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이방성 자기저항측정을 이용한 NiO / NiFe 박막의 교환결합연구
김종기(Jong-Kee Kim),김선욱(Sun-Wook Kim),이기암(Ky-Am Lee),이상석(Sang-Suk Lee),황도근(Do-Guwn Hwang) 한국자기학회 2002 韓國磁氣學會誌 Vol.12 No.4
We report an experimental evidence of coexistence of the strong and weak exchange couplings in unidirectional NiO/NiFe (antiferromagnetic/ferromagnetic) bilayer thin films. The exchange bias was measured by VSM and AMR techniques and then, analyzed into the strong and weak exchange couplings by means of a regression method. In NiO(60 ㎚)/NiFe(10 ㎚) film, the ratio of the weak exchange coupling field over the average exchange coupling field was found to be almost unchanged within a range from 0.2 to 0.4 irrespective to the strength of an applied field. However, the ratio increased among the samples with decreasing the average exchange coupling field due to the increment of the weak exchange coupling area.
자연산화된 자유층을 갖는 NiO 스핀밸브 박막의 자기저항특성
김종기(Jong-Kee Kim),주호완(Ho-Wan Joo),이기암(Ky-Am Lee),황도근(Do-Guwn Hwang),이상석(Sang-Suk Lee),박달호(Dal-Ho Park) 한국자기학회 2001 韓國磁氣學會誌 Vol.11 No.3
The effect of specular electron scattering on natural oxidation of free layer in NiO spin valves have been investigated. The magnetoresistance (MR) ratio and the exchange biasing field (Hex) of NiO(600 Å)/Ni_(81)Fe_(19)(50 Å)/Co(7 Å)/Cu(20 Å)/ Co(7 Å)/Ni_(81)Fe_(19)(70 Å) spin valves were increased from 4.9 % to 7.3 %, and 110 Oe to 170 Oe after natural oxidation in the atmosphere for 80 days, respectively. The sheet resistivity p decreased from 28 μΩm to 17 μΩm, but Δp did not almost change after the oxidation. The spin valves enhanced by the specular electron scattering in the naturally oxidized Co/NiFe/NiFeOx, free layer were confirmed from the depth profiles using Auger electron spectroscopy.
SHR에 alpha-Methyldopa를 Timolol 또는 Labetalol과 병용투여시 혈압강하효과에 관한 연구
김종기(Jong Kee Kim),허인회(In Hoi Huh),김재완(Jae Wan Kim) 대한약학회 1981 약학회지 Vol.25 No.2
The antihypertensive effect of alpha-methyldopa administered concurrently with timolol or labetalol were studied with spontaneously hypertensive rats (SHR). Every drugs were administered orally once a day after prechecking the systolic blood pressure and heart rate of SHR. The blood pressure and heart rate of SHR were significantly decreased in groups of combination while those of non-combination groups were fallen slightly. Compared with control group, the significant changes of blood pressure was observed in group of alpha-methyldopa with timolol (100mg + 2mg/kg)and alpha-methyldopa with labetalol (100mg + 12.5mg/kg). The group of alpha-methyldopa with timolo 1 (100mg + 1.Omg/kg) reduced blood Pressure in similar degree as manifested in group of alpha-methyldopa with labetalol (100mg + 50mg/kg.). In the group that alpha-methyldopa was administered concurrently with timolol, the maximum antihypertensive effect and heart rate decreasing effect were appeared after 3 hr and 1 hr of administration respectively and those effects in group of alpha-methyldopa with labotalol were appeared after 6 hr of administration. The acute oral toxicity test was performed using albino mice with alpha-methyldopa alone, alpha-methyldopa with timolol (100:1) and alpha-methyldopa with labetalol (4:1), and was found that the LD50 of alpha-methyldopa alone was 1104mg/kg, alpha-methyldopa with timolol (100:1) was 1115mg/kg and alpha-methyldopa with labetalol (4:1) was 354mg/kg.
α-Fe₂O₃ / NiFe / Cu / NiFe 스핀밸브 박막에서의 자기저항 특성에 대한 연구
김종기(Jong-Kee Kim),주호완(Ho-Wan Joo),이기암(Ky-Am Lee),황도근(Do-Guwn Hwang),이상석(Sang-Suk Lee) 한국자기학회 2000 韓國磁氣學會誌 Vol.10 No.1
We investigated the magnetoresistance effect and the exchange coupling of antiferromagnetic Fe₂O₃ spin-valve film. The X-ray diffractions of the spin-valve films having a different thickness of a α-Fe₂O₃ were measured. The exchange coupling field (Hex) between Fe₂O₃ and pinned NiFe layer was increased from 13.5 Oe to 84.5 Oe, as the thickness of Fe₂O₃ increased from 400 Å to 800 Å. The surface roughness of α-Fe₂O₃ spin-valves increased with the increase of α-Fe₂O₃ thickness. Therefore, the increase of Hex will be due to the increase of the interface roughness. The MR ratios as a function of Fe₂O₃ thickness was not changed. And Hex increased by the increment of magnetostatic coupling between Fe₂O₃ and NiFe (pinned-layer) due to the increment of interface roughness. Hex depends on the surface roughness, but the magnetoresistance ratio doesn't.