Browsing by Author "Hsieh, L. C."

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Characterization of a nano-oxide layer in a pseudo spin valve by complex magneto-impedance spectroscopy
(2006-10-01)
Chien, W. C.
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Peng, T. Y.
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Hsieh, L. C.
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Lo, C. K.
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Yao, Y. D.
The ac properties of a pseudo spin valve (PSV) consisting of NOLtop/Co/Cu/Co/Ni80Fe20/NOLbottom with a top and bottom nanooxide layer (NOL) were studied as functions of NOL and thickness, d, by magneto impedance spectroscopy. The NOLs were formed by natural oxidizing the top and bottom ferromagnetic or Ta layers in situ. The increase in the thickness of NOL resulting in the increment of caused the shift of roll-off frequency from low to high. The frequency dependence behavior of this NOLtop/PSV/NOLbottom system can be modeled by equivalent circuit theory. PSV with a different NOL structure can be checked by such a nondestructive analysis method.
Enhancement and inverse behaviors of magnetoimpedance in a magnetotunneling junction by driving frequency
(2006-11-13)
Chien, W. C.
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Lo, C. K.
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Hsieh, L. C.
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Yao, Y. D.
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Han, X. F.
The magnetoimpedance effect was employed to study magnetotunneling junction (MTJ) with the structure of Ru(5 nm)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al(1.2 nm)-oxide/CoFeB(4 nm)/Ru(5 nm). A huge change of more than +/- 17 000% was observed in the imaginary part of the impedance between the magnetically parallel and antiparallel states of the MTJ. The inverse behavior of the magnetoimpedance (MI) loop occurs beyond 21.1 MHz; however, the normal MI at low frequency and the inverse MI at high frequency exhibit the same magnetization reversal as checked by the Kerr effect. The reversal in MI was due to the dominance of magnetocapacitance at high frequency. (c) 2006 American Institute of Physics.
High frequency impedance inverse in MTJ junction
(2007-03-01)
Hsieh, L. C.
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Huang, Y. W.
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Han, X. F.
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Zeng, Z. M.
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Chien, W. C.
The magnetoimpedance effect of magnetic tunnel junction ( MTJ) was investigated at room temperature in the frequency ranged from 100 Hz to 15 MHz. The MR loop with a ratio of 9.49% at 5MHz switches to - 11.51% at 7 MHz, respectively. This indicates the MR loop reverse shape and sign around 6 MHz. This inverse MR effect is explained by the impedance competition among Resistor- Inductor series circuit and Capacitor part. (c) 2006 Elsevier B. V. All rights reserved.
Oscillating voltage dependence of high-frequency impedance in magnetic tunneling junctions
(2007-06-01)
Chien, W. C.
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Hsieh, L. C.
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Peng, T. Y.
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Lo, C. K.
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Yao, Y. D.
Oscillating voltage (V-Os), which depends on the frequency dependence of the magnetoimpedance (MI) effect, was applied to study a magnetic tunneling junction (MTJ) of Ru(5 mn)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al-2 O-3/CoFeB(4 nm)/Ru(5 nm) at frequencies up to 40 MHz. The MI ratio decreased as the V-Os. was increased. The MI ratio turned from positive to negative at a certain frequency. An equivalent circuit model was employed to analyze the results. The fact that MTJ can be regarded as the composition of a resistance component and two sets of parallel resistance (R) and capacitance (C) components in series has been utilized to describe the individual impedance contribution from the lead of cross pattern, barrier, and interface. The resistance (R-barrier) and capacitance (C-barrier) of the barrier effect are functions of V-Os. The R-barrier decreases as the V-Os increases, However, Cbarrier behaves the opposite way. The tendency is for interfacial resistance R-interface and interfacial capacitance C-interface to have opposite results with increasing V-Os. This work provides a detailed investigation of high-frequency transport behavior subjected to V-Os, especially useful for MTJ characterization.