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Temperature Dependence of Exchange Coupling on Magnetic Tunnel Junctions
Yongkang Hu,CheolGi Kim,Tomasz Stobiecki,Chong-Oh Kim,Kimin Hong 한국자기학회 2003 Journal of Magnetics Vol.8 No.1
Magnetic Tunnel Junctions (MTJs) were fabricated on thermally oxidized Si (100) wafers using DC magnetron sputtering. The film structures were Ta(50 Å)/Cu(100 Å)/Ta(50 Å)/Ni_(80)Fe_(20)(20 Å)/Cu(50 Å)/Mn_(75)Ir_(25)(100 Å)/Co_(70)Fe_(30)(25 Å)/Al-O(15 Å)/Co_(70)Fe_(30)(25 Å)/Ni_(80)Fe_(20)(t)/Ta(50 Å), with t = 0 Å, 100 and 1000 Å, respectively. X-ray diffraction has shown improvement of (111) texture of IrMn₃ and Cu by annealing. The exchange-biased energy is almost inversely proportional to temperature. The difference between the coercivity Hc and the exchange biased field H_E for t = 0 Å sample is smaller than that for t = 1000 Å. For the pinned layer, the decreasing rate of the coercivity with the temperature is higher compared to that of the exchange field, but variation of Hc is similar to that of the exchange field for free layer.
Centrifugal Infiltration Process of Fibrous Tubular Preform by Al-Cu Alloy
Li, Yanhong,Wang, Kai,Su, Yongkang,Hu, Guoxin The Korean Society for Composite Materials 2009 Advanced composite materials Vol.18 No.4
The kinetics of centrifugal infiltration of fibrous tubular preform is built theoretically, and simulations are conducted to study the effects of various casting conditions on infiltration kinetics and macrosegregation by combining with the energy, mass and kinetic equations. A similarity way is used to simplify the one-dimensional model and the parameter is ascertained by an iterative method. The results indicate that the increase of superheat, initial preform temperature, porosity tends to enlarge the remelting region and decrease copper solute concentration at the infiltration front. Higher angular velocity leads to smaller remelting region and solute concentration at the tip. The pressure in the infiltrated region increase significantly when the angular velocity is much higher, which requires a stronger preform. It is observed that the pressure distribution is mainly determined by the angular velocity, and the macrosegregation in the centrifugal casting is greatly dependent on the superheat of inlet metal matrix, initial temperature and porosity of the preform, and the angular velocity.
2차원 자화벡터를 이용한 퍼멀로이 박막의 이방성자기저항 해석
이영우(Young-woo Lee),호영강(Yongkang Hu),임재준(Jae-joon Lim),김철기(CheolGi Kim),김종오(Chong Oh Kim),윤대식(Tae Sick Yoon) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.4
We measured in-plane 2 dimensional magnetization vector using two pick-up coil sets and investigate the relationship between magnetization vector and anisotropic magnetoresistance. We can determine magnetization vector by measuring magnetic moment in x and y direction simultaneously. As the uniaxial magnetic anisotropy of permalloy film increases, magnetoresistance approaches the expectation which is calculated from the angle between current vector and magnetization vector. Magnetoresistance ratio is linearly proportional to the y moment magnitude which is parallel to the current direction.