were the sputtering conditions. Up to 7 layers of FeN films having total thickness of 6,000 Å were deposited using SiO₂ of 30 Å thickness as intermediate layers and their coercivity and saturation magnetization were measured. The sputtering conditions were the same as those in the single layer films. Easy axis coercivity of the single layer FeN films gradually decreased as their thickness was increased, but for the films with their thicknesses above 3,000 Å, the coercivity changed very little. As the number of the FeN layers were increased, the coercivity decreased We estimated the grain size of FeN films from the FWHM (Full Width at Half Maximum) of X-ray diffraction peaks. The grain size steadily decreased from about 200 Å to 120 Å as the number of layers were increased. Minimum hard axis coercivity of 0.4 Oe was obtained when the number of layers was four. Maximum relative permeability was 2,900 when the number of layers was three. The cut off frequency of the multilayer films were above 100 ㎒.