本文選題：磁性薄膜 + 溫度梯度�。� 參考：《北京科技大學(xué)》2017年博士論文

【摘要】：磁性功能薄膜材料在當(dāng)今的信息存儲、邏輯和傳感領(lǐng)域擁有廣闊的應(yīng)用前景。然而,目前對于磁性薄膜的研究主要針對其在電輸入信號下的性能和應(yīng)用:一方面,利用其自旋相關(guān)輸運特性的功能器件在工作時,幾乎都以電信號作為輸入源;另一方面,對其磁性能的控制手段也主要基于電控的方式,如利用鐵電基底或自旋轉(zhuǎn)移矩來實現(xiàn)薄膜的磁化翻轉(zhuǎn)等等。這些局限于電控的使用方法和控制方法,不但限制了磁性薄膜材料的應(yīng)用功能,還會因焦耳熱的存在而引起散熱和能耗困擾。圍繞以上問題,本論文提出了"溫控"的手段,并從磁性薄膜在"空間溫差下的輸運行為"和在"升(降)溫控制下的磁性變化"這兩個方面,對溫控下的磁性功能薄膜材料做出了系統(tǒng)的研究。主要研究內(nèi)容如下:(1)研究了MgO包覆的NiFe薄膜在溫差下的自旋相關(guān)輸運行為。一方面,在平行于溫差方向上,450℃退火后MgO(3)/Ni81Fe19(10)/MgO(2)/SiO2(1)(單位為nm)薄膜樣品的塞貝克系數(shù)(Sxxavg.)較制備態(tài)提升了343%,這可以歸因為MgO結(jié)晶對電子界面散射作用的增強;與此同時,樣品的各向異性磁溫差電效應(yīng)(AMT)僅較制備態(tài)增大了139%,我們推測這是由于制備態(tài)時被氧化了的界面處Fe元素在退火后得到還原所致。另一方面,在垂直于溫差方向上,樣品的平面能斯特效應(yīng)(PNE)也在退火后得到了增強,450℃退火后其橫向的塞貝克系數(shù)(Sxy)達(dá)到了73.1nV/K。(2)觀測并研究了NiFe薄膜在溫差和電流共同調(diào)節(jié)作用下出現(xiàn)的溫差增強磁電阻(ThMR)現(xiàn)象。對厚度為10nm的NiFe薄膜樣品同時施加0.966μV電流和2.5℃/mm溫度梯度時,其ThMR值可達(dá)-22600%。此外,這一ThMR還可以通過改變所施加的電流和溫度梯度的相對大小來調(diào)節(jié)。例如本研究中,當(dāng)溫度梯度固定為2.5℃/mm、輸入從0.85μA到1.05μA之間的電流時,即可對樣品的ThMR值在-259%到183%的范圍內(nèi)做出調(diào)控;而隨后固定電流大小不變、改變所施加的溫度梯度大小的實驗也對ThMR值做出了相似的調(diào)控。這一現(xiàn)象的物理本質(zhì)在于NiFe薄膜中自旋相關(guān)散射引起的磁電阻效應(yīng)(MR)與磁溫差電效應(yīng)(MT)擁有相反符號。(3)通過在垂直磁各向異性Co/Ni多層膜的Ni/Co界面間插入Au插層,改善了該類材料在熱處理后出現(xiàn)的磁性能下降的情況。經(jīng)過350℃退火后,結(jié)構(gòu)為Ta(3)/Pt(2)/[Co(0.3)/Ni(0.6)/Au(0.3)]×3/Co(0.3)/Pt(1)/Ta(3)(單位為nm)的樣品的有效磁各向異性能(Keff)仍保持在0.48×105 J/m3。通過STEM-HAADF電鏡照片分析,我們認(rèn)為這一結(jié)果的原因在于Au插層阻礙了其兩側(cè)Ni層和Co層在退火過程中的相互擴散。此外,通過與具有Pt插層的Co/Ni多層膜對比,我們發(fā)現(xiàn)Au插層幾乎不會對該材料體系帶來額外的界面垂直磁各向異性(界面PMA)。這讓帶有Au插層的Co/Ni多層膜有可能成為MRAM用垂直磁各向異性材料的競爭者之一。(4)設(shè)計了NiTi形狀記憶合金基底/Fe薄膜復(fù)合材料,并研究了其在溫度控制下的磁各向異性變化。經(jīng)過200℃、1分鐘的升溫控制并回到室溫后,單程NiTi基底/Fe(5nm)薄膜樣品的面內(nèi)磁各向異性有所增大。X射線光電子能譜(XPS)表征和第一性原理計算顯示,單程NiTi基底在升溫控制下發(fā)生的尺寸縮小使Fe薄膜受到了壓應(yīng)變作用的影響,這會降低Fe晶格內(nèi)沿z方向電子產(chǎn)生的自旋軌道耦合(SOI)作用,并最終使Fe薄膜的面內(nèi)磁各向異性增大。類似地,雙程NiTi基底/Fe(5nm)薄膜樣品則會在"升溫、降低溫、升溫"或"降低溫、升溫、降低溫"的循環(huán)溫控下產(chǎn)生可逆的面內(nèi)磁各向異性變化。
[Abstract]:Functional magnetic thin film materials in the information storage, has a broad application prospect and logic of the sensing field. However, current research on magnetic thin films mainly for its performance and application in electric input signal under: on the one hand, the use of the spin dependent transport properties of functional devices at work, almost all the electrical signals as the input source; on the other hand, the control means on the magnetic properties are mainly based on the way, such as the use of ferroelectric substrate or the spin transfer torque to achieve the magnetization reversal film and so on. These limitations using in the electric control method and control method, not only limits the application of functional magnetic thin film materials, but also because of the presence of Joule heat caused by heat and energy consumption problems. Based on the above problems, this paper puts forward "control" means, and from the magnetic thin film in the "space temperature transport behavior" and "on the rise (fall) temperature control system under the These two aspects of magnetic changes ", made a systematic research on the functional magnetic thin film materials under temperature control. The main contents are as follows: (1) spin dependent transport of NiFe films coated with MgO in the temperature of the transport behavior. On the one hand, in parallel to the direction of temperature, annealing after MgO (450 DEG C 3) /Ni81Fe19 (10) /MgO (2) /SiO2 (1) (nm) films of Sebek coefficient (Sxxavg.) was prepared by state raised 343%, this can be attributed to the crystallization of MgO to enhance the electron interface scattering effect; at the same time, the sample magnetic anisotropic thermoelectric effect (AMT) is only the prepared state increased by 139%, we speculate that this is due to the interface element Fe preparation state is oxidized by reduction induced after annealing. On the other hand, in the direction perpendicular to the plane of the sample temperature, Nernst effect (PNE) was enhanced after annealing, annealing at 450 DEG C after the transverse Sebek The coefficient (Sxy) to 73.1nV/K. (2) observation and Research on the NiFe films under the action of the regulation of temperature enhanced magnetic resistance common temperature and current (ThMR). The thickness of NiFe thin films on 10nm and applied 0.966 V current and 2.5 DEG /mm temperature gradient, the ThMR value can reach -22600%. in addition. The relative size of the ThMR but also by changing the applied current and temperature gradient to adjust. For example in this study, when the temperature gradient is fixed at 2.5 DEG /mm, input from 0.85 A to 1.05 A between the current, can be ThMR of sample to make regulation within the range of -259% to 183%; and then the fixed current size unchanged, changing the applied temperature gradient experiments have made similar regulation of ThMR value. The physical nature of this phenomenon lies in the magnetoresistance of NiFe thin films in spin scattering (MR) and magnetic thermoelectric effect (MT) 鎷ユ湁鐩稿弽絎﹀彿.(3)閫氳繃鍦ㄥ瀭鐩寸鍚勫悜寮傛，

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