鐵─鎳─鎵合金材料的鐵磁共振與磁彈性質研究

Abstract

本實驗計畫為，鐵─鎳─鎵合金材料鐵磁共振與磁彈性質的研究。其中，在膜材的研究方面，我們是利用磁控濺鍍在基板上沉積成薄膜，我們分別沉積系列合金Fe81-xNixGa19於矽基板上，和沉積系列合金Fe81-yNiyGa19於玻璃基板上，其中x、y為0到26。我們已經做的量測主要為：(1)磁滯伸縮的量測、(2)易軸、難軸的磁滯曲線、(3)鐵磁共振的實驗。鐵磁共振在9.6GHz的交變磁場下執行，透過Kittle模型我們可以得到自然共振頻率，再透過磁滯曲線的資訊我們可以得到Gilbert阻尼係數。在薄膜的實驗中，我們得到幾個材料的特性：(1)在系列合金中，磁異向場隨鎳的原子百分比增加而降低、(2)自然共振頻率隨鎳的增加而降低、(3) Gilbert阻尼係數亦隨鎳的原子百分比增加而降低、(4)磁致伸縮的峰值出現在鎳原子百分比為22的時候。其中，特性(1)、(2)和(3)皆因為鎳元素取代鐵元素時降低其合金的磁性，因而降低了磁異向能量，磁異向場亦隨之降低，進而牽動自然共振頻率與Gilbert阻尼係數。特性(4)系因鎳的添加而改變了薄膜的晶相，進而提升薄膜的磁致伸縮。至此，我們發現Fe59Ni22Ga19在玻璃上有很優良的磁彈性質並可以在微波中應用。 Yager、Galt和Merritt指出鐵磁共振的半高寬與磁異向場大小有關，其實驗證明磁異向場越大，則鐵磁共振半高寬越寬，而在系列和金中增加鎳原子百分比可有效降低磁異向場，進而得以降低Gilbert阻尼係數。另外，由XRD的數據顯示，系列合金中鎳原子百分比的增加可有效抑制D019 相與 L12 相的生成，證據顯示，甚至在鎳原子百分比達到22百分比時，合金薄膜中僅存在A2相，D019 相與 L12 相其磁伸縮值皆為負值，不利合金薄膜飽和磁伸縮最佳化，從實驗數據中我們也得到鎳原子百分比達到22百分比的系列合金，有最佳化的飽和磁致伸縮值。 另外，此篇論文也針對Fe81-zNizGa19系列合金薄帶做一系列的探討，其中z為0到24。薄帶樣品是由快速冷淬法所製備而成，由XRD數據顯示，材料的晶格常數與鎳成分的添加有對應關係。由磁滯曲線的觀察，當合金薄帶添加鎳以後，磁異向性能量降至零，變成等向性質的磁性材料，卻也分別降低與提高飽和磁化量和矯頑磁力。從磁彈性質的研究中，我們發現楊氏係數隨鎳原子百分比的增加而降低，並由E效應，使觀察到於系列合金中添加元素鎳的所產優勢，這優勢更進而影響磁致伸縮的大小，我們發現在鎳佔原子百分比為7時，擁有最大的磁致伸縮量。於此結果我們認為Fe74Ni7Ga19合金薄帶有很優良的磁彈性質並可製成元件加以應用。 於鐵─鎵合金中添加鎳元素可以有下降低其的磁異向性，在薄帶研究中，甚至發現鎳元素的添入更可使材料變成等向性，而正是對軟磁材料的應用層面相當有利的一個條件。

Fe81-xNixGa19/Si(100) and Fe81-yNiyGa19/glass films, where x or y = 0 - 26, were made by the magnetron sputtering method. We have performed three kinds of experiments on these films: [i] the saturation magnetostriction (λS) measurement; [ii] the easy-axis and hard-axis magnetic hysteresis loop measurements; [iii] the ferromagnetic resonance (FMR) experiment to find the resonance field (HR) with an X-band cavity tuned at fR = 9.6 GHz. The natural resonance frequency, fFMR, of the Kittel mode at zero external field (H = 0) was then obtained and used to calculate the Gilbert damping constant. The main findings of this study are summarized: [i] HK decreases, as x or y increases; [ii] fFMR decreases, as x or y increases; [iii] α decreases from 0.052 to 0.020 and then increases from 0.020 to 0.050, as x increases, and α decreases from 0.060 to 0.013, as y increases; [iv] λS reaches maximum when x = 22. The reason of the [i], [ii] and [iii] are described below: as addition Ni replaces Fe at.% in alloys magnetism in rich-Fe alloys is reduced. As a result, the magnetic anisotropy energy causes the HK to decrease, and, therefore, fFMR and α also decrease. The reason of [iv]: as addition Ni into Fe81Ga19 alloy films enhances the A2 phase, which is good for λS in the alloys. Thus, we conclude that the Fe59Ni22Ga19/glass film should be suitable for the magneto-electric microwave device applications. Yager, Galt, and Merritt pointed out that ΔH is related to HK. Besides, we find the addition of Ni into Fe81Ga19 alloy films destabilize the D019 phase and L12 phase. Briefly speaking, when y = 22 at.%Ni, there is only one single A2 phase. That centralized the HR and narrow ΔH in the alloys. In Eq. (2), α of the FeNiGa alloy is calculated from ΔH; α decreases, as ΔH decreases. On the other hand, the Fe81Ga19 film with the D019 phase and L12 phase are detrimental to saturation magnetostriction, so we get magnetostriction constants in the FeNiGa ternary alloys higher than those of the Fe81Ga19 binary alloys. Another series of Fe81-zNizGa19 ribbons, where z = 0 - 24, were made by the rapidly quenching method. The X-ray diffraction patterns showed that these ribbons change the lattices constants which depend on number of z. From hysteresis loops information, the ribbons become isotropic in magnetic anisotropy, Ms decreases from 170 emu/g to 116 emu/g, and Hc inceases from 4.8 Oe to 11.7 Oe, as Ni is added in. Young’s modulus (Es) at magnetization saturation and ΔE effect were estimated from the strain curve. We discovered that as z increases,ΔE/E0 increases. The most important result is that λ reaches maximum when z = 7 at.%Ni. We conclude that the Fe74Ni7Ga19 ribbon should be most suitable for the magneto-electric device application. The addition of Ni into Fe81Ga19 alloys refined the magnetic anisotropy energy which let the HK decreases, as Ni content increases. Even in the series Fe81-zNizGa19 ribbons, there becomes isotropic magnetic anisotropy energy.