Browsing by Author "Liu, Chi-Ching"

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Ferromagnetic resonance properties of Fe81-xNixGa19/Si(1 0 0) and Fe81-yNiyGa19/glass films
(2013-06-15)
Liu, Chi-Ching
;
Jen, Shien-Uang
;
Juang, Jenh-Yih
;
Lo, Chi-Kuen
;
電子物理學系
Two series of Fe81 xNixGa19/Si(100) and Fe81 yNiyGa19/glass films, where x or y = 0-26, were made by the magnetron sputtering method. The film thickness (t(f)) was fixed at 100 nm. We have performed three kinds of experiments on these films: (i) the saturation magnetostriction (lambda(S)) measurement; (ii) the easy-axis and hard-axis magnetic hysteresis loop measurements; and (iii) the ferromagnetic resonance (FMR) experiment to find the resonance field (H-R) with an X-band cavity tuned at f(R) = 9.6 GHz. The natural resonance frequency, f(FMR), of the Kittel mode at zero external field (H = 0) is defined as f(FMR) (sic) nu[H(K)4-pi M-S](1/2), where gamma = 2 pi nu is the gyromagnetic ratio, H-K and 4 pi M-S are the uniaxial anisotropy field and saturation magnetization, and H-K << 4 pi M-S. The Gilbert damping constant, alpha, is calculated from the formula, alpha = [nu(Delta H)(S)]/(2f(R)), where (Delta H)(exp) = (Delta H)(S) + (Delta H)(A), (Delta H)(exp) is the half-width of the absorption peak around the resonance field H-R, (Delta H)(S) is the symmetric part of (Delta H)(exp), and (Delta H)(A) is the asymmetric part. The degree of asymmetry, (Delta H)(A)/(Delta H)(exp), is associated with the structural and/or magnetic inhomogeneities in the film. The main findings of this study are as follows: (A) f(FMR) tends to decrease, as x or y increases; (B) alpha decreases from 0.052 to 0.020 and then increases from 0.020 to 0.050, as x increases, and a decreases from 0.060 to 0.013 in general, as y increases; and (C) lambda(S) reaches a local maximum when x = 22. We conclude that the Fe59Ni22Ga19/glass film should be the most suitable for application in magneto-electric microwave devices. (C) 2013 Elsevier B.V. All rights reserved.
Magnetic domain studies of La0.7Sr0.3MnO3 film deposited on SrLaAlO3 (001) substrate
(2013-06-26)
Liu, Chi-Ching
;
Chu, Pei-Yuan
;
Chiang, Yao-Wei
;
Juang, Jenh-Yih
;
Jen, Shien-Uang
Epitaxial 120 nm La0.7Sr0.3MnO3 (LSMO) compressively strained thin films were deposited on single-crystalline SrLaAlO3(0 0 1) (SLAO) substrates by the pulsed laser deposition (PLD) method. From the x-ray diffraction study, we confirmed that the c-axis of the LSMO crystal pointed out of the film plane. Two kinds of magnetic experiments were performed on the film: (i) the in-plane (field H (sic) H-P) and the out-of-plane (field H (sic) H-N) magnetic hysteresis loop measurements and (ii) magnetic force microscopy scans. We have proved from both theory and experiment that the LSMO film should exhibit the weak and tilted perpendicular magnetic anisotropy at room temperature (RT), that is, the easy axis (EA) is tilted relative to the film normal by an angle theta(o) is approxiamtely equals to 37 degrees, when the film is in the demagnetized state. The magnetic domain (MD) structure of the demagnetized LSMO film showed a maze-like pattern. Although from the in-plane hysteresis loop, H-P = 600 Oe seems large enough to saturate the film, the corresponding MD structure was not in a single-domain state. Instead, there were two types of MDs: the canted MD and the saturated MD. The MD patterns of the LSMO film between the demagnetized and the remanent states were different. In addition, there were double-switch phenomena in the out-of-plane hysteresis loop. When vertical bar H-N vertical bar congruent to 140 Oe, a transition of the MD pattern from the maze-like to the closure (or dense-stripe) type occurred.