Study on the Structure and Magnetostriction Properties of Fe81-yCoyGa19 thin films
Date Issued
2012
Date
2012
Author(s)
Tsung Lin, Tsai
Abstract
In this research, Fe81-yCoyGa19 films were made by the dc magnetron sputtering method by depositing Fe81-yCoyGa19 thin films on Corning 0211 glass substrate. Herein we investigate the Co-substitution effect on the Fe81Ga19 alloy based on the following: (i) the Co-substitution range is wider, i.e., up to 19 at. %Co; (ii) the structural change from adding Co in the (110) textured Fe81-yCoyGa19 films; (iii) the high frequency performance limited by the eddy current effect electrical resistivity ρ of the FeCoGa films, ρ is about 200μΩ-cm; ( iv) λsincreases steadily from 23 to 56 ppm, as x increases from 0 to 19 at. % Co.
Next, Fe81–yCoyGa19 films, with y=0-23 atom % Co, were deposited on Si(100) substrates, respectively, by the dc magnetron sputtering method. For each alloy target, we prepared six different thickness samples. Film thickness (tf) ranged from 30 to 400 nm. First, Our main finding is that as y increases from 0 to 19 atom % Co, λS increases from 36 to 98 ppm; as y increase for this, from 19 to 23 atom % Co, λS decreases. These results indicate that the addition of Co in the Fe81Ga19 alloy is advantageous in enhancing λS up to y~19% ; second, we that compare the λS of Fe81–yCoyGa19/glass with that of Fe81–yCoyGa19/Si(100); Third, from XRD, the Fe62Co19Ga19/Si(100) film reveals the A2 and B2 phases; Fourth, we analysis of the film thickness (tf) dependencies of λS and coercivity (Hc) of the Fe62Co19Ga19 film was by made; Fifth, the top and bottom interfaces, we performed Auger-depth (AES-DP) profile analysis on one Fe62Co19Ga19/Si(100) film. Sixth, Other physical properties of the Fe62Co19Ga19 films include the following:saturation magnetization 4πMS=1.8–2.0 T, coercivity HC=35–64 Oe, planar (mean) grain size DP=29.6 nm, and columnar grain size DL≈tf. After measuring and analyzing, we can know that the substitution of Co for Fe could give rise to increases in λS, and samples with composition y=19 have the largest magnetostriction.
Furthermore, we measured the magnetic properties of Fe81-xCoxGa19 films at higher temperature. By the measurement of VSM at different temperature, Magnetic hysteresis loops of each film were measured from room temperature (RT) to 8000C. In terms of high temperature magnetic properties,(A) we find that for each film, there is one low-temperature-phase Curie point (TC1) and one high-temperature-phase Curie point (TC2); (B) based on the temperature dependence of 4πMS; (C) we calculated the reduced hyperbolic Bessel function Î5/2 (T); from the relationship λs (T) = λs (RT) × Î5/2 (T), we can compare the performances of λs (T) at higher temperatures; (D) Initially HC decreases slightly as T increases, but it turns around reaches a maximum value when either TC1 or TC2 is approached. It is concluded that the Fe62Co19Ga19 film has the optimal high-temperature magnetic properties, including a larger λs (T), higher TC1, and moderate HC (T).
A good magnetostrictive thin film actuator, transducer, or sensor should acquire following characteristics,large saturation magnetostriction (λS) and low saturation (or anisotropy) field (HS), so that its magnetostriction susceptibility (SH ≡ Δλ/HS ≡ [λ//S - λ⊥S]/HS, where λ//S and λ⊥S are the longitudinal and transverse magnetostriction at HS) can be as large as possible. In this study, we have made Fe62Co19Ga19/Si(100) nano-crystalline films by using the dc magnetron sputtering technique under various fabrication conditions: Ar working gas pressure (pAr) varied from 1 to 15 mTorr, sputtering power (Pw) from 10 to 120 watt, deposition temperature (TS) from room temperature (RT) to 3000C, and film thickness (tf) fixed at 175 nm. The following experiments were performed on films: [1] the atomic force and magnetic force microscope (AFM and MFM), [2] the magnetic hysteresis-loop, [3] the longitudinal and transverse magnetostriction, [4] ferromagnetic resonance (FMR), and [5] the electrical resistivity (ρ) measurements. Each magnetic domain looks like a long leaf, with its long-axis being about 12 to 15 μm and short-axis about 1.5 μm. The optimal magnetic and electrical properties are collected from the Fe62Co19Ga19 film made with the following sputter deposition parameters, such as pAr= 5 mTorr, Pw= 80 watt, and TS = RT. Those optimal properties include λS = 80 ppm, HS = 19.8 Oe, SH = 6.1 ppm/Oe, and ρ = 57.0 μΩ-cm. Note that SH for the conventional magnetostrictive Terfenol-D film is, in general, equal to 1.5 ppm/Oe.
Five series of Fe62Co19Ga19 films were deposited on Si(100) substrates at roomtemperature: they were (IR) Ta/Fe
62Co19Ga19(tf)/Ta/Si(100), (IIR) Ta/Fe62Co19Ga19(tf) /Si(100), (IIIR) Fe62Co19Ga19(tf)/Ta/Si(100), (IVR) Fe62Co19Ga19(tf)/Si(100), and (INR) Ta/Fe62Co19Ga19(tf)/Ta/Si(100), where R means the Si substrate was rotated at a speed of 12 rpm, while depositing Fe62Co19Ga19; NR means the Si substrate not rotated; the thickness of the Ta capping and/or barrier layer was 10 nm; and tf, ranging from 5 to 290 nm, is the thickness of Fe62Co19Ga19 film. We have measured the longitudinal and transverse magnetostriction (λ//S and λ⊥S) at the saturation field Hs for these films. The saturation magnetostriction is defined as λs≡ (2/3)Δλ= (2/3)(λ//s-λ⊥s), and the magnetostriction susceptibility (or sensitivity) as SH≡ (Δλ)/Hs. The main objective of this work is to study the Ta capping and/or barrier layer effect on λs or SH of Fe62Co19Ga19 films. The tf dependence of λs is similar to that of SH for each series of Fe62Co19Ga19 film: as tf decreases from 290nm, λs or SH first increases, reaches the maximum value λsm or SHm at tf= tf(K)m or tf= tf(K)M, where K≡IR to IVR and INR, and finally decreases if tf < tf(K)m or tf < tf (K)M. We found that if there is either a Ta capping or barrier layer, and if there are both, the tf(K)m or tf(K)M value is much reduced, but the λsm or SHm value is ,however, enhanced. The optimal value for λs is about 123 ppm obtained from the (IR)m film and that for SH is 6.1 ppm/Oe from the (IVR)M film, respectively.
Subjects
Magnetostriction
FeCoGa film
Type
thesis
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