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首頁> 外文學(xué)位 >Effect of Rare-Earth Incorporation in Ferromagnetic Metals for Magnetic Domain Wall Devices.
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Effect of Rare-Earth Incorporation in Ferromagnetic Metals for Magnetic Domain Wall Devices.

機(jī)譯：稀土摻入鐵磁金屬中對磁疇壁器件的影響。

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摘要

Devices that utilize propagation of magnetic domain walls are of interest for memory and logic applications. These devices are inherently non-volatile and have the potential for major reductions in energy consumption and required power dissipation. However, the speed of these devices must increase to compete with conventional electronics and the energy required to switch and propagate magnetic domains must be reduced to achieve low-power operation.;While Permalloy wires have been widely studied in recent years for domain wall based device applications, domain walls propagated by a spin-polarized current through Permalloy require high critical current densities to initiate domain wall motion and exhibit low velocities. Domain wall dynamics caused by an applied current are not yet fully understood and must be further explored and optimized to establish domain wall device concepts as viable technologies. Magnetization dynamics depend strongly on material properties yet utilization of materials engineering to provide insight and enhancements in dynamics is an area that has not been adequately explored.;In this work, we study novel magnetic metal alloys created by doping ferromagnetic materials with rare-earth elements and evaluate their potential to enhance domain wall dynamics thereby improving domain wall device performance. We focus on Gd dopants that reduce magnetization of magnetic transition metals by antiferromagnetic coupling while still maintaining a low Gilbert damping factor. Dopant atoms should also act as scattering centers that reduce the spin-flip length thus enhancing the non-adiabatic spin torque factor. The static magnetic properties and crystallinity of various film compositions incorporating Gd dopants in Permalloy, Ni and Co are characterized by SQUID magnetometry and XRD measurements. The measurements confirm that Gd dopants decrease the film magnetization and destroy the film crystallinity creating amorphous films with low coercive fields.;Measurements analyzing the effect of Gd dopants on magnetization dynamics are limited to doped Permalloy films because Permalloy has the lowest Gilbert damping factor and has been extensively characterized. FMR measurements demonstrate a small effect on the Gilbert damping factor and verify that co-sputtering yields high-quality uniform thin films. The spin transfer velocity and current polarization are measured using a spin wave Doppler technique. Through measurements, it was found for the first time, that introducing Gd dopants results in a considerable reduction in current polarization which reduces the spin transfer velocity.;These results are verified with the first domain wall velocity measurements through PyGd wires performed using time-resolved MOKE magnetometry. The spin transfer velocity for Permalloy reduces by 30% for the Py0.921Gd 0.079 composition. The effect of the non-adiabatic spin torque contribution is determined through current-assisted domain wall depinning measurements. An unexpected negative spin torque effect is measured for two of the PyGd compositions implying a negative non-adiabatic factor.;In summary, this work explores new magnetic materials and provides insight into current-induced domain wall dynamics that can be used to enhance the domain wall velocity for device applications. These findings indicate that rare-earth dopants are useful for devices utilizing magnetic field propagation resulting in similar velocities as Permalloy but at lower magnetic fields. However, for devices that propagate domain walls using spin-polarized current, the rare-earth doping technique is not beneficial due to the unexpected degradation in spin torque efficiency. This work is the first of its kind to reveal this mechanism and provides insight into the impact of rare-earth incorporation on domain wall dynamics. Although these devices may not provide the expected increase in velocity, the use of rare-earth dopants in magnetic materials provides a platform to study domain wall dynamics by allowing the tuning of material parameters and correlating the impact on domain wall velocities.
機(jī)譯：利用磁疇壁的傳播的設(shè)備對于存儲器和邏輯應(yīng)用是令人感興趣的。這些設(shè)備本質(zhì)上是非易失性的，有可能大大降低能耗和所需的功耗。但是，這些設(shè)備的速度必須提高才能與常規(guī)電子設(shè)備競爭，并且必須降低轉(zhuǎn)換和傳播磁疇所需的能量，以實(shí)現(xiàn)低功耗運(yùn)行。雖然近年來坡莫合金線已被廣泛研究用于基于疇壁的設(shè)備在應(yīng)用中，自旋極化電流通過坡莫合金傳播的疇壁需要很高的臨界電流密度，以啟動疇壁運(yùn)動并表現(xiàn)出低速度。由外加電流引起的疇壁動力學(xué)尚未完全理解，必須進(jìn)一步探索和優(yōu)化以將疇壁設(shè)備概念確立為可行的技術(shù)。磁化動力學(xué)在很大程度上取決于材料的性能，但是材料工程的利用來提供動力學(xué)的見解和增強(qiáng)是一個尚未充分探索的領(lǐng)域。在這項工作中，我們研究了用稀土元素?fù)诫s鐵磁材料制成的新型磁性金屬合金并評估其增強(qiáng)疇壁動力學(xué)從而改善疇壁設(shè)備性能的潛力。我們專注于通過反鐵磁耦合降低磁性過渡金屬磁化強(qiáng)度同時仍保持較低的吉爾伯特阻尼系數(shù)的Gd摻雜劑。摻雜原子還應(yīng)充當(dāng)散射中心，以減少自旋翻轉(zhuǎn)長度，從而增強(qiáng)非絕熱自旋扭矩因子。通過SQUID磁力測定法和XRD測量來表征在坡莫合金，Ni和Co中摻有Gd摻雜劑的各種膜組合物的靜磁性能和結(jié)晶度。這些測量結(jié)果證實(shí)了Gd摻雜劑會降低薄膜的磁化強(qiáng)度并破壞薄膜的結(jié)晶度，從而形成具有低矯頑場的非晶薄膜。被廣泛表征。 FMR測量顯示出對吉爾伯特阻尼因子的影響很小，并驗(yàn)證了共濺射可產(chǎn)生高質(zhì)量的均勻薄膜。使用自旋波多普勒技術(shù)測量自旋傳遞速度和電流極化。通過測量，首次發(fā)現(xiàn)引入Gd摻雜劑可顯著降低電流極化，從而降低自旋轉(zhuǎn)移速度;這些結(jié)果已通過使用時間分辨的PyGd線進(jìn)行的第一疇壁速度測量得到了驗(yàn)證MOKE磁力計。對于Py0.921Gd 0.079組合物，坡莫合金的自旋轉(zhuǎn)移速度降低了30％。非絕熱自旋轉(zhuǎn)矩貢獻(xiàn)的影響是通過電流輔助疇壁去釘測量確定的。測量了兩種PyGd成分的意想不到的負(fù)自旋扭矩效應(yīng)，這表明存在負(fù)非絕熱因子?？傊?，這項工作探索了新的磁性材料，并深入了解了電流感應(yīng)的疇壁動力學(xué)，可用于增強(qiáng)疇設(shè)備應(yīng)用的壁速度。這些發(fā)現(xiàn)表明，稀土摻雜劑可用于利用磁場傳播的設(shè)備，該設(shè)備產(chǎn)生與坡莫合金相似的速度，但磁場較低。但是，對于使用自旋極化電流傳播疇壁的設(shè)備，稀土摻雜技術(shù)由于自旋轉(zhuǎn)矩效率的意外降低而無益。這項工作是首次揭示這種機(jī)制，并提供了稀土摻入對疇壁動力學(xué)影響的見解。盡管這些設(shè)備可能無法提供預(yù)期的速度提高，但在磁性材料中使用稀土摻雜劑可以通過調(diào)節(jié)材料參數(shù)并關(guān)聯(lián)對疇壁速度的影響，提供研究疇壁動力學(xué)的平臺。

著錄項

  • 作者

    Thomas, Rebecca Lynn.;

  • 作者單位

    North Carolina State University.;

  • 授予單位 North Carolina State University.;
  • 學(xué)科 Engineering Electronics and Electrical.;Engineering Materials Science.;Physics Solid State.
  • 學(xué)位 Ph.D.
  • 年度 2012
  • 頁碼 138 p.
  • 總頁數(shù) 138
  • 原文格式 PDF
  • 正文語種 eng
  • 中圖分類
  • 關(guān)鍵詞

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