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비정질 CoFeSiB 자유층을 갖는 자기터널접합의 스위칭 특성
황재연(J. Y. Hwang),이장로(J. R. Rhee) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.6
The switching characteristics of magnetic tunnel junctions (MTJs) comprising amorphous ferromagnetic CoFeSiB free layer have been investigated. CoFeSiB was used for the free layer to enhance the switching characteristics. The typical junction structure was Si/ SiO₂/Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO<SUB>x</SUB>/CoFeSiB (t)/Ru 60 (in ㎚). CoFeSiB has low saturation magnetization (M<SUB>s</SUB>) of 560 emu/㎤ and high anisotropy constant (K<SUB>u</SUB>) of 2,800 erg/㎤. These properties caused low coercivity (H<SUB>c</SUB>) and high sensitivity in MTJs, and it also confirmed in submicrometer-sized elements by micromagnetic simulation based on the Landau-Lisfschitz-Gilbert equation. By increasing CoFeSiB free layer thickness, the switching characteristics became worse due to increase of the demagnetization field.
Bottom형 IrMn 스핀밸브 박막의 열적안정성과 높은 교환결합력
황재연(J. Y. Hwang),김미양(M. Y. Kim),이장로(J. R. Rhee) 한국자기학회 2002 韓國磁氣學會誌 Vol.12 No.2
IrMn pinned spin valve (SV) films with stacks of Ta/NiFe/IrMn/CoFe/Cu/CoFe/NiFe/Ta were prepared by dc sputtering onto thermally oxidized Si (111) substrates at room temperature under a magnetic field of about 100 Oe. The annealing cycle number and temperature dependence of exchange coupling field (Hex), magnetoresistance (MR) ratio, and coercivity (Hc) were investigated. By optimizing the process of deposition and post thermal annealing condition, we obtained the IrMn based SV films with MR ratio of 3.6 %, Hex of 1180 Oe for the pinned layer. The Hex is stabilized after the second annealing cycle and it is thought that this SV reveals high thermal stability. The Hex maintained its strength of 600 Oe in operation up to 240 ℃ and decreased monotonically to zero at 270 ℃.
황재연(J. Y. Hwang),이장로(J. R. Rhee) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.6
We studied the specular spin valve (SSV) having the spin filter layer (SFL) in contact with the ultrathin free layer composed of Ta3/NiFe2/IrMn7/CoFe1/(NOL1)/CoFe2/Cu1.8/CoFe(t_F)/Cu(t_(SF))/(NOL2)/Ta3.5 (in ㎚) by the magnetron sputtering system. For this anti ferromagnetic Ir₂₂Mn_(78)-pinned spin filter specular spin valve (SFSSV) films, an optimal magnetoresistance (MR) ratio of 11.9% was obtained when both the free layer thickness (t_F) and the SFL thickness (t_(SF)) were 1.5 ㎚, and the MR ratio higher than 11% was maintained even when the t_F was reduced to 1.0 ㎚. It was due to increase of specular electron by the nano-oxide layer (NOL) and of current shunting through the SFL. Moreover, the interlayer coupling field (H_int) between free layer and pinned layer could be explained by considering the RKKY and magnetostatic coupling. The coercivity of the free layer (Hcf) was significantly reduced as compared to the traditional spin valve (TSV), and was remained as low as 4 Oe when the t_F varied from 1 ㎚ to 4 ㎚. It was found that the SFL made it possible to reduce the free layer thickness and enhance the MR ratio without degrading the soft magnetic property of the free layer.
비정질 CoFeSiB 단일 및 합성형 반강자성 자유층을 갖는 자기터널접합의 자기저항 효과
황재연(J. Y. Hwang),김순섭(S. S. Kim),이장로(J. R. Rhee) 한국자기학회 2005 韓國磁氣學會誌 Vol.15 No.6
To obtain low switching field (Hsw) we introduced amorphous ferromagnetic Co_(70.5)Fe_(4.5)Si_(15)B_(10) single and synthetic antiferromagnet(SAF) free layers in magnetic tunnel junctions (MTJs). The switching characteristics for MTJs with structures Si/SiO₂/Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlOx/CoFeSiB 7 or CoFeSiB (t)/Ru 1.0/CoFeSiB (7-t)/Ru 60 (in ㎚) were investigated and compared to MTJs with Co_(75)Fe_(25) and Ni_(80)Fe_(20) free layers. CoFeSiB showed a lower saturation magnetization of 560 emu/㎤ and a higher anisotropy constant of 2,800 erg/㎤ than CoFe and NiFe, respectively. An exchange coupling energy (Jex) of -0.003 erg/㎠ was observed by inserting a 1.0 ㎚ Ru layer in between CoFeSiB layers. In the CoFeSiB single and SAF free layer MTJs, it was found that the size dependence of the Hsw originated from the lower Jex experimentally and by micromagnetic simulation based on the Landau-Lisfschitz-Gilbert equation. The CoFeSiB SAF structures showed lower Hsw than that of NiFe, CoFe and CoFeSiB single structures. The CoFeSiB SAF structures were proved to be beneficial for the switching characteristics such as reducing the coercivity and increasing the sensitivity in micrometer to submicrometer-sized elements.
강자성 비정질 NiFeSiB 자유층을 갖는 자기터널접합의 스위칭 특성
황재연(J. Y. Hwang),이장로(J. R. Rhee) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.6
Magnetic tunnel junctions (MTJs), which consisted of amorphous ferromagnetic NiFeSiB free layers, were investigated. The NiFeSiB layers were used to substitute for the traditionally used CoFe and/or NiFe layers with the emphasis being given to obtaining an understanding of the effect of the amorphous free layer on the switching characteristics of the MTJs. Ni₁?Fe?₂Si?B₁₄ has a lower saturation magnetization (M<SUB>s</SUB>: 800 emu/㎤) than Co??Fe₁? and a higher anisotropy constant (K<SUB>u</SUB>: 2,700 erg/㎤) than Ni??Fe₂?. The Si/SiO₂/Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO<SUB>x</SUB>/NiFeSiB t/Ru 60 (in nanometers) structure was found to be beneficial for the switching characteristics of the MTJ, leading to a reduction in the coercivity (H<SUB>c</SUB>) and an increase in the sensitivity resulted from its lower saturation magnetization and higher uniaxial anisotropy. Furthermore, by inserting a very thin CoFe layer at the tunnel barrier/NiFeSiB interface, the TMR ratio and switching squareness were improved more with the increase of NiFeSiB layer thickness up to 11㎚.